In high-resolution X-ray observations of the hot plasma in clusters of galaxies significant structures caused by AGN feedback, mergers, and turbulence can be detected. Many clusters have been observed by Chandra in great depth and at high resolution. Using archival data taken with the Chandra ACIS instrument the aim was to study thermodynamic perturbations of the X-ray emitting plasma and to apply this to better understand the thermodynamic and dynamic state of the intra cluster medium (ICM). We analysed deep observations for a sample of 33 clusters with more than 100 ks of Chandra exposure each at distances between redshift 0.025 and 0.45. The combined exposure of the sample is 8 Ms. Fitting emission models to different regions of the extended X-ray emission we searched for perturbations in density, temperature, pressure, and entropy of the hot plasma. For individual clusters we mapped the thermodynamic properties of the ICM and measured their spread in circular concentric annuli. Comparing the spread of different gas quantities to high-resolution 3D hydrodynamic simulations, we constrain the average Mach number regime of the sample to Mach1D ~ 0.16 +- 0.07. In addition we found a tight correlation between metallicity, temperature and redshift with an average metallicity of Z ~ 0.3 +- 0.1 Z(solar). This study provides detailed perturbation measurements for a large sample of clusters which can be used to study turbulence and make predictions for future X-ray observatories like eROSITA, Astro-H, and Athena.
We explore the relationship between the spectral shape of the Ly{\alpha} emission and the UV morphology of the host galaxy using a sample of 304 Ly{\alpha}-emitting BV i-dropouts at 3 < z < 7 in the GOODS and COSMOS fields. Using our extensive reservoir of high-quality Keck DEIMOS spectra combined with HST WFC3 data, we measure the Ly{\alpha} line asymmetries for individual galaxies and compare them to axial ratios measured from observed J- and H-band (restframe UV) images. We find that the Ly{\alpha} skewness exhibits a large scatter at small elongation (a/b < 2), and this scatter decreases as axial ratio increases. Comparison of this trend to radiative transfer models and various results from literature suggests that these high-redshift Ly{\alpha} emitters are not likely to be intrinsically round and symmetric disks, but they probably host galactic outflows traced by Ly{\alpha} emitting clouds. The ionizing sources are centrally located, with the optical depth a good indicator of the absorption and scattering events on the escape path of Ly{\alpha} photons from the source. Our results find no evidence for evolution in Ly{\alpha} asymmetry or axial ratio with look-back time.
Many features of the outer solar system are replicated in numerical simulations if the giant planets undergo an orbital instability that ejects one or more ice giants. During this instability, Jupiter and Saturn's orbits diverge, crossing their 2:1 mean motion resonance (MMR), and this resonance-crossing can excite the terrestrial planet orbits. Using a large ensemble of simulations of this giant planet instability, we directly model the evolution of the terrestrial planet orbits during this process, paying special attention to systems that reproduce the basic features of the outer planets. In systems that retain four giant planets and finish with Jupiter and Saturn beyond their 2:1 MMR, we find at least an 85% probability that at least one terrestrial planet is lost. Moreover, systems that manage to retain all four terrestrial planets often finish with terrestrial planet eccentricities and inclinations larger than the observed ones. There is less than a ~5% chance that the terrestrial planet orbits will have a level of excitation comparable to the observed orbits. If we factor in the probability that the outer planetary orbits are well-replicated, we find a probability of 1% or less that the orbital architectures of the inner and outer planets are simultaneously reproduced in the same system. These small probabilities raise the prospect that the giant planet instability occurred before the terrestrial planets had formed. This scenario implies that the giant planet instability is not the source of the Late Heavy Bombardment and that terrestrial planet formation finished with the giant planets in their modern configuration.
An understanding of the mass build-up in galaxies over time necessitates tracing the evolution of cold gas (molecular and atomic) in galaxies. To that end, we have conducted a pilot study called CO Observations with the LMT of the Blind Ultra-Deep H I Environment Survey (COOL BUDHIES). We have observed 23 galaxies in and around the two clusters Abell 2192 (z = 0.188) and Abell 963 (z = 0.206), where 12 are cluster members and 11 are slightly in the foreground or background, using about 28 total hours on the Redshift Search Receiver (RSR) on the Large Millimeter Telescope (LMT) to measure the $^{12}$CO J = 1 --> 0 emission line and obtain molecular gas masses. These new observations provide a unique opportunity to probe both the molecular and atomic components of galaxies as a function of environment beyond the local Universe. For our sample of 23 galaxies, nine have reliable detections (S/N$\geq$3.6) of the $^{12}$CO line, and another six have marginal detections (2.0 < S/N < 3.6). For the remaining eight targets we can place upper limits on molecular gas masses roughly between $10^9$ and $10^{10} M_\odot$. Comparing our results to other studies of molecular gas, we find that our sample is significantly more abundant in molecular gas overall, when compared to the stellar and the atomic gas component, and our median molecular gas fraction lies about $1\sigma$ above the upper limits of proposed redshift evolution in earlier studies. We discuss possible reasons for this discrepancy, with the most likely conclusion being target selection and Eddington bias.
In recent years there have been many attempts to characterize the occurrence of stellar, BD and planetary-mass companions to solar-type stars, with the aim of constraining formation mechanisms. From RV observations a dearth of companions with masses between 10-40 MJup has been noticed at close separations, suggesting the possibility of a distinct formation mechanism for objects above and below this range. We present a model for the substellar companion mass function (CMF). It consists of the superposition of the planet and BD companion mass distributions, assuming that we can extrapolate the RV measured companion mass function for planets to larger separations and the stellar companion mass-ratio distribution over all separations into the BD mass regime. By using both the results of the VLT/NaCo large program and the complementary archive datasets that probe the occurrence of planets and BDs on wide orbits around solar-type stars, we place some constraints on the planet and BD distributions. We developed a MC simulation tool to predict the outcome of a given survey, depending on the shape of the orbital parameter distributions. Comparing the predictions with the results of the observations, we calculate how likely different models are and which can be ruled out. Current observations are consistent with the proposed model for the CMF, as long as a sufficiently small outer truncation radius is introduced for the planet separation distribution. The results of the direct imaging surveys searching for substellar companions around Sun-like stars are consistent with a combined substellar mass spectrum of planets and BDs. This mass distribution has a minimum between 10 and 50 MJup, in agreement with RV measurements. The dearth of objects in this mass range would naturally arise from the shape of the mass distribution, without the introduction of any distinct formation mechanism for BDs.
Observations of luminous flares resulting from the possible tidal disruption of stars by supermassive black holes have raised a number of puzzles. Outstanding questions include the origin of the optical and ultraviolet (UV) flux, the weakness of hydrogen lines in the spectrum, and the occasional simultaneous observation of x-rays. Here we study the emission from tidal disruption events (TDEs) produced as radiation from black hole accretion propagates through an extended, optically thick envelope formed from stellar debris. We analytically describe key physics controlling spectrum formation, and present detailed radiative transfer calculations that model the spectral energy distribution (SED) and optical line strengths of TDEs near peak brightness. The steady-state transfer is coupled to a non local thermodynamic equilibrium treatment of the excitation and ionization states of hydrogen, helium and oxygen (as a representative metal). Our calculations show how an extended envelope can reprocess a fraction of soft x-rays and produce the observed optical fluxes of order 10^43 ergs per second. Variations in the mass or size of the envelope may help explain how the optical flux changes over time with roughly constant color. For high enough accretion luminosities, x-rays can highly ionize the reprocessing region and escape to be observed simultaneously with the optical flux, producing an SED not described by a single blackbody. Due to optical depth effects, hydrogen Balmer line emission is often strongly suppressed relative to helium line emission (with HeII-to-H line ratios of at least 5:1 in some cases) even in the disruption of a solar-composition star. We discuss the implications of our results to understanding the type of stars destroyed in TDEs and the physical processes responsible for producing the observed flares.
Based on data from the ongoing OGLE Galaxy Variability Survey (OGLE GVS) we have verified observed properties of stars detected by the near-infrared VVV survey in a direction near the Galactic plane at longitude l~-27 deg and recently tentatively classified as classical Cepheids belonging to a, hence claimed, dwarf galaxy at a distance of about 90 kpc from the Galactic Center. Three of four stars are detected in the OGLE GVS I-band images. We show that two of the objects are not variable at all and the third one with a period of 5.695 d and a nearly sinusoidal light curve of an amplitude of 0.5 mag cannot be a classical Cepheid and is very likely a spotted object. These results together with a very unusual shape of the Ks-band light curve of the fourth star indicate that very likely none of them is a Cepheid and, thus, there is no evidence for a background dwarf galaxy. Our observations show that a great care must be taken when classifying objects by their low-amplitude close-to-sinusoidal near-infrared light curves, especially with a small number of measurements. We also provide a sample of high-amplitude spotted stars with periods of a few days that can mimick pulsations and even eclipses.
The role of gravitational instability-driven turbulence in determining the structure and evolution of disk galaxies, and the extent to which gravity rather than feedback can explain galaxy properties, remains an open question. To address it, we present high resolution adaptive mesh refinement simulations of Milky Way-like isolated disk galaxies, including realistic heating and cooling rates and a physically motivated prescription for star formation, but no form of star formation feedback. After an initial transient, our galaxies reach a state of fully-nonlinear gravitational instability. In this state, gravity drives turbulence and radial inflow. Despite the lack of feedback, the gas in our galaxy models shows substantial turbulent velocity dispersions, indicating that gravitational instability alone may be able to power the velocity dispersions observed in nearby disk galaxies on 100 pc scales. Moreover, the rate of mass transport produced by this turbulence approaches $\sim 1$ $M_\odot$ yr$^{-1}$ for Milky Way-like conditions, sufficient to fully fuel star formation in the inner disks of galaxies. In a companion paper we add feedback to our models, and use the comparison between the two cases to understand what galaxy properties depend sensitively on feedback, and which can be understood as the product of gravity alone. All of the code, initial conditions, and simulation data for our model are publicly available.
We analyse the environment of the supermassive black hole (SMBH) in the centre of a massive elliptical galaxy NGC 1275 in the Perseus cluster, hosting the radio source 3C 84. We focus on the young radio lobe observed inside the estimated Bondi accretion radius. We discuss the momentum balance between the jet associated with the lobe and the surrounding gas. The results are compared with the proper motion of the radio lobe obtained with the VLBI. We find that under assumption of a high-density environment >~ 100 cm^-3), the jet power must be comparable to the Eddington luminosity --- this is clearly inconsistent with the current moderate activity of 3C 84, which indicates instead that the jet is expanding in a very low density region (<~1 cm^-3), along the rotation axis of the accretion flow. The power required for the jet to expand in the low-density environment is comparable to the past average jet power estimated from the X-ray observations. We estimate the classical Bondi accretion rate, assuming that (1) gas accretion is spherically symmetric, (2) accretion is associated with the jet environment, and (3) the medium surrounding the jet is representative of the properties of the dominant accreting gas. We find that Bondi accretion is inconsistent with the estimated jet power. This means that either accretion of the cold gas in the NGC 1275 is more efficient than that of the hot gas, or the jets are powered by the SMBH spin.
The most frequently proposed model for the origin of quasars holds that the high accretion rates seen in luminous active galactic nuclei are primarily triggered during major mergers between gas-rich galaxies. While plausible for decades, this model has only begun to be tested with statistical rigor in the past few years. Here we report on a Hubble Space Telescope study to test the merger-triggering hypothesis for $z=2$ quasars with high super-massive black hole masses ($M_\mathrm{BH}=10^9-10^{10}~M_\odot{}$), which dominate cosmic black hole growth at this redshift. We compare Wide Field Camera 3 $F160W$ (rest-frame $V$-band) imaging of 19 point source-subtracted quasar hosts to a matched sample of 84 inactive galaxies, testing whether the quasar hosts have a statistically higher fraction of strong gravitational interaction signatures. We recover strong distortion fractions of $f_\mathrm{m,qso}=0.39\pm{}0.11$ for the quasar hosts and $f_\mathrm{m,gal}=0.30\pm{}0.05$ for the inactive galaxies (distribution modes, 68\% confidence intervals), with both measurements subjected to the same observational conditions and limitations. We definitively rule out both extreme cases (all mergers, no mergers) for the quasar host population. The slight observed enhancement in merger signatures for quasar hosts over inactive galaxies is not statistically significant, with a probability that the quasar fraction is higher of $P(f_\mathrm{m,qso}>f_\mathrm{m,gal}) = 0.78$ ($0.78\,\sigma$), in line with results for lower mass and lower $z$ AGN. We thus find no evidence that major mergers are the primary triggering mechanism for the massive active galactic nuclei that dominate accretion at the peak of cosmic quasar activity.
We present an analysis of the predictions made by the Galform semi-analytic galaxy formation model for the evolution of the relationship between stellar mass and halo mass. We show that for the standard implementations of supernova feedback and gas reincorporation used in semi-analytic models, this relationship is predicted to evolve weakly over the redshift range 0<z<4. Modest evolution in the median stellar mass versus halo mass (SHM) relationship implicitly requires that, at fixed halo mass, the efficiency of stellar mass assembly must be almost constant with cosmic time. We show that in our model, this behaviour can be understood in simple terms as a result of a constant efficiency of gas reincorporation, and an efficiency of SNe feedback that is, on average, constant at fixed halo mass. We present a simple explanation of how feedback from active galactic nuclei (AGN) acts in our model to introduce a break in the SHM relation whose location is predicted to evolve only modestly. Finally, we show that if modifications are introduced into the model such that, for example, the gas reincorporation efficiency is no longer constant, the median SHM relation is predicted to evolve significantly over 0<z<4. Specifically, we consider modifications that allow the model to better reproduce either the evolution of the stellar mass function or the evolution of average star formation rates inferred from observations.
We present first results from a targeted search for brown dwarfs with unusual red colors indicative of peculiar atmospheric characteristics. These include objects with low surface gravities or with unusual dust content or cloud properties. From a positional cross-match of SDSS, 2MASS and WISE, we have identified 40 candidate peculiar early L to early T dwarfs that are either new objects or have not been identified as peculiar through prior spectroscopy. Using low resolution spectra, we confirm that 10 of the candidates are either peculiar or potential L/T binaries. With a J-Ks color of 2.62 +/- 0.15 mag, one of the new objects --- the L7 dwarf 2MASS J11193254-1137466 --- is among the reddest field dwarfs currently known. Its proper motion and photometric parallax indicate that it is a possible member of the TW Hydrae moving group. If confirmed, it would its lowest-mass (5--6 MJup) free-floating member. We also report a new T dwarf, 2MASS J22153705+2110554, that was previously overlooked in the SDSS footprint. These new discoveries demonstrate that despite the considerable scrutiny already devoted to the SDSS and 2MASS surveys, our exploration of these data sets is not yet complete.
In the last few years, it became possible to observationally resolve galaxies with two distinct nuclei in their centre. For separations smaller than 10kpc, dual and offset active galactic nuclei (AGN) are distinguished: in dual AGN, both nuclei are active, whereas in offset AGN only one nucleus is active. To theoretically study the origin of such AGN pairs, we employ a cosmological, hydrodynamic simulation with a large volume of (182 Mpc)^3 from the set of Magneticum Pathfinder Simulations. The simulation self-consistently produces 35 resolved black hole (BH) pairs at redshift z=2, with a comoving distance smaller than 10kpc. 14 of them are offset AGN and nine are dual AGN, resulting in a fraction of (1.2 \pm 0.3)% AGN pairs with respect to the total number of AGN. In this paper, we discuss fundamental differences between the BH and galaxy properties of dual AGN, offset AGN and inactive BH pairs and investigate their different triggering mechanisms. We find that in dual AGN, the corresponding BH from the less massive progenitor galaxy always accretes with a higher Eddington ratio and that dual AGN have similar BH masses. In contrast, in offset AGN, the active BH is typically more massive than its non-active counterpart. Furthermore, dual AGN in general accrete more gas from the intergalactic medium than offset AGN and non-active BH pairs. This highlights that merger events, particularly minor mergers, do not necessarily lead to strong gas inflows and thus, do not always drive strong nuclear activity.
Pulsar timing arrays (PTAs) are placing increasingly stringent constraints on the strain amplitude of continuous gravitational waves emitted by supermassive black hole binaries on subparsec scales. In this paper, we incorporate independent measurements of the dynamical masses $M_{\rm bh}$ of supermassive black holes in specific galaxies at known distances and leverage this additional information to further constrain whether or not those galaxies could host a detectable supermassive black hole binary. We estimate the strain amplitudes from individual binaries as a function of binary mass ratio for two samples of nearby galaxies: (1) those with direct dynamical measurements of $M_{\rm bh}$ in the literature, and (2) the 116 most massive early-type galaxies (and thus likely hosts of the most massive black holes) within 108 Mpc from the MASSIVE Survey. Our exploratory analysis shows that the current PTA upper limits on continuous waves can already constrain the mass ratios of hypothetical black hole binaries in a dozen galaxies in our samples. The constraints are stronger for galaxies with larger $M_{\rm bh}$ and at smaller distances. For the black holes with $M_{\rm bh} \gtrsim 5\times 10^9 M_\odot$ at the centers of NGC 4889, NGC 4486 (M87) and NGC 4649 (M60), any binary companion in orbit within the PTA frequency bands would have to have a mass ratio of less than about 1:10.
Most star clusters at an intermediate age (1-2 Gyr) in the Large and Small Magellanic Clouds show a puzzling feature in their color-magnitude diagrams (CMD) that is not in agreement with a simple stellar population. The main sequence turn-off of these clusters is much broader than would be expected from photometric uncertainties. One interpretation of this feature is that age spreads of the order 200-500 Myr exist within individual clusters, although this interpretation is highly debated. Such large age spreads should affect other parts of the CMD, which are sensitive to age, as well. In this study, we analyze the CMDs of a sample of 12 intermediate-age clusters in the Large Magellanic Cloud that all show an extended turn-off using archival optical data taken with the Hubble Space Telescope. We fit the star formation history of the turn-off region and the red clump region independently with two different theoretical isochrone models. We find that in most of the cases, the age spreads inferred from the red clumps are smaller than the ones resulting from the turn-off region. However, the age ranges resulting from the red clump region are broader than would be expected for a single age. Only two out of 12 clusters in our sample show a red clump which seems to be consistent with a single age. As our results are not unambiguous, we can not ultimately tell if the extended main sequence turn-off feature is due to an age spread, or not, by fitting the star formation histories to the red clump regions. However, we find that the width of the extended main sequence turn-off feature is correlated with the age of the clusters in a way which would be unexplained in the "age spread" interpretation, but which may be expected if stellar rotation is the cause of the spread at the turn-off.
Sub-virial gravitational collapse is one mechanism by which star clusters may form. Here we investigate whether this mechanism can be inferred from observations of young clusters. To address this question, we have computed SPH simulations of the initial formation and evolution of a dynamically young star cluster through cold (sub-virial) collapse, starting with an ellipsoidal, turbulently seeded distribution of gas, and forming sink particles representing (proto)stars. While the initial density distributions of the clouds do not have large initial mass concentrations, gravitational focusing due to the global morphology leads to cluster formation. We use the resulting structures to extract observable morphological and kinematic signatures for the case of sub-virial collapse. We find that the signatures of the initial conditions can be erased rapidly as the gas and stars collapse, suggesting that kinematic observations need to be made either early in cluster formation and/or at larger scales, away from the growing cluster core. Our results emphasize that a dynamically young system is inherently evolving on short timescales, so that it can be highly misleading to use current-epoch conditions to study aspects such as star formation rates as a function of local density. Our simulations serve as a starting point for further studies of collapse including other factors such as magnetic fields and stellar feedback.
Quantifying the concordance between different cosmological experiments is important for testing the validity of theoretical models and systematics in the observations. In earlier work, we thus proposed the Surprise, a concordance measure derived from the relative entropy between posterior distributions. We revisit the properties of the Surprise and describe how it provides a general, versatile, and robust measure for the agreement between datasets. We also compare it to other measures of concordance that have been proposed for cosmology. As an application, we extend our earlier analysis and use the Surprise to quantify the agreement between WMAP 9, Planck 13 and Planck 15 constraints on the $\Lambda$CDM model. Using a principle component analysis in parameter space, we find that the large Surprise between WMAP 9 and Planck 13 (S = 17.6 bits, implying a deviation from consistency at 99.8% confidence) is due to a shift along a direction that is dominated by the amplitude of the power spectrum. The Surprise disappears when moving to Planck 15 (S = -5.1 bits). This means that, unlike Planck 13, Planck 15 is not in tension with WMAP 9. These results illustrate the advantages of the relative entropy and the Surprise for quantifying the disagreement between cosmological experiments and more generally as an information metric for cosmology.
Recent discoveries of circumbinary planets in Kepler data show that there is a viable channel of planet formation around binary main sequence stars. Motivated by these discoveries, we have investigated the caustic structures and detectability of circumbinary planets in microlensing events. We have produced a suite of animations of caustics as a function of the projected separation and angle of the binary host to efficiently explore caustic structures over the entire circumbinary parameter space. Aided by these animations, we have derived a semi-empirical analytic expression for the location of planetary caustics, which are displaced in circumbinary lenses relative to those of planets with a single host. We have used this expression to show that the dominant source of caustic motion will be due to the planet's orbital motion and not that of the binary star. Finally, we estimate the fraction of circumbinary microlensing events that are recognizable as such to be significant (5-50 percent) for binary projected separations in the range 0.1-0.5 in units of Einstein radii.
We present Ks-band light curves for 299 new Cepheids in the Small Magellanic Cloud (SMC) that were identified using multi-epoch near-infrared photometry obtained by the VISTA survey of the Magellanic Clouds system (VMC). The new Cepheids have periods in the range from 0.38 to 13.15 days and cover the magnitude interval 12.35 < Ks < 17.6 mag. Our method was developed using variable stars previously identified by the optical microlensing survey OGLE. We focus on searching new Cepheids in external regions of the SMC for which complete VMC Ks-band observations are available and no comprehensive identification of different types of variable stars from other surveys exists yet.
We explore a time-dependent energy dissipation of the energetic electrons in the inhomogeneous intergalactic medium (IGM) during the epoch of cosmic reionization. In addition to the atomic processes we take into account the Inverse Compton (IC) scattering of the electrons on the comic microwave background (CMB) photons, which is the dominant channel of energy loss for the electrons with energies above a few MeV. We show that: (1) the effect on the IGM has both local (atomic processes) and non-local (IC radiation) components; (2) the energy distribution between Hydrogen and Helium ionizations depends on the initial electron energy; (3) the local baryon overdensity significantly affects the fractions of energy distributed in each channel; and (4) the relativistic effect of atomic cross section become important during the epoch of cosmic reionization. We release our code as open source for further modification by the community.
We analyze the resolved stellar populations of the faint stellar system, Crater, based on deep optical imaging taken with the Hubble Space Telescope. The HST/ACS-based color-magnitude diagram (CMD) of Crater extends $\sim$4 magnitudes below the oldest main sequence turnoff, providing excellent leverage on Crater's physical properties. Structurally, Crater has a half-light radius of $\sim$20 pc and shows no evidence for tidal distortions. Crater is well-described by a simple stellar population with an age of $\sim$7.5 Gyr, [M/H]$\sim-1.65$, a M$_{\star}\sim10^4$ M$_{\odot}$, M$_{\rm V}\sim -5.3$, located at a distance of (d$_{\odot}$, d$_{\rm GC}$) $\sim$ (145, 110) kpc, with modest uncertainties in these properties due to differences in the underlying stellar evolution models. The sparse sampling of stars above the turnoff and sub-giant branch are likely to be 1.0-1.4 M$_{\odot}$ binary star systems (blue stragglers) and their evolved descendants, as opposed to intermediate age main sequence stars. Confusion of these populations highlights a substantial challenge in accurately characterizing sparsely populated stellar systems. Our analysis shows that Crater is not a dwarf galaxy, but instead is an unusually young cluster given its location in the Milky Way's very outer stellar halo. Crater is similar to SMC cluster Lindsay 38, and its position and velocity are in good agreement with observations and models of the Magellanic stream debris, suggesting it may have accreted from the Magellanic Clouds. However, its age and metallicity are also in agreement with the age-metallicity relationships of lower mass dwarf galaxies such as Leo I or Carina. Despite uncertainty over its progenitor system, Crater appears to have been incorporated into the Galaxy more recently than $z\sim1$ (8 Gyr ago), providing an important new constraint on the accretion history of the Milky Way. [abridged]
The study of supernova remnants (SNRs) is fundamental to understanding the chemical enrichment and magnetism in galaxies, including our own Milky Way. In an effort to understand the connection between the morphology of SNRs and the Galactic magnetic field (GMF), we have examined the radio images of all known SNRs in our Galaxy and compiled a large sample that have an "axisymmetric" morphology, which we define to mean SNRs with a "bilateral" or "barrel"-shaped morphology, in addition to one-sided shells. We selected the cleanest examples and model each of these at their appropriate Galactic position using two GMF models, those of Jansson & Farrar (2012a), which includes a vertical halo component, and Sun et al. (2008) that is oriented entirely parallel to the plane. Since the magnitude and relative orientation of the magnetic field changes with distance from the sun, we analyse a range of distances, from 0.5 to 10 kpc in each case. Using a physically motivated model of a SNR expanding into the ambient GMF, we find the models using Jansson & Farrar (2012a) are able to reproduce observed morphologies of many SNRs in our sample. These results strongly support the presence of an off-plane, vertical component to the GMF, and the importance of the Galactic field on SNR morphology. Our approach also provides a potential new method for determining distances to SNRs, or conversely, distances to features in the large-scale GMF if SNR distances are known.
I address uncertainties on the spatial distribution and mass of the dust formed in $\eta$ Carinae's Homunculus nebula with data being combined from several space- and ground-based facilities spanning near-infrared to sub-mm wavelengths, in terms of observational constraints and modeling. Until these aspects are better understood, the mass loss history and mechanisms responsible for $\eta$ Car's enormous eruption(s) remain poorly constrained.
We report a spin-orbit misalignment for the hot-Jupiter HATS-14b, measuring a projected orbital obliquity of |lambda|= 76 -5/+4 deg. HATS-14b orbits a high metallicity, 5400 K G dwarf in a relatively short period orbit of 2.8 days. This obliquity was measured via the Rossiter-McLaughlin effect, obtained with observations from Keck-HIRES. The velocities were extracted using a novel technique, optimised for low signal-to-noise spectra, achieving a high precision of 4 m/s point-to-point scatter. However, we caution that our uncertainties may be underestimated. Due to the low rotational velocity of the star, the detection significance is dependent on the vsini prior that is imposed in our modelling. Based on trends observed in the sample of hot Jupiters with obliquity measurements, it has been suggested that these planets modify the spin axes of their host stars, with an efficiency that depends on the stellar type and orbital period of the system. In this framework, short-period planets around stars with surface convective envelopes, like HATS-14b, are expected to have orbits that are aligned with the spin axes of their host stars. HATS-14b, however, is a significant outlier from this trend, challenging the effectiveness of the tidal realignment mechanism.
The collapse of the primordial gas in the density regime $\sim 10^{8}\hbox{--}10^{10}$ cm$^{-3}$ is controlled by the three-body $\rm H_2$ formation process, in which the gas can cool faster than free-fall time $\hbox{--}$ a condition proposed as the chemothermal instability. We investigate how the heating and cooling rates are affected during the rapid transformation of atomic to molecular hydrogen. With a detailed study of the heating and cooling balance in a 3D simulation of Pop~III collapse, we follow the chemical and thermal evolution of the primordial gas in two dark matter minihaloes. The inclusion of sink particles in modified Gadget-2 smoothed particle hydrodynamics code allows us to investigate the long term evolution of the disk that fragments into several clumps. We find that the sum of all the cooling rates is less than the total heating rate after including the contribution from the compressional heating ($pdV$). The increasing cooling rate during the rapid increase of the molecular fraction is offset by the unavoidable heating due to gas contraction. We conclude that fragmentation occurs because $\rm H_2$ cooling, the heating due to $\rm H_2$ formation and compressional heating together set a density and temperature structure in the disk that favors fragmentation, not the chemothermal instability.
Ultra luminous X-ray sources (ULXs) are usually believed to be black holes with mass about 10^{2--3}M_{sun}. However, the recent discovery of ULX NuSTAR J095551+6940.8 in M82 with the spin period P=1.37s and period derivation P_{dot}=-2*10^{-10} ss^{-1} provides a strong evidence that some ULXs are accreting neutron stars (NSs). To investigate such a particular accreting neutron star, we ascribe it as an evolved magnetar in the accretion binary system. By means of the model of accretion induced the NS magnetic evolution and standard spinup torque, we calculate the magnetic field decay and spin-up of M82 X-2, and show that its magnetic field is now 4.5*10^{12} G, which is evolved from a magnetar in a high mass Xray binary system (HMXB) with the initial values of magnetic field B~10^{14.5} G and spin period P~100 s by accreting ~10^{-3}M_{sun}, while the mass accretion rate for spin-up is set as 5.0*10^{18} gs^{-1}. The evolutionary track of magnetic field and spin period of M82 X-2 is simulated and plotted in the B-P diagram, with which we compare the observed pulsars, and find that several pulsars are consistent with the B-P track of M82 X-2. Since the birth rate of magnetar is about ten percent of the normal NSs, it is inferred that a couple of ULXs should also be the similar cases like M82 X-2. Furthermore, we argue that the existence of the local super-strong magnetic multipole structure of M82 X-2 destroys the spherical accretion condition of Eddington critical luminosity, which arises the ULX M82 X-2 to be different from the usual NS in HMXBs with the luminosity no more than the Eddington limit ......
Isolated magnetic white dwarfs have field strengths ranging from kilogauss to gigagauss, and constitute an interesting class of objects. The origin of the magnetic field is still the subject of a hot debate. Whether these fields are fossil, hence the remnants of original weak magnetic fields amplified during the course of the evolution of the progenitor of white dwarfs, or on the contrary, are the result of binary interactions or, finally, other physical mechanisms that could produce such large magnetic fields during the evolution of the white dwarf itself, remains to be elucidated. In this work we review the current status and paradigms of magnetic fields in white dwarfs, from both the theoretical and observational points of view.
Asteroseismology allows for deriving precise values of surface gravity of stars. The accurate asteroseismic determinations now available for large number of stars in the Kepler fields can be used to check and calibrate surface gravities that are currently being obtained spectroscopically for a huge numbers of stars targeted by large-scale spectroscopic surveys, such as the on-going Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Galactic survey. The LAMOST spectral surveys have obtained a large number of stellar spectra in the Kepler fields. Stellar atmospheric parameters of those stars have been determined with the LAMOST Stellar Parameter Pipeline at Peking University (LSP3), by template matching with the MILES empirical spectral library. In the current work, we compare surface gravities yielded by LSP3 with those of two asteroseismic samples - the largest sample from Huber et al. (2014) and the most accurate sample from Hekker et al. (2012, 2013). We find that LSP3 surface gravities are in good agreement with asteroseismic values of Hekker et al. (2012, 2013), with a dispersion of about 0.2 dex. Except for a few cases, asteroseismic surface gravities of Huber et al. (2014) and LSP3 spectroscopic values agree for a wide range of surface gravities. However, some patterns of differences can be identified upon close inspection. Potential ways to further improve the LSP3 spectroscopic estimation of stellar atmospheric parameters in the near future are briefly discussed. The effects of effective temperature and metallicity on asteroseismic determinations of surface gravities for giant stars are also discussed.
Theoretical studies have revealed that dust grains are usually moving fast through the turbulent interstellar gas, which could have significant effects upon molecular cloud chemistry by modifying grain accretion. This effect is investigated in this work on the basis of numerical gas-grain chemical modeling. Major features of the grain motion effect in the typical environment of dark clouds (DC) can be summarised as follows: 1) decrease of gas-phase (both neutral and ionic) abundances and increase of surface abundances by up to 2-3 orders of magnitude; 2) shifts of the existing chemical jumps to earlier evolution ages for gas-phase species and to later ages for surface species by factors of about ten; 3) a few exceptional cases in which some species turn out to be insensitive to this effect and some other species can show opposite behaviors too. These effects usually begin to emerge from a typical DC model age of about 10^5 yr. The grain motion in a typical cold neutral medium (CNM) can help overcome the Coulomb repulsive barrier to enable effective accretion of cations onto positively charged grains. As a result, the grain motion greatly enhances the abundances of some gas-phase and surface species by factors up to 2-6 or more orders of magnitude in the CNM model. The grain motion effect in a typical molecular cloud (MC) is intermediate between that of the DC and CNM models, but with weaker strength. The grain motion is found to be important to consider in chemical simulations of typical interstellar medium.
The increasing number of Very High Energy (VHE) sources discovered by the current generation of Cherenkov telescopes made particularly relevant the creation of a dedicated source catalogs as well as the cross-correlation of VHE and lower energy bands data in a multi-wavelength framework. The "TeGeV Catalog" hosted at the ASI Science Data Center (ASDC) is a catalog of VHE sources detected by ground-based Cherenkov detectors. The TeGeVcat collects all the relevant information publicly available about the observed GeV/TeV sources. The catalog contains also information about public light curves while the available spectral data are included in the ASDC SED Builder tool directly accessible from the TeGeV catalog web page. In this contribution we will report a comprehensive description of the catalog and the related tools.
We have used the Arecibo L-band Feed Array to map three regions, each of 5 square degrees, around the isolated galaxies NGC 1156, UGC 2082, and NGC 5523. In the vicinity of these galaxies we have detected two dwarf companions: one near UGC 2082, previously discovered by ALFALFA, and one near NGC 1156, discovered by this project and reported in an earlier paper. This is significantly fewer than the 15.4 $^{+1.7}_{-1.5}$ that would be expected from the field HI mass function from ALFALFA or the 8.9 $\pm$ 1.2 expected if the HI mass function from the Local Group applied in these regions. The number of dwarf companions detected is, however, consistent with a flat or declining HI mass function as seen by a previous, shallower, HI search for companions to isolated galaxies.We attribute this difference in Hi mass functions to the different environments in which they are measured. This agrees with the general observation that lower ratios of dwarf to giant galaxies are found in lower density environments.
Recently, we have shown that the propagation speed $c_T$ of the primordial gravitational waves (GWs) might be nontrivially varying during inflation, which could induce local oscillations in the power spectrum of primordial GWs. In this paper, we numerically confirm that, although with a disformal redefinition of the metric the nontrivial $c_T$ may be set as unity, the power spectrum in the frame with $c_T=1$ is completely same with that in the original disformal frame, i.e., the oscillating shape in the power spectrum is still reserved, since here the effect of $c_T$ is actually encoded in the nontrivially varying Hubble parameter. In addition, we also clarify how obtaining a blue-tilt GWs spectrum by imposing a rapidly decreasing $c_T$ during inflation.
Recent atomic physics calculations for Si II are employed within the Cloudy modelling code to analyse Hubble Space Telescope (HST) STIS ultraviolet spectra of three cool stars, Beta-Geminorum, Alpha-Centauri A and B, as well as previously published HST/GHRS observations of Alpha-Tau, plus solar quiet Sun data from the High Resolution Telescope and Spectrograph. Discrepancies found previously between theory and observation for line intensity ratios involving the 3s$^{2}$3p $^{2}$P$_{J}$--3s3p$^{2}$ $^{4}$P$_{J^{\prime}}$ intercombination multiplet of Si II at 2335 Angs are significantly reduced, as are those for ratios containing the 3s$^{2}$3p $^{2}$P$_{J}$--3s3p$^{2}$ $^{2}$D$_{J^{\prime}}$ transitions at 1816 Angs. This is primarily due to the effect of the new Si II transition probabilities. However, these atomic data are not only very different from previous calculations, but also show large disagreements with measurements, specifically those of Calamai et. al. (1993) for the intercombination lines. New measurements of transition probabilities for Si II are hence urgently required to confirm (or otherwise) the accuracy of the recently calculated values. If the new calculations are confirmed, then a long-standing discrepancy between theory and observation will have finally been resolved. However, if the older measurements are found to be correct, then the agreement between theory and observation is simply a coincidence and the existing discrepancies remain.
We aim to study the influence of radiative cooling on the standing kink oscillations of a coronal loop. Using the FLASH code, we solved the 3D ideal magnetohydrodynamic equations. Our model consists of a straight, density enhanced and gravitationally stratified magnetic flux tube. We perturbed the system initially, leading to a transverse oscillation of the structure, and followed its evolution for a number of periods. A realistic radiative cooling is implemented. Results are compared to available analytical theory. We find that in the linear regime (i.e. low amplitude perturbation and slow cooling) the obtained period and damping time are in good agreement with theory. The cooling leads to an amplification of the oscillation amplitude. However, the difference between the cooling and non-cooling cases is small (around 6% after 6 oscillations). In high amplitude runs with realistic cooling, instabilities deform the loop, leading to increased damping. In this case, the difference between cooling and non-cooling is still negligible at around 12%. A set of simulations with higher density loops are also performed, to explore what happens when the cooling takes place in a very short time (tcool = 100 s). We strengthen the results of previous analytical studies that state that the amplification due to cooling is ineffective, and its influence on the oscillation characteristics is small, at least for the cases shown here. Furthermore, the presence of a relatively strong damping in the high amplitude runs even in the fast cooling case indicates that it is unlikely that cooling could alone account for the observed, flare-related undamped oscillations of coronal loops. These results may be significant in the field of coronal seismology, allowing its application to coronal loop oscillations with observed fading-out or cooling behaviour.
We explore the mean and fluctuating redshifted 21 cm signal in numerical simulations of cosmic reionization from the Cosmic Reionization On Computers (CROC) project. We find that the mean signal varies between about $\pm20\rm{mK}$. Most significantly, we find that the negative pre-reionization dip at $z\sim10-15$ only extends to $\langle\Delta T_B\rangle\sim-20\rm{mK}$, in agreement with prior simulation results and in significant contrast to Pritchard & Loeb analytical model, requiring substantially higher sensitivity from global signal experiments that operate in this redshift range (EDGES-II, LEDA, SCI-HI, and DARE). We also explore the role of dense substructure (filaments and embedded galaxies) in the formation of 21 cm power spectrum. We find that by neglecting the semi-neutral substructure inside ionized bubbles, the power spectrum can be mis-estimated by 25-50\% at scales $k\sim 0.1-1h\rm{Mpc}^{-1}$. This scale range is of a particular interest, because the upcoming 21 cm experiments (MWA, PAPER, HERA) are expected to be most sensitive within it.
The simplest two-field completion of natural inflation has a regime in which both fields are active and in which its predictions are within the Planck 1-$\sigma$ confidence contour. We show this for the original model of natural inflation, in which inflation is achieved through the explicit breaking of a U(1) symmetry. We consider the case in which the mass coming from explicit breaking of this symmetry is comparable to that from spontaneous breaking, which we show is consistent with a hierarchy between the corresponding energy scales. While both masses are comparable when the observable modes left the horizon, the mass hierarchy is restored in the last e-foldings of inflation, rendering the predictions consistent with the isocurvature bounds. For completeness, we also study the predictions for the case in which there is a large hierarchy of masses and an initial period of inflation driven by the (heavy) radial field.
In recent years several small basaltic V-type asteroids have been identified all around the main belt. Most of them are members of the Vesta dynamical family, but an increasingly large number appear to have no link with it. The question that arises is whether all these basaltic objects do indeed come from Vesta. To find the answer to the above questioning, we decided to perform a statistical analysis of the spectroscopic and mineralogical properties of a large sample of V-types, with the objective to highlight similarities and differences among them, and shed light on their unique, or not, origin. The analysis was performed using 190 visible and near-infrared spectra from the literature for 117 V-type asteroids. The asteroids were grouped according to their dynamical properties and their computed spectral parameters compared. Comparison was also performed with spectral parameters of a sample of HED meteorites and data of the surface of Vesta taken by the VIR instrument on board of the Dawn spacecraft. Our analysis shows that although most of the V-type asteroids in the inner main belt do have a surface composition compatible with an origin from Vesta, this seem not to be the case for V-types in the middle and outer main belt.
We show that the Cosmic Microwave Background can be used to measure our peculiar velocity in a novel way, by looking at Doppler-induced distortions of the intensity blackbody spectrum which couple different multipoles. The frequency dependence of such a signal is called y-type, and is degenerate with the thermal SZ (tSZ) effect. Interestingly, like the kinetic Doppler quadrupole, its measurement is not limited by cosmic variance of the temperature spectrum; instead it only depends on experimental noise and on the small contamination due to the tSZ effect. Already with Planck this method yields a signal-to-noise ratio of about 9, and future experiments can increase this to somewhere around 15-40, and in principle even further if tSZ effect can be subtracted using data from clusters. Such a signal is present at all multipoles, but mostly in ell <~ 400, providing thus an independent way to measure our velocity that might also clarify the mixing between Doppler and a possible anomalous intrinsic dipolar modulation of the CMB spectrum, which seems to be present in temperature data at large scales.
We extend a general maximum likelihood foreground estimation for cosmic microwave background polarization data to include estimation of instrumental systematic effects. We focus on two particular effects: frequency band measurement uncertainty, and instrumentally induced frequency dependent polarization rotation. We assess the bias induced on the estimation of the $B$-mode polarization signal by these two systematic effects in the presence of instrumental noise and uncertainties in the polarization and spectral index of Galactic dust. Degeneracies between uncertainties in the band and polarization angle calibration measurements and in the dust spectral index and polarization increase the uncertainty in the extracted CMB $B$-mode power, and may give rise to a biased estimate. We provide a quantitative assessment of the potential bias and increased uncertainty in an example experimental configuration. For example, we find that with 10\% polarized dust, tensor to scalar ratio of $r=0.05$, and the instrumental configuration of the EBEX balloon payload, the estimated CMB $B$-mode power spectrum is recovered without bias when the frequency band measurement has 5% uncertainty or less, and the polarization angle calibration has an uncertainty of up to 4$^{\circ}$.
We study the dynamics of radiation pressure supported tori around Schwarzschild black holes, focusing on their oscillatory response to an external perturbation. Using KORAL, a general relativistic radiation hydrodynamics code capable of modeling all radiative regimes from the optically thick to the optically thin, we monitor a sample of models at different initial temperatures and opacities, evolving them in two spatial dimensions for $\sim 165$ orbital periods. The dynamics of models with high opacity is very similar to that of purely hydrodynamics models, and it is characterized by regular oscillations which are visible also in the light curves. As the opacity is decreased, the tori quickly and violently migrate towards the gas-pressure dominated regime, collapsing towards the equatorial plane. When the spectra of the $L_2$ norm of the mass density are considered, high frequency inertial-acoustic modes of oscillations are detected (with the fundamental mode at a frequency $68 M_{\rm BH}^{-1}\,\rm Hz$), in close analogy to the phenomenology of purely hydrodynamic models. An additional mode of oscillation, at a frequency $129 M_{\rm BH}^{-1}\,\rm Hz$, is also found, which can be unambiguously attributed to the radiation. The spectra extracted from the light curves are typically more noisy, indicating that in a real observation such modes would not be easily detected.
Improvements in current instruments and the advent of next-generation instruments will soon push observational 21 cm cosmology into a new era, with high significance measurements of both the power spectrum and the mean ("global") signal of the 21 cm brightness temperature. In this paper we use the recently commenced Hydrogen Epoch of Reionization Array as a worked example to provide forecasts on astrophysical and cosmological parameter constraints. In doing so we improve upon previous forecasts in a number of ways. First, we provide updated forecasts using the latest best-fit cosmological parameters from the Planck satellite, exploring the impact of different Planck datasets on 21 cm experiments. We also show that despite the exquisite constraints that other probes have placed on cosmological parameters, the remaining uncertainties are still large enough to have a non-negligible impact on upcoming 21 cm data analyses. While this complicates high-precision constraints on reionization models, it provides an avenue for 21 cm reionization measurements to constrain cosmology. We additionally forecast HERA's ability to measure the ionization history using a combination of power spectrum measurements and semi-analytic simulations. Finally, we consider ways in which 21 cm global signal and power spectrum measurements can be combined, and propose a method by which power spectrum results can be used to train a compact parameterization of the global signal. This parameterization reduces the number of parameters needed to describe the global signal, increasing the likelihood of a high significance measurement.
With high resolution (0"25 x 0"18) ALMA CO 3-2 observations of the nearby
(D=21 Mpc), extremely radio quiet galaxy NGC1377, we have discovered a high
velocity, very collimated molecular jet with a projected length of $\pm$160 pc.
Along the jet axis we find strong velocity reversals swinging from -180 to +180
km/s. A simple model of a precessing molecular jet can reproduce the
observations. The launch region is inside a radius r<10 pc and the velocity of
the outflowing gas lies between 250 and 600 km/s. The CO emission is clumpy and
the jet molecular mass ranges between 2e6 Msun (light jet) and 2e7 Msun
(massive jet).
We suggest that the driving mechanism of the molecular jet is either a
(fading) radio jet or an accretion disk-wind similar to those found towards
protostars. It seems unlikely that a massive jet could have been driven out by
the current level of nuclear activity which should then have undergone rapid
quenching. In contrast, a light jet would have expelled only 10% of the nuclear
gas and may facilitate nuclear activity instead of suppressing it. The
precession can be powered by a binary supermassive black hole (SMBH) or by gas
of misaligned angular momentum flowing onto a warped accretion disk. Large
columns of H2 in the nucleus of NGC1377 suggest a high rate of recent gas
infall. The current IR emission of NGC1377 may be powered by a SMBH accreting
at a rate of about 10% Eddington. There is tentative evidence that the
molecular gas in the jet is decelerating and that the gas in the outflow
therefore can return and fuel future nuclear growth. Further studies are
required to determine the age and mass of the molecular jet and the role it
plays in the nuclear growth of NGC1377. There is also a broad, cone-like
structure of CO emission in NGC1377 which seems to be a slower, wide-angle
molecular outflow with an estimated molecular mass of approximately 1e8 Msun.
The coupling between spin and torsion in the Einstein-Cartan-Sciama-Kibble theory of gravity generates gravitational repulsion at very high densities, which prevents a singularity in a black hole and may create there a new universe. We show that quantum particle production in such a universe near the last bounce, which represents the Big Bang gives the dynamics that solves the horizon, flatness, and homogeneity problems in cosmology. For a particular range of the particle production coefficient, we obtain a nearly constant Hubble parameter that gives an exponential expansion of the universe with more than 60 $e$-folds, which lasts about $\sim 10^{-42}$ s. This scenario can thus explain cosmic inflation without requiring a fundamental scalar field and reheating. From the obtained time dependence of the scale factor, we follow the prescription of Ellis and Madsen to reconstruct in a non-parametric way a scalar field potential which gives the same dynamics of the early universe. This potential gives the slow-roll parameters of cosmic inflation, from which we calculate the tensor-to-scalar ratio, the scalar spectral index of density perturbations, and its running as functions of the production coefficient. We find that these quantities do not significantly depend on the scale factor at the Big Bounce. Our predictions for these quantities are consistent with the Planck 2015 observations.
In this paper we address the cosmic frequency of technological species. Recent advances in exoplanet studies provide strong constraints on all astrophysical terms in the Drake Equation. Using these and modifying the form and intent of the Drake equation we show that we can set a firm lower bound on the probability that one or more additional technological species have evolved anywhere and at any time in the history of the observable Universe. We find that as long as the probability that a habitable zone planet develops a technological species is larger than ~$10^{-24}$, then humanity is not the only time technological intelligence has evolved. This constraint has important scientific and philosophical consequences.
We present the discovery of HAT-P-57b, a P = 2.4653 day transiting planet around a V = 10.465 +- 0.029 mag, Teff = 7500 +- 250 K main sequence A8V star with a projected rotation velocity of v sin i = 102.1 +- 1.3 km s^-1. We measure the radius of the planet to be R = 1.413 +- 0.054 R_J and, based on RV observations, place a 95% confidence upper limit on its mass of M < 1.85 M_J . Based on theoretical stellar evolution models, the host star has a mass and radius of 1.47 +- 0.12 M_sun, and 1.500 +- 0.050 R_sun, respectively. Spectroscopic observations made with Keck-I/HIRES during a partial transit event show the Doppler shadow of HAT-P-57b moving across the average spectral line profile of HAT-P- 57, confirming the object as a planetary system. We use these observations, together with analytic formulae that we derive for the line profile distortions, to determine the projected angle between the spin axis of HAT-P-57 and the orbital axis of HAT-P-57b. The data permit two possible solutions, with -16.7 deg < lambda < 3.3 deg or 27.6 deg < lambda < 57.4 deg at 95% confidence, and with relative probabilities for the two modes of 26% and 74%, respectively. Adaptive optics imaging with MMT/Clio2 reveals an object located 2.7" from HAT-P-57 consisting of two point sources separated in turn from each other by 0.22". The H and L -band magnitudes of the companion stars are consistent with their being physically associated with HAT-P-57, in which case they are stars of mass 0.61 +- 0.10 M_sun and 0.53 +- 0.08 M_sun. HAT-P-57 is the most rapidly rotating star, and only the fourth main sequence A star, known to host a transiting planet.
We investigate the impact of modified theories of gravity on the kinetic Sunyaev-Zeldovich (kSZ) effect of the cosmic microwave background. We focus on a specific class of $f(R)$ models of gravity and compare their predictions for the kSZ power spectrum to that of the $\Lambda$CDM model. We use a publicly available modified version of Halofit to properly include the nonlinear matter power spectrum of $f(R)$ in the modeling of the kSZ signal. We find that the well known modifications of the growth rate of structure in $f(R)$ can indeed induce sizable changes in the kSZ signal, which are more significant than the changes induced by modifications of the expansion history. We discuss prospects of using the kSZ signal as a complementary probe of modified gravity, giving an overview of assumptions and possible caveats in the modeling.
We study energy flows in geometrically thick accretion discs, both optically thick and thin, using general relativistic, three-dimensional simulations of black hole accretion flows. We find that for non-rotating black holes the efficiency of the total feedback from thick accretion discs is $3\%$ - roughly half of the thin disc efficiency. This amount of energy is ultimately distributed between outflow and radiation, the latter scaling weakly with the accretion rate for super-critical accretion rates, and returned to the interstellar medium. Accretion on to rotating black holes is more efficient because of the additional extraction of rotational energy. However, the jet component is collimated and likely to interact only weakly with the environment, whereas the outflow and radiation components cover a wide solid angle.
We investigate the backreaction of the Affleck-Dine leptogenesis to inflaton dynamics in the F-term hybrid and chaotic inflation models in supergravity. We determine the lightest neutrino mass in both models so that the predictions of spectral index, tensor-to-scalar ratio, and baryon abundance are consistent with observations.
Neutrino masses and light (keV-GeV) sterile neutrinos can arise naturally via a modified, low energy seesaw mechanism if the right-handed neutrinos are charged under a new symmetry broken by a PeV scale vacuum expectation value, presumably tied to supersymmetry breaking. The additional field content also allows for freeze-in production of sterile neutrino dark matter. This framework can accommodate the recently observed 3.5 keV X-ray line, while a straightforward extension of the framework, using the new symmetry and the PeV energy scale, can explain the PeV energy neutrino events at IceCube. Together, these can therefore be taken as hints of the existence of a PeV scale supersymmetric neutrino sector.
We study the preheating phase for multifield models of inflation involving nonminimal couplings. The strong single-field attractor behavior during inflation in these models generically persists after the end of inflation, thereby avoiding the "de-phasing" that is typical in multifield models with minimally coupled scalar fields. Hence we find efficient transfer of energy from the oscillating inflation field(s) to coupled fluctuations. We develop a doubly-covariant formalism for studying such resonances and identify several features of preheating specific to the nonminimal couplings, including effects that arise from the nontrivial field-space manifold. In particular, whereas long-wavelength fluctuations in both the adiabatic and isocurvature directions may be resonantly amplified for small or modest values of the dimensionless couplings, $\xi_I \leq 1$, we find suppression of the growth of long-wavelength isocurvature modes in the limit of strong coupling, $\xi_I \gg 1$.
The description of physical processes in accelerated frames opens a window to numerous new phenomena. One can encounter these effects both in the subatomic world and on a macroscale. In the present work we review our recent results on the study of the electroweak interaction of particles with an accelerated background matter. In our analysis we choose the noninertial comoving frame, where matter is at rest. Our study is based on the solution of the Dirac equation, which exactly takes into account both the interaction with matter and the nonintertial effects. First, we study the interaction of ultrarelativistic neutrinos, electrons and quarks with the rotating matter. We consider the influence of the matter rotation on the resonance in neutrino oscillations and the generation of anomalous electric current of charged particles along the rotation axis. Then, we study the creation of neutrino-antineutrino pairs in a linearly accelerated matter. The applications of the obtained results for elementary particle physics and astrophysics are discussed.
The laser-tracked geodetic satellites LAGEOS, LAGEOS II and LARES are currently employed, among other things, to measure the general relativistic Lense-Thirring effect in the gravitomagnetic field of the spinning Earth with the hope of providing a more accurate test of such a prediction of the Einstein's theory of gravitation than the existing ones. The secular decay $\dot a$ of the semimajor axes $a$ of such spacecrafts, recently measured in an independent way to a $\sigma_{\dot a}\approx 0.1-0.01$ m yr$^{-1}$ accuracy level, may indirectly impact the proposed relativistic experiment through its connection with the classical orbital precessions induced by the Earth's oblateness $J_2$. \textcolor{black}{Indeed,} the systematic bias due to the current measurement errors $\sigma_{\dot a}$ is of the same order of magnitude of, or even larger than, the expected relativistic signal itself; moreover, it grows linearly with the time span $T$ of the analysis. \textcolor{black}{Therefore, the parameter-fitting algorithms must be properly updated in order to suitably cope with such a new source of systematic uncertainty. Otherwise,} an improvement of one-two orders of magnitude in measuring the orbital decay of the satellites of the LAGEOS family would be required to reduce this source of systematic uncertainty to a percent fraction of the Lense-Thirring signature.
We propose a new type of axion inflation with complex structure moduli in the framework of type IIB superstring theory compactified on Calabi-Yau manifold. The inflaton is identified as the axion for the complex structure moduli whose potential is originating from instantonic corrections appearing through the period vector of mirror Calabi-Yau manifold. The axionic shift symmetry is broken down to the discrete one by the inclusion of instantonic correction and certain three-from fluxes. Our proposed inflation scenario is compatible with K\"ahler moduli stabilization. We also study a typical reheating temperature in the case of complex structure moduli inflation.
We present here the general expressions for the acceleration of massive test particles along the symmetry axis of the Kerr metric, and then study the main properties of this acceleration in different regions of the spacetime. In particular, we show that there exists a region near the black hole in which the gravitational field is repulsive. We provide possible physical interpretations about the role of this effect in terms of the different conserved parameters. The studies of these geodesics are important not only to understand better the structure of the Kerr spacetime but also to its use as a possible mechanism for the production of extragalactic jets. Our results are obtained with the help of expressing the geodesics of the Kerr spacetime in terms of the Weyl coordinates.
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Accretion disks around supermassive black holes (SMBHs) in active galactic nuclei contain stars, stellar mass black holes, and other stellar remnants, which perturb the disk gas gravitationally. The resulting density perturbations in turn exert torques on the embedded masses causing them to migrate through the disk in a manner analogous to the behavior of planets in protoplanetary disks. We determine the strength and direction of these torques using an empirical analytic description dependent on local disk gradients, applied to two different analytic, steady-state disk models of SMBH accretion disks. We find that there are radii in such disks where the gas torque changes sign, trapping migrating objects. Our analysis shows that major migration traps generally occur where the disk surface density gradient changes sign from positive to negative, around 20--300$R_{\rm g}$, where $R_{\rm g}=2GM/c^{2}$ is the Schwarzschild radius. At these traps, massive objects in the AGN disk can accumulate, collide, scatter, and accrete. Intermediate mass black hole formation is likely in these disk locations, which may lead to preferential gap and cavity creation at these radii. Our model thus has significant implications for SMBH growth as well as gravitational wave source populations.
We present a study of spatial variations in the metallicity of old red giant branch stars in the Andromeda galaxy. Photometric metallicity estimates are derived by interpolating isochrones for over seven million stars in the Panchromatic Hubble Andromeda Treasury (PHAT) survey. This is the first systematic study of stellar metallicities over the inner 20 kpc of Andromeda's galactic disk. We see a clear metallicity gradient of $-0.020\pm0.004$ dex/kpc from $\sim4-20$ kpc assuming a constant RGB age. This metallicity gradient is derived after correcting for the effects of photometric bias and completeness and dust extinction and is quite insensitive to these effects. The unknown age gradient in M31's disk creates the dominant systematic uncertainty in our derived metallicity gradient. However, spectroscopic analyses of galaxies similar to M31 show that they typically have small age gradients that make this systematic error comparable to the 1$\sigma$ error on our metallicity gradient measurement. In addition to the metallicity gradient, we observe an asymmetric local enhancement in metallicity at radii of 3-6 kpc that appears to be associated with Andromeda's elongated bar. This same region also appears to have an enhanced stellar density and velocity dispersion.
We present the first results from the KMOS AGN Survey at High redshift (KASHz), a VLT/KMOS integral-field spectroscopic survey of z>0.6 AGN. We present galaxy-integrated spectra of 89 X-ray AGN (Lx=10^42-10^45 erg/s), for which we observed [O III] (z=1.1-1.7) or Halpha emission (z=0.6-1.1). The targets have X-ray luminosities representative of the parent AGN population and we explore the emission-line luminosities as a function of X-ray luminosity. For the [O III] targets, ~50 per cent have ionised gas velocities indicative of gas that is dominated by outflows and/or highly turbulent material (i.e., overall line-widths >~600 km/s). The most luminous half (i.e., Lx>6x10^43 erg/s) have a >~2 times higher incidence of such velocities. On the basis of our results, we find no evidence that X-ray obscured AGN are more likely to host extreme kinematics than unobscured AGN. Our KASHz sample has a distribution of gas velocities that is consistent with a luminosity-matched sample of z<0.4 AGN. This implies little evolution in the prevalence of ionised outflows, for a fixed AGN luminosity, despite an order-of-magnitude decrease in average star-formation rates over this redshift range. Furthermore, we compare our Halpha targets to a redshift-matched sample of star-forming galaxies and despite a similar distribution of Halpha luminosities and likely star-formation rates, we find extreme ionised gas velocities are up to ~10x more prevalent in the AGN-host galaxies. Our results reveal a high prevalence of extreme ionised gas velocities in high-luminosity X-ray AGN and imply that the most powerful ionised outflows in high-redshift galaxies are driven by AGN activity.
The Kepler Mission has detected dozens of compact planetary systems with more than four transiting planets. This sample provides a collection of close-packed planetary systems with relatively little spread in the inclination angles of the inferred orbits. A large fraction of the observational sample contains limited multiplicity, begging the question whether there is a true diversity of multi transiting systems, or if some systems merely possess high mutual inclinations, allowing them to appear as single-transiting systems in a transit-based survey. This paper begins an exploration of the effectiveness of dynamical mechanisms in exciting orbital inclination within exoplanetary systems of this class. For these tightly packed systems, we determine that the orbital inclination angles are not spread out appreciably through self-excitation. In contrast, the two Kepler multi-planet systems with additional non-transiting planets are susceptible to oscillations of their inclination angles, which means their currently observed configurations could be due to planet-planet interactions alone. We also provide constraints and predictions for the expected transit duration variations (TDVs) for each planet. In these multi-planet compact Kepler systems, oscillations of their inclination angles are remarkably hard to excite; as a result, they tend to remain continually mutually transiting (CMT-stable). We study this issue further by augmenting the planet masses and determining the enhancement factor required for oscillations to move the systems out of transit. The oscillations of inclination found here inform the recently suggested dichotomy in the sample of solar systems observed by Kepler.
Recent hydrodynamic (HD) simulations have shown that galactic disks evolve to reach well-defined statistical equilibrium states. The star formation rate (SFR) self-regulates until energy injection by star formation feedback balances dissipation and cooling in the interstellar medium (ISM), and provides vertical pressure support to balance gravity. In this paper, we extend our previous models to allow for a range of initial magnetic field strengths and configurations, utilizing three-dimensional, magnetohydrodynamic (MHD) simulations. We show that a quasi-steady equilibrium state is established as rapidly for MHD as for HD models unless the initial magnetic field is very strong or very weak, which requires more time to reach saturation. Remarkably, models with initial magnetic energy varying by two orders of magnitude approach the same asymptotic state. In the fully saturated state of the fiducial model, the integrated energy proportions E_kin:E_th:E_mag,t:E_mag,o are 0.35:0.39:0.15:0.11, while the proportions of midplane support P_turb:P_th:\Pi_mag,t:\Pi_mag,o are 0.49:0.18:0.18:0.15. Vertical profiles of total effective pressure satisfy vertical dynamical equilibrium with the total gas weight at all heights. We measure the "feedback yields" \eta_c=P_c/\Sigma_SFR (in suitable units) for each pressure component, finding that \eta_turb~4 and \eta_th~1 are the same for MHD as in previous HD simulations, and \eta_mag,t~1. These yields can be used to predict the equilibrium SFR for a local region in a galaxy based on its observed gas and stellar surface densities and velocity dispersions. As the ISM weight (or dynamical equilibrium pressure) is fixed, an increase in $\eta$ from turbulent magnetic fields reduces the predicted \Sigma_SFR by ~25% relative to the HD case.
Cosmic reionization by starlight from early galaxies affected their evolution, thereby impacting reionization, itself. Star formation suppression, for example, may explain the observed underabundance of Local Group dwarfs relative to N-body predictions for Cold Dark Matter. Reionization modelling requires simulating volumes large enough ~(100 Mpc)^3 to sample reionization "patchiness", while resolving millions of galaxy sources above ~10^8 Msun, combining gravitational and gas dynamics with radiative transfer. Modelling the Local Group requires initial cosmological density fluctuations pre-selected to form the well-known structures of the local universe today. Cosmic Dawn ("CoDa") is the first such fully-coupled, radiation-hydrodynamics simulation of reionization of the local universe. Our new hybrid CPU-GPU code, RAMSES-CUDATON, performs hundreds of radiative transfer and ionization rate-solver timesteps on the GPUs for each hydro-gravity timestep on the CPUs. CoDa simulated (91 Mpc)^3 with 4096^3 particles and cells, to redshift 4.23, on ORNL supercomputer Titan, utilizing 8192 cores and 8192 GPUs. Global reionization ended slightly later than observed. However, a simple temporal rescaling which brings the evolution of ionized fraction into agreement with observations also reconciles ionizing flux density, cosmic star formation history, CMB electron scattering optical depth and galaxy UV luminosity function with their observed values. Haloes below ~3 x 10^9 Msun were severely affected by the rising UV background: photoionization heating suppressed their star formation. For most of reionization, star formation was dominated by haloes between 10^10 - 10^11Msun. Intergalactic filaments display sheathed structures, with hot envelopes surrounding cooler cores, but do not self-shield, unlike regions denser than 100 rho_average.
We present the CosmoBolognaLib, a large set of Open Source C++ numerical libraries for cosmological calculations. CosmoBolognaLib is a living project aimed at defining a common numerical environment for cosmological investigations of the large-scale structure of the Universe. In particular, one of the primary focuses of this software is to help in handling astronomical catalogues, both real and simulated, measuring one-point, two-point and three-point statistics in configuration space, and performing cosmological analyses. In this paper, we discuss the main features of this software, providing an overview of all the available C++ classes implemented up to now. Both the CosmoBolognaLib and their associated doxygen documentation can be freely downloaded at https://github.com/federicomarulli/CosmoBolognaLib. We provide also some examples to explain how these libraries can be included in either C++ or Python codes.
Radio emission from radio-quiet quasars may be due to star formation in the quasar host galaxy, to a jet launched by the supermassive black hole, or to relativistic particles accelerated in a wide-angle radiatively-driven outflow. In this paper we examine whether radio emission from radio-quiet quasars is a byproduct of star formation in their hosts. To this end we use infrared spectroscopy and photometry from Spitzer and Herschel to estimate or place upper limits on star formation rates in hosts of ~300 obscured and unobscured quasars at z<1. We find that low-ionization forbidden emission lines such as [NeII] and [NeIII] are likely dominated by quasar ionization and do not provide reliable star formation diagnostics in quasar hosts, while PAH emission features may be suppressed due to the destruction of PAH molecules by the quasar radiation field. While the bolometric luminosities of our sources are dominated by the quasars, the 160 micron fluxes are likely dominated by star formation, but they too should be used with caution. We estimate median star formation rates to be 6-29 Msun/year, with obscured quasars at the high end of this range. This star formation rate is insufficient to explain the observed radio emission from quasars by an order of magnitude, with log(L_radio, observed/L_radio, SF)=0.6-1.3 depending on quasar type and star formation estimator. Although radio-quiet quasars in our sample lie close to the 8-1000 micron infrared / radio correlation characteristic of the star-forming galaxies, both their infrared emission and their radio emission are dominated by the quasar activity, not by the host galaxy.
We report on a search for monochromatic $\gamma$-ray features in the spectra of galaxy clusters observed by the \emph{Fermi} Large Area Telescope. Galaxy clusters are the largest structures in the Universe that are bound by dark matter (DM), making them an important testing ground for possible self-interactions or decays of the DM particles. Monochromatic $\gamma$-ray lines provide a unique signature due to the absence of astrophysical backgrounds and are as such considered a smoking-gun signature for new physics. An unbinned joint likelihood analysis of the sixteen most promising clusters using five years of data at energies between 10 and 400 GeV revealed no significant features. For the case of self-annihilation, we set upper limits on the monochromatic velocity-averaged interaction cross section. These limits are compatible with those obtained from observations of the Galactic Center, albeit weaker due to the larger distance to the studied clusters.
We check the performance of the {\sl\,PARSEC} tracks in reproducing the blue loops of intermediate age and young stellar populations at very low metallicity. We compute new evolutionary {\sl\,PARSEC} tracks of intermediate- and high-mass stars from 2\Msun to 350\Msun with enhanced envelope overshooting (EO), EO=2\HP and 4\HP, for very low metallicity, Z=0.0005. The input physics, including the mass-loss rate, has been described in {\sl\,PARSEC}~V1.2 version. By comparing the synthetic color-magnitude diagrams (CMDs) obtained from the different sets of models with envelope overshooting EO=0.7\HP (the standard {\sl\,PARSEC} tracks), 2\HP and 4\HP, with deep observations of the Sagittarius dwarf irregular galaxy (SagDIG), we find an overshooting scale EO=2\HP to best reproduce the observed loops. This result is consistent with that obtained by \citet{Tang_etal14} for Z in the range 0.001-0.004. We also discuss the dependence of the blue loop extension on the adopted instability criterion and find that, contrary to what stated in literature, the Schwarzschild criterion, instead of the Ledoux criterion, favours the development of blue loops. Other factors that could affect the CMD comparisons such as differential internal extinction or the presence of binary systems are found to have negligible effects on the results. We thus confirm that, in presence of core overshooting during the H-burning phase, a large envelope overshooting is needed to reproduce the main features of the central He-burning phase of intermediate- and high-mass stars.
We use three-dimensional magnetohydrodynamic (MHD) simulations to investigate the quasi-equilibrium states of galactic disks regulated by star formation feedback. We incorporate effects from massive-star feedback via time-varying heating rates and supernova (SN) explosions. We find that the disks in our simulations rapidly approach a quasi-steady state that satisfies vertical dynamical equilibrium. The star formation rate (SFR) surface density self-adjusts to provide the total momentum flux (pressure) in the vertical direction that matches the weight of the gas. We quantify feedback efficiency by measuring feedback yields, \eta_c\equiv P_c/\Sigma_SFR (in suitable units), for each pressure component. The turbulent and thermal feedback yields are the same for HD and MHD simulations, \eta_th~1 and \eta_ turb~4, consistent with the theoretical expectations. In MHD simulations, turbulent magnetic fields are rapidly generated by turbulence, and saturate at a level corresponding to \eta_mag,t~1. The presence of magnetic fields enhances the total feedback yield and therefore reduces the SFR, since the same vertical support can be supplied at a smaller SFR. We suggest further numerical calibrations and observational tests in terms of the feedback yields.
Even simple inflationary scenarios have many free parameters. Beyond the variables appearing in the inflationary action, these include dynamical initial conditions, the number of fields, and couplings to other sectors. These quantities are often ignored but cosmological observables can depend on the unknown parameters. We use Bayesian networks to account for a large set of inflationary parameters, deriving generative models for the primordial spectra that are conditioned on a hierarchical set of prior probabilities describing the initial conditions, reheating physics, and other free parameters. We use $N_f$--quadratic inflation as an illustrative example, finding that the number of $e$-folds $N_*$ between horizon exit for the pivot scale and the end of inflation is typically the most important parameter, even when the number of fields, their masses and initial conditions are unknown, along with possible conditional dependencies between these parameters.
We investigate the observational signatures and physical origin of
ram-pressure stripping (RPS) in 63 massive galaxy clusters at $z=0.3-0.7$,
based on images obtained with the Hubble Space Telescope. Using a training set
of a dozen "jellyfish" galaxies identified earlier in the same imaging data, we
define morphological criteria to select 211 additional, less obvious cases of
RPS. Spectroscopic follow-up observations of 124 candidates so far confirmed 53
as cluster members. For the brightest and most favourably aligned systems we
visually derive estimates of the projected direction of motion based on the
orientation of apparent compression shocks and debris trails.
Our findings suggest that the onset of these events occurs primarily at large
distances from the cluster core ($>400$ kpc), and that the trajectories of the
affected galaxies feature high impact parameters. Simple models show that such
trajectories are highly improbable for galaxy infall along filaments but common
for infall at high velocities, even after observational biases are accounted
for, provided the duration of the resulting RPS events is $\lesssim$500 Myr. We
thus tentatively conclude that extreme RPS events are preferentially triggered
by cluster mergers, an interpretation that is supported by the disturbed
dynamical state of many of the host clusters. This hypothesis implies that
extreme RPS might occur also near the cores of merging poor clusters or even
merging groups of galaxies.
Finally, we present nine additional "jellyfish" galaxies at z$>$0.3
discovered by us, thereby doubling the number of such systems known at
intermediate redshift.
The remarkable observation that many single O stars spin very rapidly can be explained if they accreted angular momentum from a mass-transferring companion before that star blew up as a supernova. To test this hypothesis we have measured the spin rates of eight O stars in Wolf-Rayet (WR) + O binaries, increasing the total sample size of such O stars' measured spins from two to ten. The average v sin i for the sample of 10 O stars in these binaries is a strongly super-synchronous rate of 237 km/s, with individual star's values ranging from 129 to 331 km/s. Polarimetric and other determinations of these systems' sin i allow us to determine an average equatorial rotation velocity of 290 km/s for these 10 O stars, with individual star's velocities ranging from 140 to 496 km/s. This is strong observational evidence that Roche lobe overflow mass transfer from a WR progenitor companion has played a critical role in the evolution of WR+OB binaries. While theory predicts that this mass transfer rapidly spins-up the O-type mass gainer to a nearly break-up rotational velocity v ~ 750 km/s, the observed average rotation velocity of the O-type stars in our sample is less than half that large. This demonstrates that, even over the relatively short WR-phase timescale, tidal effects causing rotational spin-down must be very efficient. A challenge to tidal synchronization theory is that the two longest-period binaries in our sample (with periods of 29.7 and 78.5 days) unexpectedly display super-synchronous rotation.
The Alpha Magnetic Spectrometer (AMS-02) is a state of the art particle detector measuring cosmic rays (CRs) on the International Space Station (ISS) since May 19th 2011. AMS-02 identifies CR leptons and nuclei in the energy range from hundreds MeV to few TeV per nucleon. Several sub-detector systems allow for redundant particle identification with unprecedented precision, a powerful lepton-hadron separation, and a high purity of the antimatter signal. The new AMS-02 leptonic data from 1 to 500 GeV are presented and discussed. These new data indicate that new sources of CR leptons need to be included to describe the observed spectra at high energies. Explanations of this anomaly may be found either in dark-matter particles annihilation or in the existence of nearby astrophysical sources of $e^{\pm}$. Future data at higher energies and forthcoming measurements on the antiproton spectrum and the boron-to-carbon ratio will be crucial in providing the discrimination among the different scenario.
We examine the internal consistency of the Planck 2015 cosmic microwave background (CMB) temperature anisotropy power spectrum. We show that tension exists between cosmological constant cold dark matter (LCDM) model parameters inferred from multipoles l<1000 (roughly those accessible to WMAP), and from l>=1000, particularly the CDM density, Omega_ch^2, which is discrepant at 2.5 sigma for a Planck-motivated prior on the optical depth, tau=0.07+/-0.02. We find some parameter tensions to be larger than previously reported because of inaccuracy in the code used by the Planck Collaboration to generate model spectra. The Planck l>=1000 constraints are also in tension with low-redshift data sets, including Planck's own measurement of the CMB lensing power spectrum (2.4 sigma), and the most precise baryon acoustic oscillation (BAO) scale determination (2.5 sigma). The Hubble constant predicted by Planck from l>=1000, H_0=64.1+/-1.7 km/s/Mpc, disagrees with the most precise local distance ladder measurement of 73.0+/-2.4 km/s/Mpc at the 3.0 sigma level, while the Planck value from l<1000, 69.7+/-1.7 km/s/Mpc, is consistent within 1 sigma. A discrepancy between the Planck and South Pole Telescope (SPT) high-multipole CMB spectra disfavors interpreting these tensions as evidence for new physics. We conclude that the parameters from the Planck high-multipole spectrum probably differ from the underlying values due to either an unlikely statistical fluctuation or unaccounted-for systematics persisting in the Planck data.
The first observational evidence for the violation of the maximum turn-around radius on the galaxy group scale is presented. The NGC 5353/4 group is chosen as an ideal target of our investigation of the bound-violation because of its proximity, low-density environment, optimal mass scale, and existence of a nearby thin straight filament. Using the observational data on the line-of-sight velocities and three dimensional distances of the filament galaxies located in the bound zone of the NGC 5353/4 group, we construct their radial velocity profile as a function of separation distance from the group center and then compares it with the analytic formula obtained empirically by Falco et al. (2014) to find the best-fit value of an adjustable parameter with the help of the maximum likelihood method. The turn-around radius of NGC 5353/4 is determined as the separation distance where the adjusted analytic formula for the radial velocity profile yields zero. The estimated turn-around radius of NGC 5353/4 turns out to substantially exceed the upper limit predicted by the spherical model based on the LambdaCDM cosmology. Even when the restrictive condition of spherical symmetry is released, the estimated value is found to be only marginally consistent with the LambdaCDM expectation.
We present the first evidence of clear signatures of tidal distortions in the density distribution of the fascinating open cluster NGC~6791. We find that the 2D density map shows a clear elongation and an irregular distribution starting from $\sim 300^{\prime\prime}$ from the cluster center and two tails extending in opposite directions beyond the tidal radius. These features are aligned to both the absolute proper motion and to the Galactic centre directions. Accordingly we find that both the surface brightness and star count density profiles reveal a departure from a King model starting from $\sim600^{\prime\prime}$. These observational evidences suggest that NGC~6791 is currently undergoing mass-loss likely due to gravitational shocking and interactions with the tidal field of the Milky Way. We derive the expected mass-loss due to stellar evolution and tidal interactions and we estimate the initial cluster mass to be $M_{ini} = (1.5-4.0 ) \times 10^5 M_{\odot}$.
Shadows of black holes surrounded by an optically thin emitting medium have been extensively discussed in the literature. The Hioki-Maeda algorithm is a simple recipe to characterize the shape of these shadows and determine the parameters of the system. Here we extend their idea to the case of a dressed black hole, namely a black hole surrounded by a geometrically thin and optically thick accretion disk. While the boundary of the shadow of black holes surrounded by an optically thin emitting medium corresponds to the apparent photon capture sphere, that of dressed black holes corresponds to the apparent image of the innermost stable circular orbit. Even in this case, we can characterize the shape of the shadow and infer the black hole spin and viewing angle. The shape and the size of the shadow of a dressed black hole are strongly affected by the black hole spin and inclination angle. Despite that, it seems that we cannot extract any additional information from it. Here we study the possibility of testing the Kerr metric. Even with the full knowledge of the boundary of the shadow, those of Kerr and non-Kerr black holes are very similar and it is eventually very difficult to distinguish the two cases.
In external Compton scenario, we investigate the formation of the very hard electron spectrum in the fast-cooling regime, using a time-dependent emission model. It is shown that a very hard electron distribution $N'_{\rm e}(\gp)\propto\gp^{-p}$ with the spectral index $p\sim1.3$ is formed below the minimum energy of injection electron when inverse Compton scattering takes place in the Klein-Nishina regime, i.e., inverse Compton scattering of relativistic electrons on broad-line region radiation in flat spectrum radio quasars. This produces a very hard gamma-ray spectrum, and can reasonably explain the very hard \emph{Fermi}-LAT spectrum of the flat spectrum radio quasar 3C 279 during the extreme gamma-ray flare in 2013 December. We examine the impact of gamma-ray emission site on the evolution of electron distribution and their radiative output in detail. We find that such hard \emph{Fermi}-LAT spectrum and simultaneous X-ray observations can put a stringent constraint on the gamma-ray emission site. Variability features in this scenario are simply discussed.
Many giant exoplanets in close orbits have observed radii which exceed theoretical predictions. One suggested explanation for this discrepancy is heat deposited deep inside the atmospheres of these "hot Jupiters". Here, we study extended power sources which distribute heat from the photosphere to the deep interior of the planet. Our analytical treatment is a generalization of a previous analysis of localized "point sources". We model the deposition profile as a power law in the optical depth and find that planetary cooling and contraction halt when the internal luminosity (i.e. cooling rate) of the planet drops below the heat deposited in the planet's convective region. A slowdown in the evolutionary cooling prior to equilibrium is possible only for sources which do not extend to the planet's center. We estimate the Ohmic dissipation resulting from the interaction between the atmospheric winds and the planet's magnetic field, and apply our analytical model to Ohmically heated planets. Our model can account for the observed radii of many inflated planets which have equilibrium temperatures $\approx 1500\textrm{ K}-2500\textrm{ K}$, and are inflated to a radius $\approx 1.5 R_J$. However, some extremely inflated planets remain unexplained by our model. We also argue that Ohmically inflated planets have already reached their equilibrium phase, and no longer contract. Following Wu & Lithwick (2013) who argued that Ohmic heating could only suspend and not reverse contraction, we calculate the time it takes Ohmic heating to re-inflate a cold planet to its equilibrium configuration. We find that while it is possible to re-inflate a cold planet, the re-inflation timescales are longer by a factor of $\approx 30$ than the cooling time.
We investigate the production of the hypermagnetic gyrotropy when the electric and magnetic gauge couplings evolve at different rates, as it happens in the the relativistic theory of the Van der Waals forces. If a pseudo-scalar interaction breaks the duality symmetry of the corresponding equations, the gyrotropic configurations of the hypermagnetic fields can be amplified from the vacuum during an inflationary stage of expansion. After charting the parameter space of the model in terms of the rates of evolution of the magnetic and electric gauge couplings, we identify the regions where the gyrotropy is sufficiently intense to seed the baryon asymmetry of the Universe at the electroweak epoch while the backreaction constraints, the strong coupling bounds and the other astrophysical limits are concurrently satisfied.
WEAVE is a 1000-fiber multi-object spectroscopic facility for the 4.2~m William Herschel Telescope. It will feature a double-headed pick-and-place fiber positioning robot comprising commercially available robotic axes. This paper presents results on the performance of these axes, obtained by testing a prototype system in the laboratory. Positioning accuracy is found to be better than the manufacturer's published values for the tested cases, indicating that the requirement for a maximum positioning error of 8.0~microns is achievable. Field reconfiguration times well within the planned 60 minute observation window are shown to be likely when individual axis movements are combined in an efficient way.
Compact stars consisting of massless quark matter and fermionic dark matter are studied by solving the Tolman-Oppenheimer-Volkoff equations for two fluids separately. Dark matter is further investigated by incorporating inter-fermionic interactions among the dark matter particles. The properties of stars made of quark matter particles and self-interacting and free dark matter particles are explored by obtaining their mass-radius relations. The regions of stability for such a compact star are determined and it is demonstrated that the maximum stable total mass of such a star decreases approximately linearly with increasing dark matter fraction.
The observational effects of the 'Infrared Catastrophe' are discussed in view of the very late observations of the Type Ia SN 2011fe. Our model spectra at 1000d take non-local radiative transfer into account, and find that this has a crucial impact on the spectral formation. Although rapid cooling of the ejecta to a few 100 K occurs also in these models, the late-time optical/NIR flux is brighter by 1-2 magnitudes due to redistribution of UV emissivity, resulting from non-thermal excitation and ionization. This effect brings models into better agreement with late-time observations of SN 2011fe and other Type Ia supernovae, and offers a solution to the long standing discrepancy between models and observations. The models show that spectral formation shifts from Fe II and Fe III at 300d to Fe I at 1000d, which explains the apparent wavelength shifts seen in SN2011fe. We discuss effects of time dependence and energy input from 57Co, finding both to be important at 1000d.
Recently, the IC/CMB X-ray mechanism has been strongly disfavoured for 3C 273 and PKS 0637-752 since the anomalously hard and steady gamma-ray emission predicted by such models violates the observational results from Fermi-LAT. Here we propose the proton synchrotron origin of the X ray-gamma ray flux from the knots of PKS 0637-752 with a reasonable budget in luminosity, by considering synchrotron radiation from an accelerated proton population. Moreover, for the source 3C 273, some of the optical data points could not be explained by electron synchrotron (Meyer et al. 2015), which we have included in our updated proton synchrotron model. We also show that TeV emission from large scale quasar jets in principle, can arise from proton synchrotron, which we discuss in the context of knot wk8.9 of PKS 0637-752.
This is the first in a series of papers presenting methods and results from the Young Solar Analogs Project, which began in 2007. This project monitors both spectroscopically and photometrically a set of 31 young (300 - 1500 Myr) solar-type stars with the goal of gaining insight into the space environment of the Earth during the period when life first appeared. From our spectroscopic observations we derive the Mount Wilson $S$ chromospheric activity index ($S_{\rm MW}$), and describe the method we use to transform our instrumental indices to $S_{\rm MW}$ without the need for a color term. We introduce three photospheric indices based on strong absorption features in the blue-violet spectrum -- the G-band, the Ca I resonance line, and the Hydrogen-$\gamma$ line -- with the expectation that these indices might prove to be useful in detecting variations in the surface temperatures of active solar-type stars. We also describe our photometric program, and in particular our "Superstar technique" for differential photometry which, instead of relying on a handful of comparison stars, uses the photon flux in the entire star field in the CCD image to derive the program star magnitude. We present time series plots of our spectroscopic data for all four indices, and carry out extensive statistical tests on those time series demonstrating the reality of variations on timescales of years in all four indices. We also statistically test for and discover correlations and anti-correlations between the four indices. We discuss the physical basis of those correlations. As it turns out, the "photospheric" indices appear to be most strongly affected by continuum emission. We thus anticipate that these indices may prove to be useful proxies for monitoring continuum emission in the near ultraviolet.
The thermodynamical evolution of gas during the collapse of the primordial star-forming cloud depends significantly on the initial degree of rotation. However, there is no clear understanding of how the initial rotation can affect the heating and cooling process and hence the temperature that leads to the fragmentation of the gas during Population III star formation. We report the results from three\hbox{-}dimensional, smoothed-particle hydrodynamics (SPH) simulations of a rotating self-gravitating primordial gas cloud with a modified version of the Gadget-2 code, in which the initial ratio of the rotational to the gravitational energy ($\beta_0$) is varied over two orders of magnitude. We find that despite the lack of any initial turbulence and magnetic fields in the clouds, the angular momentum distribution leads to the formation and build-up of a disk that fragments into several clumps. We further examine the behavior of the protostars that form in both idealized as well as more realistic minihalos from the cosmological simulations. The thermodynamical evolution and the fragmentation behavior of the cosmological minihalos are similar to that of the artificial cases, especially in those with a similar $\beta_0$-parameter. Protostars with a higher rotation support exhibit spiral-arm-like structures on several scales, and have lower accretion rates. These type of clouds tend to fragment more, while some of the protostars escape from the cluster with the possibility of surviving until the present day. They also take much longer to form compared to their slowly rotating counterparts. We conclude that the use of appropriate initial conditions of the gas in minihalos is a pivotal and decisive quantity to study the evolution and final fate of the primordial stars.
Most massive galaxies are thought to contain a supermassive black holes in their centre surrounded by a tenuous gas environment, leading to no significant emission. In these quiescent galaxies, tidal disruption events represent a powerful detection method for the central black hole. Following the disruption, the stellar debris evolve into an elongated gas stream, which partly falls back towards the disruption site and accrete onto the black hole producing a luminous flare. Using an analytical treatment, we investigate the interaction between the debris stream and the gas environment of quiescent galaxies. Although we find dynamical effects to be negligible, we demonstrate that Kelvin-Helmholtz instability can lead to the dissolution of the stream into the ambient medium before it reaches the black hole, likely dimming the associated flare. Furthermore, we find this effect to be enhanced for disruptions involving more massive black holes and/or giant stars. Consequently, although disruptions of evolved stars have been proposed as a useful probe of black holes with masses $\gtrsim 10^8 \, {\rm M}_\odot$, we argue that the associated flares are likely less luminous than expected.
Protoplanetary disks fragment due to gravitational instability when there is enough mass for self-gravitation, described by the Toomre parameter, and when heat can be lost at a rate comparable to the local dynamical timescale, described by t_c=beta Omega^-1. Simulations of self-gravitating disks show that the cooling parameter has a rough critical value at beta_crit=3. When below beta_crit, gas overdensities will contract under their own gravity and fragment into bound objects while otherwise maintaining a steady state of gravitoturbulence. However, previous studies of the critical cooling parameter have found dependence on simulation resolution, indicating that the simulation of self-gravitating protoplanetary disks is not so straightforward. In particular, the simplicity of the cooling timescale t_c prevents fragments from being disrupted by pressure support as temperatures rise. We alter the cooling law so that the cooling timescale is dependent on local surface density fluctuations, a means of incorporating optical depth effects into the local cooling of an object. For lower resolution simulations, this results in a lower critical cooling parameter and a disk more stable to gravitational stresses suggesting the formation of large gas giants planets in large, cool disks is generally suppressed by more realistic cooling. At our highest resolution however, the model becomes unstable to fragmentation for cooling timescales up to beta = 10.
Supernova remnants (SNRs) have long been considered the leading candidates for the accelerators of cosmic rays within the Galaxy through the process of diffusive shock acceleration. The connection between SNRs and cosmic rays is supported by the detection of high energy (HE; 100 MeV to 100 GeV) and very high energy (VHE; 100 GeV to 100 TeV) gamma rays from young and middle-aged SNRs. However, the interpretation of the gamma-ray observations is not unique. This is because gamma rays can be produced both by electrons through non-thermal Bremsstrahlung and inverse Compton scattering, and by protons through proton-proton collisions and subsequent neutral-pion decay. To disentangle and quantify the contributions of electrons and protons to the gamma-ray flux, it is necessary to measure precisely the spectra and morphology of SNRs over a broad range of gamma-ray energies. Cassiopeia A (Cas A) is one such young SNR (~ 350 years) which is bright in radio and X-rays. It has been detected as a bright point source in HE gamma rays by Fermi-LAT and in VHE gamma rays by HEGRA, MAGIC and VERITAS. Cas A has been observed with VERITAS for more than 60 hours, tripling the published exposure. The observations span 2007-2013, and half of the data were taken at large zenith angles to boost the effective area above few TeV. We will present the detailed spectral and morphological results from the complete dataset.
Multiple stellar populations in the Milky Way globular clusters manifest themselves with a large variety. Although chemical abundance variations in light elements, including He, are ubiquitous, the amount of these variations is different in different globulars. Stellar populations with distinct Fe, C+N+O and slow-neutron capture elements have been now detected in some globular clusters, whose number will likely increase. All these chemical features correspond to specific photometric patterns. I review the chemical+photometric features of the multiple stellar populations in globular clusters and discuss how the interpretation of data is being more and more challenging. Very excitingly, the origin and evolution of globular clusters is being a complex puzzle to compose.
Substantial evidence points to dusty, geometrically thick tori obscuring the central engines of active galactic nuclei, but so far no mechanism satisfactorily explains why cool dust in the torus remains in a puffy geometry. Infrared (IR) radiation pressure on dust can play a significant role in shaping the torus, yet the separation of hydrodynamic evolution from radiative transfer (RT) in previous work on radiation-supported tori precluded a self-consistent picture. Here we present radiative hydrodynamics simulations of an initially smooth torus; we solve the hydrodynamics equations, the time-dependent multi-angle group IR RT equation, and the time-independent ultraviolet (UV) RT equation. IR radiation is highly anisotropic, leaving primarily through the central hole of the torus. The inner edge of the torus exhibits a break in axisymmetry under the influence of radiation and differential rotation. In addition, UV radiation pressure on dust launches a strong wind along the inner edge of the torus with speed $\sim 5.3\times10^3 (M/10^7 M_\odot)^{1/4} [L_\mathrm{UV}/(0.1 L_\mathrm E)]^{1/4} \mathrm{km}\,\mathrm s^{-1}$ and mass loss rate $\sim 0.12 (M/10^7 M_\odot)^{3/4} [L_\mathrm{UV}/(0.1 L_\mathrm E)]^{3/4} M_\odot\,\mathrm{yr}^{-1}$, where $M$, $L_\mathrm{UV}$, and $L_\mathrm E$ are the mass, UV luminosity, and Eddington luminosity of the central object respectively; these values are comparable to those inferred from observations.
We consider a model for the low-luminosity gamma-ray burst GRB 060218 that plausibly accounts for multiwavelength observations to day 20. The model components are: (1) a long-lived ($t_j \sim 3000$ s) central engine and accompanying low-luminosity ($L_j \sim 10^{47}$ erg s$^{-1}$), semirelativistic ($\gamma \sim 10$) jet; (2) a low-mass ($ \sim 10^{-2} M_\odot$) envelope surrounding the progenitor star; and (3) a modest amount of dust ($A_V \sim 0.1$ mag) in the interstellar environment. Blackbody emission from the transparency radius in a low-power jet outflow can fit the prompt thermal X-ray emission, and the nonthermal X-rays and gamma-rays may be produced via Compton scattering of thermal photons from hot leptons in the jet interior or the external shocks. The later mildly relativistic phase of this outflow can produce the radio emission via synchrotron radiation from the forward shock. Meanwhile, interaction of the associated SN 2006aj with a circumstellar envelope extending to $\sim10^{13}$ cm can explain the early optical emission. The X-ray afterglow can be interpreted as a light echo of the prompt emission from dust at $\sim 30$ pc. Our model is a plausible alternative to that of Nakar, who recently proposed shock breakout of a jet smothered by an extended envelope as the source of prompt emission. Both our results and Nakar's suggest that bursts such as GRB 060218 may originate from unusual progenitors with extended circumstellar envelopes, and that a jet is necessary to decouple the prompt emission from the supernova.
There is much observational evidence that active star formation is taking place in the HII regions Sh 2-255 -- 257. We present a photometric study of this star forming region (SFR) using imaging data obtained in passbands from the optical to the mid-infrared in order to study the star formation process. A total of 218 members were identified using various selection criteria based on their observational properties. The SFR is reddened by at least E(B-V) = 0.8 mag, and the reddening law toward the region is normal (R_V = 3.1). From the zero-age main sequence fitting method it is confirmed that the SFR is 2.1 +/- 0.3 kpc from the Sun. The median age of the identified members is estimated to be about 1.3 Myr from comparison of the Hertzsprung-Russell diagram (HRD) with stellar evolutionary models. The initial mass function (IMF) is derived from the HRD and the near-infrared (J, J-H) color-magnitude diagram. The slope of the IMF is about Gamma = -1.6 +/- 0.1, which is slightly steeper than that of the Salpeter/Kroupa IMF. It implies that low-mass star formation is dominant in the SFR. The sum of the masses of all the identified members provides the lower limit of the cluster mass (169M_sun). We also analyzed the spectral energy distribution (SED) of pre-main sequence stars using the SED fitting tool of Robitaille et al. and confirm that there is a significant discrepancy between stellar mass and age obtained from two different methods based on the SED fitting tool and the HRD.
Global characteristics of the small-scale gravity wave (GW) field in the Martian atmosphere obtained from a high-resolution general circulation model (GCM) are presented for the first time. The simulated GW-induced temperature variances are in a good agreement with available radio occultation data in the lower atmosphere between 10 and 30 km. The model reveals a latitudinal asymmetry with stronger wave generation in the winter hemisphere, and two distinctive sources of GWs: mountainous regions and the meandering winter polar jet. Orographic GWs are filtered while propagating upward, and the mesosphere is primarily dominated by harmonics with faster horizontal phase velocities. Wave fluxes are directed mainly against the local wind. GW dissipation in the upper mesosphere generates body forces of tens of m~s$^{-1}$~sol$^{-1}$, which tend to close the simulated jets. The results represent a realistic surrogate for missing observations, which can be used for constraining GW parameterizations and validating GCM simulations.
Water probes the dynamics in young stellar objects (YSOs) effectively, especially shocks in molecular outflows. It is a key molecule for exploring whether the physical properties of low-mass protostars can be extrapolated to massive YSOs. As part of the WISH key programme, we investigate the dynamics and the excitation conditions of shocks along the outflow cavity wall as function of source luminosity. Velocity-resolved Herschel-HIFI spectra of the H2O 988, 752, 1097 GHz and 12CO J=10-9, 16-15 lines were analysed for 52 YSOs with bolometric luminosities (L_bol) ranging from <1 to >10^5 L_sun. The profiles of the H2O lines are similar, indicating that they probe the same gas. We see two main Gaussian emission components in all YSOs: a broad component associated with non-dissociative shocks in the outflow cavity wall (cavity shocks) and a narrow component associated with quiescent envelope material. More than 60% of the total integrated intensity of the H2O lines (L_H2O) comes from the cavity shock component. The H2O line widths are similar for all YSOs, whereas those of 12CO 10-9 increase slightly with L_bol. The excitation analysis of the cavity shock component, performed with the non-LTE radiative transfer code RADEX, shows stronger 752 GHz emission for high-mass YSOs, likely due to pumping by an infrared radiation field. As previously found for CO, a strong correlation with slope unity is measured between log(L_H2O) and log(L_bol), which can be extrapolated to extragalactic sources. We conclude that the broad component of H2O and high-J CO lines originate in shocks in the outflow cavity walls for all YSOs, whereas lower-J CO transitions mostly trace entrained outflow gas. The higher UV field and turbulent motions in high-mass objects compared to their low-mass counterparts may explain the slightly different kinematical properties of 12CO 10-9 and H2O lines from low- to high-mass YSOs.
The conventional $\Lambda$CDM cosmological model supplemented by the inflation concept describes the Universe very well. However, there are still a few concerns: new Planck data impose constraints on the shape of the inflaton potential, which exclude a lot of inflationary models; dark matter is not detected directly, and dark energy is not understood theoretically on a satisfactory level. In this brief sketch we investigate an alternative cosmological model with spherical spatial geometry and an additional perfect fluid with the constant parameter $\omega=-1/3$ in the linear equation of state. It is demonstrated explicitly that in the framework of such a model it is possible to satisfy the supernovae data at the same level of accuracy as within the $\Lambda$CDM model and at the same time suppose that the observed cosmic microwave background (CMB) radiation originates from a very limited space region. This is ensured by introducing an additional condition of light propagation between the antipodal points during the age of the Universe. Consequently, the CMB uniformity can be explained without the inflation scenario. The corresponding drawbacks of the model with respect to its comparison with the CMB data are also discussed.
We calculate the correlation function of 79,091 galaxy clusters in the redshift region of $0.05 \leq z \leq 0.5$ selected from the WH15 cluster catalog. With a weight of cluster mass, a significant baryon acoustic oscillation (BAO) peak is detected on the correlation function with a significance of $3.9 \sigma$. By fitting the correlation function with a $\Lambda$CDM model curve, we find $D_v(z = 0.331) r_d^{fid}/r_d = 1269.4 \pm 58$ Mpc which is consistent with the Planck 2015 cosmology. We find that the correlation functions of the higher mass sub-samples show a higher amplitude at small scales of $r < 80~h^{-1}{\rm Mpc}$, which is consistent with our precious result. We find a clear signal of the `Finger-of-God' effect on the 2D correlation function of the whole sample, which indicates the random peculiar motion of central bright galaxies in the gravitation potential well of clusters.
We present the results of our investigations into options for the computing platform for the imaging pipeline in the CHILES project, an ultra-deep HI pathfinder for the era of the Square Kilometre Array. CHILES pushes the current computing infrastructure to its limits and understanding how to deliver the images from this project is clarifying the Science Data Processing requirements for the SKA. We have tested three platforms: a moderately sized cluster, a massive High Performance Computing (HPC) system, and the Amazon Web Services (AWS) cloud computing platform. We have used well-established tools for data reduction and performance measurement to investigate the behaviour of these platforms for the complicated access patterns of real-life Radio Astronomy data reduction. All of these platforms have strengths and weaknesses and the system tools allow us to identify and evaluate them in a quantitative manner. With the insights from these tests we are able to complete the imaging pipeline processing on both the HPC platform and also on the cloud computing platform, which paves the way for meeting big data challenges in the era of SKA in the field of Radio Astronomy. We discuss the implications that all similar projects will have to consider, in both performance and costs, to make recommendations for the planning of Radio Astronomy imaging workflows.
By comparing a magneto-frictional model of the low coronal magnetic field to a potential-field source-surface model, we investigate the possible impact of non-potential magnetic structure on empirical solar-wind models. These empirical models (such as Wang-Sheeley-Arge) estimate the distribution of solar-wind speed solely from the magnetic-field structure in the low corona. Our models are computed in a domain between the solar surface and 2.5 solar radii, and are extended to 0.1 AU using a Schatten current-sheet model. The non-potential field has a more complex magnetic skeleton and quasi-separatrix structures than the potential field, leading to different sub-structure in the solar-wind speed proxies. It contains twisted magnetic structures that can perturb the separatrix surfaces traced down from the base of the heliospheric current sheet. A significant difference between the models is the greater amount of open magnetic flux in the non-potential model. Using existing empirical formulae this leads to higher predicted wind speeds for two reasons: partly because magnetic flux tubes expand less rapidly with height, but more importantly because more open field lines are further from coronal-hole boundaries.
We report a new sample of obscured active galactic nuclei (AGNs) selected from the XMM serendipitous source and AKARI point-source catalogs. We match X-ray sources with infrared (18 and 90 micron) sources located at |b|>10 deg to create a sample consisting of 173 objects. Their optical classifications and absorption column densities measured by X-ray spectra are compiled and study efficient selection criteria to find obscured AGNs. We apply the criteria (1) X-ray hardness ratio defined by using the 2-4.5 keV and 4.5-12 keV bands >-0.1 and (2) EPIC-PN count rate (CR) in the 0.2-12 keV to infrared flux ratio CR/F90<0.1 or CR/F18<1, where F18 and F90 are infrared fluxes at 18 and 90 micron in Jy, respectively, to search for obscured AGNs. X-ray spectra of 48 candidates, for which no X-ray results have been published, are analyzed and X-ray evidence for the presence of obscured AGNs such as a convex shape X-ray spectrum indicative of absorption of NH~10^{22-24} cm^-2, a very flat continuum, or a strong Fe-K emission line with an equivalent width of >700 eV is found in 26 objects. Six among them are classified as Compton-thick AGNs, and four are represented by either Compton-thin or Compton-thick spectral models. The success rate of finding obscured AGNs combining our analysis and the literature is 92% if the 18 micron condition is used. Of the 26 objects, 4 are optically classified as an HII nucleus and are new "elusive AGNs" in which star formation activity likely overwhelms AGN emission in the optical and infrared bands.
In a companion paper we have constructed a new statistical model for blazar populations, which reproduces the apparent velocity and redshift distributions from the MOJAVE survey while assuming single power law distributions for the Lorentz factors and the unbeamed monochromatic radio luminosity. Treating two separate cases, one for the BL Lac objects (BL Lacs) and one for the Flat Spectrum Radio Quasars (FSRQs), we calculated the distribution of the timescale modulation factor $\Delta t'/\Delta t$ which quantifies the change in observed timescales compared to the rest-frame ones due to redshift and relativistic compression. We found that $\Delta t'/\Delta t$ follows an exponential distribution with a mean depending on the flux limit of the sample, for both classes. In this work we produce the mathematical formalism that allows us to use this information in order to uncover the underlining rest-frame probability density function (PDF) of observable/measurable timescales of blazar jets, by fitting their observed probability density function. We test our proposed methodology extensively using simulated data, and identify limits of applicability and potential biases due to observational systematics and sample selection.
Compact steep spectrum (CSS) and GHz-peaked spectrum (GPS) radio sources represent a large fraction of the extragalactic objects in flux density-limited samples. They are compact, powerful radio sources whose synchrotron peak frequency ranges between a few hundred MHz to several GHz. CSS and GPS radio sources are currently interpreted as objects in which the radio emission is in an early evolutionary stage. In this contribution I review the radio properties and the physical characteristics of this class of radio sources, and the interplay between their radio emission and the ambient medium of the host galaxy.
The last comprehensive catalogue of high-mass X-ray binaries in the Small Magellanic Cloud (SMC) was published about 10 years ago. Since then new such systems were discovered, mainly by X-ray observations with Chandra and XMM-Newton. For the majority of the proposed HMXBs in the SMC no X-ray pulsations were discovered yet and unless other properties of the X-ray source and/or the optical counterpart confirm their HMXB nature, they remain only candidate HMXBs. From a literature search we collect a catalogue of 148 confirmed and candidate HMXBs in the SMC and investigate their properties to shed light on their real nature. Based on the sample of well established HMXBs (the pulsars), we investigate which observed properties are most appropriate for a reliable classification. Using spectral and temporal characteristics of the X-ray sources and colour-magnitude diagrams from the optical to the infrared of their likely counterparts and taking into account the uncertainty in the X-ray position we define different levels of confidence for being a genuine HMXB. From the lack of an infrared excess of the proposed counterpart, mainly for X-ray sources with large positional uncertainty, and using additional information obtained from more recent observations, we identify 27 objects as likely mis-identifications. This results in a catalogue of 121 relatively high-confidence HMXBs (the vast majority with Be companion stars) with about half of the objects showing X-ray pulsations while for the rest no pulsations are known yet. A comparison of the two subsamples suggests that long pulse periods in excess of a few 100 s are expected for the "non-pulsars", which are likely undetected because of aperiodic variability on similar time scales and insufficiently long X-ray observations. (abbreviated)
No Hadean rocks have ever been found on Earth's surface except for zircons---evidence of continental crust, suggesting that Hadean continental crust existed but later disappeared. One hypothesis for the disappearance of the continental crust is excavation/melting by the Late Heavy Bombardment (LHB), a concentration of impacts in the last phase of the Hadean eon. In this paper, we calculate the effects of LHB on Hadean continental crust in order to investigate this hypothesis. Approximating the size-frequency distribution of the impacts by a power-law scaling with an exponent {\alpha} as a parameter, we have derived semi-analytical expressions for the effects of LHB impacts. We calculated the total excavation/melting volume and area affected by the LHB from two constraints of LHB on the moon, the size of the largest basin during LHB, and the density of craters larger than 20 km. We also investigated the effects of the value of {\alpha}. Our results show that LHB does not excavate/melt all of Hadean continental crust directly, but over 70% of the Earth's surface area can be covered by subsequent melts in a broad range of {\alpha}. If there have been no overturns of the continental crust until today, LHB could be responsible for the absence of Hadean rocks because most of Hadean continental crust is not be exposed on the Earth's surface in this case.
[abridged] How does a star cluster of more than few 10,000 solar masses form? We present the case of the cluster NGC 346 in the Small Magellanic Cloud, and its star-forming region N66, and we propose a scenario for its formation, based on observations of the rich stellar populations in the region. Young massive clusters (YMCs) host a high fraction of early-type stars, indicating an extremely high star formation efficiency. The Magellanic Clouds host a wide range of such clusters with the youngest being still embedded in their giant HII regions. Hubble Space Telescope imaging of such star-forming complexes allows the detailed study of star formation at scales typical for molecular clouds. Our cluster analysis of newly-born stars in N66 shows that star formation in the region proceeds in a clumpy hierarchical fashion, leading to the formation of both a dominant YMC, hosting about half of the observed pre--main-sequence population, and a dispersed self-similar distribution of the remaining stars. We investigate the correlation between star formation rate derived from star-counts and molecular gas surface density in order to unravel the physical conditions that gave birth to NGC 346. We find a steep correlation between these two parameters with a considerable scatter. The fraction of mass in stars is found to be systematically higher within the central 15 pc (where the YMC is located) than outside, which suggests variations in the star formation efficiency within the same star-forming complex. This trend possibly reflects a change of star formation efficiency in N66 between clustered and non-clustered star formation. Our findings suggest that the formation of NGC 346 is the combined result of star formation regulated by turbulence and of early dynamical evolution induced by the gravitational potential of the dense interstellar medium.
Following the discovery of the cosmic rays by Victor Hess in 1912, more than 70 years and numerous technological developments were needed before an unambiguous detection of the first very-high-energy gamma-ray source in 1989 was made. Since this discovery the field on very-high-energy gamma-ray astronomy experienced a true revolution: A second, then a third generation of instruments were built, observing the atmospheric cascades from the ground, either through the atmospheric Cherenkov light they comprise, or via the direct detection of the charged particles they carry. Present arrays, 100 times more sensitive than the pioneering experiments, have detected a large number of astrophysical sources of various types, thus opening a new window on the non-thermal Universe. New, even more sensitive instruments are currently being built; these will allow us to explore further this fascinating domain. In this article we describe the detection techniques, the history of the field and the prospects for the future of ground-based very-high-energy gamma-ray astronomy.
Superfireballs are rare phenomena for which the reports are scarce and the estimation of their abundance has a huge margin of uncertainty. As a citizen science project we have gathered >500 reports from newspapers in the 1850-2000 period. This database shows how some superfireball abundances are constant during the period, though the reference newspapers have changed in the last two centuries. We have tentatively related some fireball sources to well-known meteor showers (Perseids, Geminids and Leonids), while superfireball sources may be related to minor or unknown showers, probably of asteroidal origin.
Aims: By utilising spectra of early-type stellar probes of known distances in the same region of the sky, the large and small-scale (pc) structure of the Galactic ISM can be investigated. This paper determines the variation in line strength of CaII at 3933.661 A, as a function of probe separation for a sample of stars, including many sightlines in the Magellanic Clouds. Methods: FLAMES-GIRAFFE data taken with the VLT towards early-type stars in 3 Galactic & 4 Magellanic open clusters in CaII are used to obtain the velocity, EW, column density and line width of IS Galactic Ca for a total of 657 stars, of which 443 are Magellanic sightlines. In each cluster there are 43-110 stars observed. Additionally, FEROS and UVES CaII & NaI spectra of 21 Galactic & 154 Magellanic early-type stars are presented and combined with data from the literature to study the Ca column density/parallax relationship. Results: For the four Magellanic clusters studied with FLAMES, the strength of the Galactic IS CaII K EW over transverse scales from 0.05-9 pc is found to vary by factors of 1.8-3.0, corresponding to column density variations of 0.3-0.5 dex in the optically-thin approximation. Using FLAMES, FEROS and UVES archive spectra, the min and max reduced EW for MW gas is found to lie in the range 35-125 mA & 30-160 mA for CaII K and NaI D, respectively. The range is consistent with a simple model of the ISM published by van Loon et al. (2009) consisting of spherical cloudlets of filling factor 0.3, although other geometries are not ruled out. Finally, the derived functional form for parallax and CaII column density is found to be pi(mas)=1/(2.39e-13 x N(CaII)(cm-2)+0.11). Our derived parallax is 25 per cent lower than predicted by Megier et al. (2009) at a distance of 100 pc and 15% lower at a distance of 200 pc, reflecting inhomogeneity in the CaII distribution in the different sightlines studied.
Three giant flares have been detected so far from soft gamma-ray repeaters, each characterized by an initial short hard spike and a pulsating tail. The observed pulsating tails are characterized by a duration of $\sim100\,\rm{s}$, an isotropic energy of $\sim 10^{44}\,\rm{erg}$, and a pulse period of a few seconds. The pulsating tail emission likely originates from the residual energy after the intense energy release during the initial spike, which forms a trapped fireball composed of a photon-pair plasma in a closed field line region of the magnetars. Observationally the spectra of pulsating tails can be fitted by the superposition of a thermal component and a power-law component, with the thermal component dominating the emission in the early and late stages of the pulsating tail observations. In this paper, assuming that the trapped fireball is from a closed field line region in the magnetosphere, we calculate the atmosphere structure of the optically-thick trapped fireball and the polarization properties of the trapped fireball. By properly treating the photon propagation in a hot, highly magnetized, electron-positron pair plasma, we tally photons in two modes (O mode and E mode) at a certain observational angle through Monte Carlo simulations. Our results suggest that the polarization degree depends on the viewing angle with respect to the magnetic axis of the magnetar, and can be as high as $\Pi\simeq30\%$ in the $1-30\,\rm{keV}$ band, and $\Pi\simeq10\%$ in the $30-100\,\rm{keV}$ band, if the line of sight is perpendicular to the magnetic axis.
Mg II lines represent one of the strongest emissions from the chromospheric plasma during solar flares. In this article, we studied the Mg II lines observed during the X1 flare on March 29 2014 (SOL2014-03-29T17:48) by IRIS. IRIS detected large intensity enhancements of the Mg II h and k lines, subordinate triplet lines, and several other metallic lines at the flare footpoints during this flare. We have used the advantage of the slit-scanning mode (rastering) of IRIS and performed, for the first time, a detailed analysis of spatial and temporal variations of the spectra. Moreover, we were also able to identify positions of strongest HXR emissions using RHESSI observations and to correlate them with the spatial and temporal evolution of Mg II spectra. The light curves of the Mg II lines increase and peak contemporarily with the HXR emissions but decay more gradually. There are large red asymmetries in the Mg II h and k lines after the flare peak. We see two spatially well separated groups of Mg II line profiles, non-reversed and reversed. In some cases, the Mg II footpoints with reversed profiles are correlated with HXR sources. We show the spatial and temporal behavior of several other line parameters (line metrics) and briefly discuss them. Finally, we have synthesized the Mg II k line using our non-LTE code with the MALI technique. Two kinds of models are considered, the flare model F2 of Machado et al. (1980) and the models of Ricchiazzi and Canfield (1983). Model F2 reproduces the peak intensity of the unreversed Mg II k profile at flare maximum but does not account for high wing intensities. On the other hand, the RC models show the sensitivity of Mg II line intensities to various electron-beam parameters. Our simulations also show that the microturbulence produces a broader line core, while the intense line wings are caused by an enhanced line source function.
We propose a new concept for spectral characterization of transiting exoplanets with future space-based telescopes. This concept, called as densified pupil spectroscopy, allows us to perform high, stable spectrophotometry against telescope pointing jitter and deformation of the primary mirror instead of not having imaging capability. This densified pupil spectrometer comprises the following three roles: division of a pupil into a number of sub-pupils, densification of each sub-pupil, and acquisition of the spectrum of each sub-pupil with a conventional spectrometer. Focusing on the fact that the divided and densified sub-pupil can be treated as a point source, we discovered that a simplified spectrometer allows us to acquire the spectra of the densified sub-pupils on the detector plane-an optical conjugate with the primary mirror-by putting the divided and densified sub-pupils on the entrance slit of the spectrometer. The acquired multiple spectra are not principally moved on the detector against the pointing jitter and the reliability of the observation result is also increased by statistically treating them. Our numerical calculations show that this method potentially suppresses the instrumental systematic error caused by the telescope pointing jitter down to the same level of photon noise as one-hour integration on a cryogenic telescope with a diameter of 2.5m at 10um. Because future cryogenic large telescopes such as the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) and the Cryogenic Aperture Large Infrared Space Observatory (CALISTO) will provide us with a thermally stable environment and a low background, they potentially present the first opportunity to characterize the thermal emissions from terrestrial planets.
AGN feedback from supermassive black holes (SMBHs) at the center of early type galaxies is commonly invoked as the explanation for the quenching of star formation in these systems. The situation is complicated by the significant amount of mass injected in the galaxy by the evolving stellar population over cosmological times. In absence of feedback, this mass would lead to unobserved galactic cooling flows, and to SMBHs two orders of magnitude more massive than observed. By using high-resolution 2D hydrodynamical simulations with radiative transport and star formation in state-of-the-art galaxy models, we show how the intermittent AGN feedback is highly structured on spatial and temporal scales, and how its effects are not only negative (shutting down the recurrent cooling episodes of the ISM), but also positive, inducing star formation in the inner regions of the host galaxy.
The solar wind electric sail (E-sail) is a planned in-space propulsion device that uses the natural solar wind momentum flux for spacecraft propulsion with the help of long, charged, centrifugally stretched tethers. The problem of accurately predicting the E-sail thrust is still somewhat open, however, due to a possible electron population trapped by the tether. Here we develop a new type of particle-in-cell (PIC) simulation for predicting E-sail thrust. In the new simulation, electrons are modelled as a fluid, hence resembling hydrid simulation, but in contrast to normal hybrid simulation, the Poisson equation is used as in normal PIC to calculate the self-consistent electrostatic field. For electron-repulsive parts of the potential, the Boltzmann relation is used. For electron-attractive parts of the potential we employ a power law which contains a parameter that can be used to control the number of trapped electrons. We perform a set of runs varying the parameter and select the one with the smallest number of trapped electrons which still behaves in a physically meaningful way in the sense of producing not more than one solar wind ion deflection shock upstream of the tether. By this prescription we obtain thrust per tether length values that are in line with earlier estimates, although somewhat smaller. We conclude that the Boltzmann PIC simulation is a new tool for simulating the E-sail thrust. This tool enables us to calculate solutions rapidly and allows to easily study different scenarios for trapped electrons.
Early-type galaxies (ETGs) host a hot ISM produced mainly by stellar winds, and heated by Type Ia supernovae and the thermalization of stellar motions. High resolution 2D hydrodynamical simulations showed that ordered rotation in the stellar component results in the formation of a centrifugally supported cold equatorial disc. In a recent numerical investigation we found that subsequent generations of stars are formed in this cold disc; this process consumes most of the cold gas, leaving at the present epoch cold masses comparable to those observed. Most of the new stellar mass formed a few Gyrs ago, and resides in a disc.
Data from the PAMELA satellite experiment were used to measure the geomagnetic cutoff for high-energy ($\gtrsim$ 80 MeV) protons during the solar particle events on 2006 December 13 and 14. The variations of the cutoff latitude as a function of rigidity were studied on relatively short timescales, corresponding to single spacecraft orbits (about 94 minutes). Estimated cutoff values were cross-checked with those obtained by means of a trajectory tracing approach based on dynamical empirical modeling of the Earth's magnetosphere. We find significant variations in the cutoff latitude, with a maximum suppression of about 6 deg for $\sim$80 MeV protons during the main phase of the storm. The observed reduction in the geomagnetic shielding and its temporal evolution were compared with the changes in the magnetosphere configuration, investigating the role of IMF, solar wind and geomagnetic (Kp, Dst and Sym-H indexes) variables and their correlation with PAMELA cutoff results.
We quantify the contamination from polarized diffuse Galactic synchrotron and thermal dust emissions to the B-modes of the CMB anisotropies on the degree angular scale, using data from the Planck and WMAP satellites. We compute power spectra of foreground polarized emissions in 352 circular sky patches located at Galactic latitude |b|>20{\deg}, each of which covering a fraction of the sky of about 1.5%. We make use of the spectral properties derived from Planck and WMAP data to extrapolate, in frequency, the amplitude of synchrotron and thermal dust B-modes spectra in the multipole bin centered at $\ell\simeq80$. In this way we estimate, for each analyzed region, the amplitude and frequency of the foreground minimum. We detect both dust and synchrotron signal, at degree angular scale and at 3 confidence level, in 28 regions. Here the minimum of the foreground emission is found at frequencies between 60 and 100 GHz with an amplitude,expressed in terms of the equivalent tensor-to-scalar ratio, r_FG, between ~0.06 and ~1. Some of these regions are located at high Galactic latitudes, in areas close to the ones which are being observed by sub-orbital experiments.In all the other sky patches, where synchrotron or dust B-modes are not detectable with the required confidence, we put upper limits on the minimum foreground contamination and find values of r_FG between ~0.05 and ~1.5, in the frequency range 60-90 GHz. Our results indicate that, with the current sensitivity at low frequency, it is not possible to exclude the presence of synchrotron contamination to CMB cosmological B-modes at the level requested to measure a gravitational waves signal with r~0.01, at frequency <100 GHz, anywhere. Therefore, more accurate data are essential in order to better characterize the synchrotron polarized component, and eventually, remove its contamination to CMB signal through foreground cleaning.
Recently, compact black hole X-ray binaries XTE J 1118+480 and A0620-00 have been reported to be experiencing a fast orbital period decay, which is two orders of magnitude higher than expected with gravitational wave radiation. Magnetic braking of an Ap/Bp star has been suggested to account for the period change when the surface magnetic field of the companion star $B_{\rm s}\ga 10^{4}$ G. However, our calculation indicates that anomalous magnetic braking cannot significantly contribute to the large orbital period decay rates observed in these two sources even if $B_{\rm s}\ga 10^{4}$ G. Observations have provided evidence that circumbinary disks around two compact black hole X-ray binaries may exist. Our analysis shows that, for some reasonable parameters, tidal torque between the circumbinary disk and the binary can efficiently extract the orbital angular momentum from the binary, and result in a large orbital period change rate. Based on the circumbinary disk model, we simulate the evolution of XTE J 1118+480 via a stellar evolution code. Our computations are approximatively in agreement with the observed data (the masses of two components, donor star radius, orbital period, and orbital period derivative). The mass transfer rate and circumbinary disk mass are obviously far greater than the inferred values from observations. Therefore, it seems that the circumbinary disk is unlikely to be the main cause of the rapid orbital decay observed in some compact black hole X-ray binaries.
Data from the PAMELA satellite experiment were used to perform a detailed measurement of under-cutoff protons at low Earth orbits. On the basis of a trajectory tracing approach using a realistic description of the magnetosphere, protons were classified into geomagnetically trapped and re-entrant albedo. The former include stably-trapped protons in the South Atlantic Anomaly, which were analyzed in the framework of the adiabatic theory, investigating energy spectra, spatial and angular distributions; results were compared with the predictions of the AP8 and the PSB97 empirical trapped models. The albedo protons were classified into quasi-trapped, concentrating in the magnetic equatorial region, and un-trapped, spreading over all latitudes and including both short-lived (precipitating) and long-lived (pseudo-trapped) components. Features of the penumbra region around the geomagnetic cutoff were investigated as well. PAMELA observations significantly improve the characterization of the high energy proton populations in near Earth orbits.
Rotation periods are increasingly being used to derive ages for cool single field stars. Such ages are based on an empirical understanding of how cool stars spin down, acquired by constructing color-period diagrams (CPDs) for a series of open clusters. Our main aims here are to construct a CPD for M 48, to compare this with other clusters of similar age to check for consistency, and to derive a rotational age for M 48 using gyrochronology. We monitored M 48 photometrically for over 2 months with AIP's STELLA I 1.2 m telescope and the WiFSIP 4K imager in Tenerife. Light curves with 3 mmag precision for bright (V~14 mag) stars were produced and then analysed to provide rotation periods. A cluster CPD has then been constructed. We report 62 rotation periods for cool stars in M 48. The CPD displays a clear slow/I-sequence of rotating stars, similar to those seen in the 625 Myr-old Hyades and 590 Myr-old Praesepe clusters, and below both, confirming that M 48 is younger. A similar comparison with the 250 Myr-old M 34 cluster shows that M 48 is older and does not possess any fast/C-sequence G or early K stars like those in M 34, although relatively fast rotators do seem to be present among the late-K and M stars. A more detailed comparison of the CPD with rotational evolution models shows that the cluster stars have a mean age of 450 Myr, and its (rotating) stars can be individually dated to +-117 Myr (26%). Much of this uncertainty stems from intrinsic astrophysical spread in initial periods, and almost all stars are consistent with a single age of 450 Myr. The gyro-age of M 48 as a whole is 450+-50 Myr, in agreement with the previously determined isochrone age of 400+-100 Myr.
We performed the first spectral-line survey at 82--106 GHz and 335--355 GHz toward the outflow-shocked region, OMC 2-FIR 4, the outflow driving source, FIR 3, and the northern outflow lobe, FIR 3N. We detected 120 lines of 20 molecular species. The line profiles are found to be classifiable into two types: one is a single Gaussian component with a narrow ($<$ 3 km s$^{-1}$) width and another is two Gaussian components with narrow and wide ($>$ 3km s$^{-1}$) widths. The narrow components for the most of the lines are detected at all positions, suggesting that they trace the ambient dense gas. For CO, CS, HCN, and HCO$^{+}$, the wide components are detected at all positions, suggesting the outflow origin. The wide components of C$^{34}$S, SO, SiO, H$^{13}$CN, HC$^{15}$N, H$_2^{13}$CO, H$_2$CS, HC$_3$N, and CH$_3$OH are detected only at FIR 4, suggesting the outflow-shocked gas origin. The rotation diagram analysis revealed that the narrow components of C$_2$H and H$^{13}$CO$^+$ show low temperatures of 12.5$\pm$1.4 K, while the wide components show high temperatures of 20--70 K. This supports our interpretation that the wide components trace the outflow and/or outflow-shocked gas. We compared observed molecular abundances relative to H$^{13}$CO$^+$ with those of the outflow-shocked region, L1157 B1, and the hot corino, IRAS 16293-2422. Although we cannot exclude a possibility that the chemical enrichment in FIR 4 is caused by the hot core chemistry, the chemical compositions in FIR 4 are more similar to those in L1157 B1 than those in IRAS 16293-2422.
Rotationally fissioned asteroids produce unbound daughter asteroids that have very similar heliocentric orbits. Backward integration of their current heliocentric orbits provides an age of closest proximity that can be used to date the rotational fission event. Most asteroid pairs follow a predicted theoretical relationship between the primary spin period and the mass ratio of the two pair members that is a direct consequence of the YORP-induced rotational fission hypothesis. If the progenitor asteroid has strength, asteroid pairs may have high mass ratios with possibly fast rotating primaries. However, secondary fission leaves the originally predicted trend unaltered. We also describe the characteristics of pair members produced by four alternative routes from a rotational fission event to an asteroid pair. Unlike direct formation from the event itself, the age of closest proximity of these pairs cannot generally be used to date the rotational fission event since considerable time may have passed.
At present, the best model for the evolution of the cosmos requires that dark matter makes up approximately 25% of the energy content of the Universe. Most approaches to explain the microscopic nature of dark matter, to date, have assumed its composition to be of intrinsically weakly-interacting particles; however, this need not be the case to have consistency with all extant observations. Given decades of no conclusive evidence to support any dark matter candidate so far, there is strong motivation to consider alternatives to the standard particle scenario. One such example is macro dark matter, a class of candidates that could interact quite strongly with the particles of the Standard Model, have large masses and physical sizes, yet behave as dark matter. Here we reconsider the effect of inelastically interacting macro dark matter on the abundance of primordially produced $^4\text{He}$, revising older constraints by both revisiting the phenomenology and taking into account recent improved measurements of the primordial $^4\text{He}$ abundance. An important aspect of our analysis is that even neutral Macros could affect the abundance of the light elements because, due to differences in their masses, those elements would be absorbed at rates that differ from each other by order unity.
We present a five-band Herschel study (100-500um) of three galaxy clusters at z~1.2 from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS). With a sample of 120 spectroscopically-confirmed cluster members, we investigate the role of environment on galaxy properties utilizing the projected cluster phase space (line-of-sight velocity versus clustercentric radius), which probes the time-averaged galaxy density to which a galaxy has been exposed. We divide cluster galaxies into phase-space bins of (r/r200) x (v/sigma_v), tracing a sequence of accretion histories in phase space. Stacking optically star-forming cluster members on the Herschel maps, we measure average infrared star formation rates, and, for the first time in high-redshift galaxy clusters, dust temperatures for dynamically distinct galaxy populations---namely, recent infalls and those that were accreted onto the cluster at an earlier epoch. Proceeding from the infalling to virialized (central) regions of phase space, we find a steady decrease in the specific star formation rate and increase in the stellar age of star-forming cluster galaxies. We perform a probability analysis to investigate all acceptable infrared spectral energy distributions within the full parameter space and measure a ~4 sigma drop in the average dust temperature of cluster galaxies in an intermediate phase-space bin, compared to an otherwise flat trend with phase space. We suggest one plausible quenching mechanism which may be consistent with these trends, invoking ram-pressure stripping of the warmer dust for galaxies within this intermediate accretion phase.
We show that simple thermodynamic conditions determine, to a great extent, the equation of state and dynamics of cosmic defects of arbitrary dimensionality. We use these conditions to provide a more direct derivation of the Velocity-dependent One-Scale (VOS) model for the macroscopic dynamics of topological defects of arbitrary dimensionality in a $N+1$-dimensional homogeneous and isotropic universe. We parameterize the modifications to the VOS model associated to the interaction of the topological defects with other fields, including, in particular, a new dynamical degree of freedom associated to the variation of the mass per unit $p$-area of the defects, and compute the corresponding scaling solutions. The observational impact of this new dynamical degree of freedom is also briefly discussed.
We perform a computational survey of possible post-collision mass distributions in high-speed galaxy cluster collisions in the presence of weakly self-interacting dark matter. We show that astrophysically weak self-interactions of dark matter may impart subtle yet measurable structures to the distribution of mass in high-speed collision galaxy clusters without significantly disrupting the colliding galaxy clusters or their dark matter halos. Interesting structures appear in the projected mass density maps of collision galaxy clusters as dark matter concentrations at large scattering angles and the distances from the collision center commensurate with that of the outgoing galaxy groups. Convincing observation of such structures would be a clear indication of the self-interacting nature of dark matter, as purely gravitational effects in high-speed galaxy cluster collisions are observed to produce material ejecta only in the forward and the backward cones around the collision axis. Our simulations indicate that as much as 20% of the total collision cluster mass may be deposited to produce such structures without noticeably disrupting the participating galaxy clusters or their dark matter halos. Our findings appear to explain the ring-like dark matter feature recently observed in long-range reconstructions of the mass density profile of the collision galaxy cluster CL0024+017. The size of this feature implies an estimate for the dark matter self-interaction strength of $\sigma_{DM}/m_{DM} \approx 0.1\ cm^2/g$.
Using all the observations from Rossi X-ray Timing Explorer for Z source GX 349+2, we systematically carry out cross-correlation analysis between its soft and hard X-ray light curves. During the observations from January 9 to January 29, 1998, GX 349+2 traced out the most extensive Z track on its hardness-intensity diagram, making a comprehensive study of cross-correlation on the track. The positive correlations and positively correlated time lags are detected throughout the Z track. Outside the Z track, anti-correlations and anti-correlated time lags are found, but the anti-correlated time lags are much longer than the positively correlated time lags, which might indicate different mechanisms for producing the two types of time lags. We argue that neither the short-term time lag models nor the truncated accretion disk model can account for the long-term time lags in neutron star low mass X-ray binaries (NS-LMXBs). We suggest that the extended accretion disk corona model could be an alternative model to explain the long-term time lags detected in NS-LMXBs.
While giant extrasolar planets have been studied for more than two decades now, there are still some open questions such as their dominant formation and migration process, as well as their atmospheric evolution in different stellar environments. In this paper, we study a sample of giant transiting exoplanets detected by the Kepler telescope with orbital periods up to 400 days. We first defined a sample of 129 giant-planet candidates that we followed up with the SOPHIE spectrograph (OHP, France) in a 6-year radial velocity campaign. This allow us to unveil the nature of these candidates and to measure a false-positive rate of 54.6 +/- 6.5 % for giant-planet candidates orbiting within 400 days of period. Based on a sample of confirmed or likely planets, we then derive the occurrence rates of giant planets in different ranges of orbital periods. The overall occurrence rate of giant planets within 400 days is 4.6 +/- 0.6 %. We recover, for the first time in the Kepler data, the different populations of giant planets reported by radial velocity surveys. Comparing these rates with other yields, we find that the occurrence rate of giant planets is lower only for hot jupiters but not for the longer period planets. We also derive a first measurement on the occurrence rate of brown dwarfs in the brown-dwarf desert with a value of 0.29 +/- 0.17 %. Finally, we discuss the physical properties of the giant planets in our sample. We confirm that giant planets receiving a moderate irradiation are not inflated but we find that they are in average smaller than predicted by formation and evolution models. In this regime of low-irradiated giant planets, we find a possible correlation between their bulk density and the Iron abundance of the host star, which needs more detections to be confirmed.
We derive the mean wavelength dependence of stellar attenuation in a sample of 239 high redshift (1.90 < z < 2.35) galaxies selected via Hubble Space Telescope (HST) WFC3 IR grism observations of their rest-frame optical emission lines. Our analysis indicates that the average reddening law follows a form similar to that derived by Calzetti et al. for local starburst galaxies. However, over the mass range 7.2 < log M/Msolar < 10.2, the slope of the attenuation law in the UV is shallower than that seen locally, and the UV slope steepens as the mass increases. These trends are in qualitative agreement with Kriek & Conroy, who found that the wavelength dependence of attenuation varies with galaxy spectral type. However, we find no evidence of an extinction "bump" at 2175 A in any of the three stellar mass bins, or in the sample as a whole. We quantify the relation between the attenuation curve and stellar mass and discuss its implications.
We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster galaxies, with r-band monochromatic luminosity L_r=8-14L* (4.3-7.5E44 erg/s). These super spiral galaxies are also giant and massive, with diameter D=57-134 kpc and stellar mass M_stars=0.3-3.4E11 M_sun. We find 53 super spirals out of a complete sample of 1,616 SDSS galaxies with redshift z<0.3 and L_r>8L*. The closest example is found at z=0.089. We use existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS and WISE colors are consistent with normal star-forming spirals on the blue sequence. However, the extreme masses and rapid SFRs of 5-65 M_sun/yr place super spirals in a sparsely populated region of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a diverse range of environments, from isolation to cluster centers. We find four super spiral galaxy systems that are late-stage major mergers--a possible clue to their formation. We suggest that super spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become massive lenticular galaxies after they are cut off from their gas supply and their disks fade.
The density field reconstruction technique, which was developed to partially reverse the nonlinear degradation of the Baryon Acoustic Oscillation (BAO) feature in the galaxy redshift surveys, has been successful in substantially improving the cosmology constraints from recent galaxy surveys such as Baryon Oscillation Spectroscopic Survey (BOSS). We estimate the efficiency of the reconstruction method as a function of various reconstruction details. To directly quantify the BAO information in nonlinear density fields before and after reconstruction, we calculate the cross-correlations (i.e., propagators) of the pre(post)-reconstructed density field with the initial linear field using a mock galaxy sample that is designed to mimic the clustering of the BOSS CMASS galaxies. The results directly provide the BAO damping as a function of wavenumber that can be implemented into the Fisher matrix analysis. We focus on investigating the dependence of the propagator on a choice of smoothing filters and on two major different conventions of the redshift-space density field reconstruction that have been used in literature. By estimating the BAO signal-to-noise for each case, we predict constraints on the angular diameter distance and Hubble parameter using the Fisher matrix analysis. We thus determine an optimal Gaussian smoothing filter scale for the signal-to-noise level of the BOSS CMASS. We also present appropriate BAO fitting models for different reconstruction methods based on the first and second order Lagrangian perturbation theory in Fourier space. Using the mock data, we show that the modified BAO fitting model can substantially improve the accuracy of the BAO position in the best fits as well as the goodness of the fits.
We present our imaging and spectroscopic observations of the host galaxies of
two dark long bursts with anomalously high metallicities, LGRB 051022 and LGRB
020819B, which in conjunction with another LGRB event with an optical afterglow
comprise the three LGRBs with high metallicity host galaxies in the Graham &
Fruchter (2013) sample. In Graham & Fruchter (2013), we showed that LGRBs
exhibit a strong and apparently intrinsic preference for low metallicity
environments (12+log(O/H) < 8.4 in the KK04 scale) in spite of these three
cases with abundances of about solar and above. These exceptions however are
consistent with the general star-forming galaxy population of comparable
brightness & redshift. This is surprising: even among a preselected sample of
high metallicity LGRBs, were the metal aversion to remain in effect for these
objects, we would expect their metallicity to still be lower than the typical
metallicity for the galaxies at that luminosity and redshift. Therefore we
deduce that it is possible to form an LGRB in a high metallicity environment
although with greater rarity.
From this we conclude that there are three possible explanations for the
presence of the LGRBs observed in high metallicity hosts as seen to date: (1)
LGRBs do not occur in high metallicity environments and those seen in high
metallicity hosts are in fact occurring in low metallicity environments that
have become associated with otherwise high metallicity hosts but remain
unenriched. (2) The LGRB formation mechanism while preferring low metallicity
environments does not strictly require it resulting in a gradual decline in
burst formation with increasing metallicity. (3) The typical low metallicity
LGRBs and the few high metallicity cases are the result of physically different
burst formation pathways with only the former affected by the metallicity and
the later occurring much more infrequently.
We consider the case of very low reheating scenarios ($T_{\rm RH}\sim\mathcal{O}({\rm MeV})$) with a better calculation of the production of the relic neutrino background (with three-flavor oscillations). At 95% confidence level, a lower bound on the reheating temperature $T_{\rm RH}>4.1$ MeV is obtained from Big Bang Nucleosynthesis, while $T_{\rm RH}>4.3$ MeV from Planck data for very light ($\sum m_i = 0.06$ eV) neutrinos. If neutrino masses are allowed to vary, Planck data yield $T_{\rm RH}>4.7$ MeV, the most stringent bound on the reheating temperature to date. Neutrino masses as large as 1 eV are possible for very low reheating temperatures.
Neutron stars with large masses $\sim 2M_{\odot}$ require the hard stiffness of equation of state (EoS) of neutron-star matter. On the other hand, hyperon mixing brings about remarkable softening of EoS. In order to solve this problem, a multi-pomeron exchange potential (MPP) is introduced as a model for the universal many-body repulsion in baryonic systems on the basis of the Extended Soft Core (ESC) baryon-baryon interaction. The strength of MPP is determined by analyzing the nucleus-nucleus scattering with the G-matrix folding model. The interactions in $\Lambda\!N$, $\Sigma\!N$ and $\Xi\!N$ channels are shown to be consistent with experimental indications. The EoS in neutron-star matter with hyperon mixing is obtained from ESC in addition of MPP, and mass-radius relations of neutron stars are derived. The maximum mass is shown to reach $2M_{\odot}$ even in the case of including hyperon mixing on the basis of model-parameters determined by terrestrial experiments.
While the modern science is characterized by an exponential growth in scientific literature, the increase in publication volume clearly does not reflect the expansion of the cognitive boundaries of science. Nevertheless, most of the metrics for assessing the vitality of science or for making funding and policy decisions are based on productivity. Similarly, the increasing level of knowledge production by large science teams, whose results often enjoy greater visibility, does not necessarily mean that "big science" leads to cognitive expansion. Here we present a novel, big-data method to quantify the extents of cognitive domains of different bodies of scientific literature independently from publication volume, and apply it to 20 million articles published over 60-130 years in physics, astronomy, and biomedicine. The method is based on the lexical diversity of titles of fixed quotas of research articles. Owing to large size of quotas, the method overcomes the inherent stochasticity of article titles to achieve <1% precision. We show that the periods of cognitive growth do not necessarily coincide with the trends in publication volume. Furthermore, we show that the articles produced by larger teams cover significantly smaller cognitive territory than (the same quota of) articles from smaller teams. Our findings provide a new perspective on the role of small teams and individual researchers in expanding the cognitive boundaries of science. The proposed method of quantifying the extent of the cognitive territory can also be applied to study many other aspects of "science of science."
A complete analysis of the dynamics of the Hu-Sawicki modification to General Relativity is presented. In particular, the full phase-space is given for the case in which the model parameters are taken to be n=1, c1=1, and several stable de Sitter equilibrium points together with an unstable "matter-like" point are identified. We find that if the cosmological parameters are chosen to take on their Lambda CDM values today, this results in a universe which, until very low redshifts, is dominated by an equation of state parameter equal t1/3, leading to an expansion history very different from Lambda CDM. We demonstrate that this problem can be resolved by choosing Lambda CDM initial conditions at high redshifts and integrating the equations to the present day.
Modified gravity has attracted much attention over the last few years and remains a potential candidate for dark energy. In particular, the so-called viable f(R) gravity theories, which are able to both recover General Relativity (GR) and produce late-time cosmic acceleration, have been widely studied in recent literature. Nevertheless, extended theories of gravity suffer from several shortcomings which compromise their ability to provide realistic alternatives to the standard cosmological Lambda CDM Concordance model. We address the existence of cosmological singularities and the conditions that guarantee late-time acceleration,assuming reasonable energy conditions for standard matter in the so-called Hu-Sawicki f(R) model, currently among the most widely studied modifications to General Relativity. Then using the Supernovae Ia Union 2.1 catalogue, we further constrain the free parameters of this model. The combined analysis of both theoretical and observational constraints sheds some light on the viable parameter space of these models and the form of the underlying effective theory of gravity.
After giving a brief introduction and presenting a complete classification of gravitational waves (GWs) according to their frequencies, we review and summarize the detection methods, the sensitivities, and the sources. We notice that real-time detections are possible above 300 pHz. Below 300 pHz, the detections are possible on GW imprints or indirectly. We are on the verge of detection. The progress in this field will be promising and thriving. We will see improvement of a few orders to several orders of magnitude in the GW detection sensitivities over all frequency bands in the next hundred years.
We discuss the issue on dark matter capture by neutron stars, in particular the process of dark matter thermalization, by which the scattering cross section and the mass of dark matter can be constrained. At first, we evaluate the thermalization time of self-interacting dark matter and find the effect of the self-interaction is small compared with that of the interaction with nucleons. Then we generalize the thermalization time by introducing a set of new parameters. We show how the cross section is affected by those new parameters. It turns out that the cross section gets very sensitive to and strongly constrained by one of the new parameters.
Nowadays, $f(R)$ theory has been one of the leading modified gravity theories to explain the current accelerated expansion of the universe, without invoking dark energy. It is of interest to find the exact cosmological solutions of $f(R)$ theories. In fact, symmetry has been proved as a powerful tool to find exact solutions in physics. As is well known, Noether symmetry has been extensively used in cosmology and gravity theories. Recently, the so-called Hojman symmetry was also considered in the literature. Hojman symmetry directly deals with the equations of motion, rather than Lagrangian or Hamiltonian, unlike Noether symmetry. In this work, we consider Hojman symmetry in $f(R)$ theories in both the metric and Palatini formalisms, and find the corresponding exact cosmological solutions of $f(R)$ theories via Hojman symmetry. We show that the results are different from the ones obtained by using Noether symmetry in $f(R)$ theories. The present work confirms that Hojman symmetry can bring new features to cosmology and gravity theories.
We consider the application of group invariant transformations in order to constrain a flat isotropic and homogeneous cosmological model, containing of a Brans-Dicke scalar field and a perfect fluid with a constant equation of state parameter $w$, where the latter is not interacting with the scalar field in the gravitational action integral. The requirement that the Wheeler-DeWitt equation be invariant under one-parameter point transformations provides us with two families of power-law potentials for the Brans-Dicke field, in which the powers are functions of the Brans-Dicke parameter $\omega_{BD}$ and the parameter $w$. The existence of the Lie symmetry in the Wheeler-DeWitt equation is equivalent to the existence of a conserved quantity in field equations and with oscillatory terms in the wavefunction of the universe. This enables us to solve the field equations. For a specific value of the conserved quantity, we find a closed-form solution for the Hubble factor, which is equivalent to a cosmological model in general relativity containing two perfect fluids. This provides us with different models for specific values of the parameters $\omega_{BD},$ and $w$. Finally, the results hold for the specific case where the Brans-Dicke parameter $\omega_{BD}$ is zero, that is, for the O'Hanlon massive dilaton theory, and consequently for $f\left( R\right) $-gravity in the metric formalism.
We give a brief review of the non-minimal derivative coupling (NMDC) scalar field theory in which there is non-minimal coupling between the scalar field derivative term and the Einstein tensor. We assume that the expansion is of power-law type or super-acceleration type for small redshift. The Lagrangian includes the NMDC term, a free kinetic term, a cosmological constant term and a barotropic matter term. For a value of the coupling constant that is compatible with inflation, we use the combined WMAP9 (WMAP9+eCMB+BAO+ $H_0$) dataset, the PLANCK+WP dataset, and the PLANCK $TT,TE,EE$+lowP+Lensing+ext datasets to find the value of the cosmological constant in the model. Modeling the expansion with power-law gives a negative cosmological constants while the phantom power-law (super-acceleration) expansion gives positive cosmological constant with large error bar. The value obtained is of the same order as in the $\Lambda$CDM model, since at late times the NMDC effect is tiny due to small curvature.
I suggest that stars introduce mass and density scales that lead to `naturalness' in the Universe. Namely, two ratios of order unity. (1) The combination of the stellar mass scale, M*, with the Planck mass, MPl, and the Chandrasekhar mass leads to a ratio of order unity that reads NPl*=MPl/[(M*)(mp)^2]^{1/3}=0.15-3, where mp is the proton mass. (2) The ratio of the density scale, rhoD = 1/[(G)(tau)^2], introduced by the nuclear life time of stars, tau, to the density of the dark energy, rhoL, is NL*=rhoL/rhoD=10^{-7}-10^{5}. Although the range is large, it is critically much smaller than the 123 orders of magnitude usually referred to when rhoL is compered to the Planck density. In the pure fundamental particles domain there is no naturalness; either naturalness does not exist or there is a need for a new physics or new particles. The `Astrophysical Naturalness' offers a third possibility: stars introduce the combinations of, or relations among, known fundamental quantities that lead to naturalness.
The cosmic rays modulation inside the heliosphere is well described by a transport equation introduced by Parker in 1965. To solve this equation several approaches were followed in the past. Recently the Monte Carlo approach becomes widely used in force of his advantages with respect to other numerical methods. In the Monte Carlo approach, the transport equation is associated to a fully equivalent set of Stochastic Differential Equations. This set is used to describe the stochastic path of a quasi-particle from a source, e.g., the interstellar medium, to a specific target, e.g., a detector at Earth. In this work, we present both the Forward-in-Time and Backward-in-Time Monte Carlo solutions. We present an implementation of both algorithms in the framework of HelMod Code showing that the difference between the two approach is below 5\% that can be quoted as the systematic uncertain of the Method itself.
In this work, we decided to study the Power Law Entropy Corrected Holographic Dark Energy (PLECHDE) model in the framework of a spatially non-flat Universe and in the framework of Ho\v{r}ava-Lifshitz cosmology with infrared (IR) cut-off given by recently proposed Granda-Oliveros cut-off which contains one term proportional to the Hubble parameter squared and one proportional to the time derivative of the Hubble parameter. For the two cases corresponding to non-interacting and interacting DE and Dark Matter (DM), we derive the evolutionary form of the energy density of DE, the Equation of State (EoS) parameter $\omega_D$, the evolutionary form of the fractional energy density $\Omega_D'$ and the deceleration parameter $q$. Using the parametrization of the EoS parameter $\omega_D\left(z\right)=\omega_0+\omega_1 z$, we obtain the expressions of $\omega_0$ and $\omega_1$ for both non-interacting and interacting Dark Sectors. We also study the statefinder parameters $\left\{ r,s \right\}$, the properties of some cosmographic parameters and the squared speed of the sound for the model considered.
It was shown recently that, without jeopardizing the success of the $\Lambda$CDM model on cosmic scales, the MOdified Newtonian Dynamics (MOND) can be derived as an emergent phenomenon when axion-like dark matter particles condense into superfluid on galactic scales. We propose in this letter a Dirac-Born-Infeld (DBI) dark energy conformally coupled to local matter components to solve both galactic and cosmic coincidences that the MOND critical acceleration coincides with present Hubble scale and the matter energy density coincides with dark energy density today. The cosmological evolution of DBI dark energy behaves as a freezing Chaplygin gas and approaches to a cosmological constant in the asymptotic future.
The discrepancy between observed virial and baryonic mass in galaxy clusters have lead to the missing mass problem. To resolve this, a new, non-baryonic matter field, known as dark matter has been invoked. However, till date no possible constituents of the dark matter components are known. This has led to various models, by modifying gravity at large distances to explain the missing mass problem. The modification to gravity appears very naturally when effective field theory on a lower dimensional manifold, embedded in a higher dimensional spacetime is considered. It has been shown that in a scenario with two lower dimensional manifolds separated by a finite distance is capable to address the missing mass problem, which in turn determines the kinematics of the brane separation.
Horndeski models with a de Sitter critical point for any kind of material content may provide a mechanism to alleviate the cosmological constant problem. We study the cosmological evolution of two classes of families - the linear models and the non-linear models with shift symmetry. We conclude that the latter models can deliver a background dynamics compatible with the latest observational data.
Camera image sensors can be used to detect ionizing radiation in addition to optical photons. In particular, cosmic-ray muons are detected as long, straight tracks passing through multiple pixels. The distribution of track lengths can be related to the thickness of the active (depleted) region of the camera image sensor through the known angular distribution of muons at sea level. We use a sample of cosmic-ray muon tracks recorded by the Distributed Electronic Cosmic-ray Observatory to measure the thickness of the depletion region of the camera image sensor in a commercial smart phone, the HTC Wildfire S. The track length distribution prefers a cosmic-ray muon angular distribution over an isotropic distribution. Allowing either distribution, we measure the depletion thickness to be between 13.9~$\mu$m and 27.7~$\mu$m. The same method can be applied to additional models of image sensor. Once measured, the thickness can be used to convert track length to incident polar angle on a per-event basis. Combined with a determination of the incident azimuthal angle directly from the track orientation in the sensor plane, this enables direction reconstruction of individual cosmic-ray events.
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The leakage of Lyman continuum photons from star forming galaxies is an elusive parameter. When observed, it provides a wealth of information on star formation in galaxies and the geometry of the interstellar medium, and puts constraints on the role of star forming galaxies in the reionization of the universe. H-alpha-selected galaxies at z~2 trace the highest star formation population at the peak of cosmic star formation history, providing a base for directly measuring Lyman continuum escape. Here we present this method, and highlight its benefits as well as caveats. We also use the method on 10 H-alpha emitters in the Chandra Deep Field South at z=2.2, also imaged with the Hubble Space Telescope in the ultraviolet. We find no individual Lyman continuum detections, and our stack puts a 5 sigma upper limit on the average absolute escape fraction of <24%, consistent with similar studies. With future planned observations, the sample sizes would rapidly increase and the method presented here would provide very robust constraints on the escape fraction.
Magnetic fields can regulate disk formation, accretion and jet launching. Until recently, it has been difficult to obtain high resolution observations of the magnetic fields of the youngest protostars in the critical region near the protostar. The VANDAM survey is observing all known protostars in the Perseus Molecular Cloud. Here we present the polarization data of IRAS 4A. We find that with ~ 0.2'' (50 AU) resolution at {\lambda} = 8.1 and 10.3 mm, the inferred magnetic field is consistent with a circular morphology, in marked contrast with the hourglass morphology seen on larger scales. This morphology is consistent with frozen-in field lines that were dragged in by rotating material entering the infall region. The field morphology is reminiscent of rotating circumstellar material near the protostar. This is the first polarization detection of a protostar at these wavelengths. We conclude from our observations that the dust emission is optically thin with {\beta} ~ 1.3, suggesting that mm/cm-sized grains have grown and survived in the short lifetime of the protostar.
We present the first study of the spatial distribution of star formation in z~0.5 cluster galaxies. The analysis is based on data taken with the Wide Field Camera 3 as part of the Grism Lens-Amplified Survey from Space (GLASS). We illustrate the methodology by focusing on two clusters (MACS0717.5+3745 and MACS1423.8+2404) with different morphologies (one relaxed and one merging) and use foreground and background galaxies as field control sample. The cluster+field sample consists of 42 galaxies with stellar masses in the range 10^8-10^11 M_sun, and star formation rates in the range 1-20 M_sun/yr. Both in clusters and in the field, H{\alpha} is more extended than the rest-frame UV continuum in 60% of the cases, consistent with diffuse star formation and inside out growth. In ~20% of the cases, the H{\alpha} emission appears more extended in cluster galaxies than in the field, pointing perhaps to ionized gas being stripped and/or star formation being enhanced at large radii. The peak of the H{\alpha} emission and that of the continuum are offset by less than 1 kpc. We investigate trends with the hot gas density as traced by the X-ray emission, and with the surface mass density as inferred from gravitational lens models and find no conclusive results. The diversity of morphologies and sizes observed in H_alpha illustrates the complexity of the environmental process that regulate star formation. Upcoming analysis of the full GLASS dataset will increase our sample size by almost an order of magnitude, verifying and strengthening the inference from this initial dataset.
We analyze the mass, temperature, metal enrichment, and OVI abundance of the circumgalactic medium (CGM) around $z\sim 0.2$ galaxies of mass $10^9 M_\odot <M_\bigstar < 10^{11.5} M_\odot$ in the Illustris simulation. Among star-forming galaxies, the mass, temperature, and metallicity of the CGM increase with stellar mass, driving an increase in the OVI column density profile of $\sim 0.5$ dex with each $0.5$ dex increase in stellar mass. Observed OVI column density profiles exhibit a weaker mass dependence than predicted: the simulated OVI abundance profiles are consistent with those observed for star-forming galaxies of mass $M_\bigstar = 10^{10.5-11.5} M_\odot$, but underpredict the observed OVI abundances by $\gtrsim 0.8$ dex for lower-mass galaxies. We suggest that this discrepancy may be alleviated with additional heating of the abundant cool gas in low-mass halos, or with increased numerical resolution capturing turbulent/conductive mixing layers between CGM phases. Quenched galaxies of mass $M_\bigstar = 10^{10.5-11.5} M_\odot$ are found to have 0.3-0.8 dex lower OVI column density profiles than star-forming galaxies of the same mass, in qualitative agreement with the observed OVI abundance bimodality. This offset is driven by AGN feedback, which quenches galaxies by heating the CGM and ejecting significant amounts of gas from the halo. Finally, we find that the inclusion of the central galaxy's radiation field may enhance the photoionization of the CGM within $\sim 50$ kpc, further increasing the predicted OVI abundance around star-forming galaxies.
The cumulative emission resulting from hadronic cosmic-ray interactions in star-forming galaxies (SFGs) has been proposed as the dominant contribution to the astrophysical neutrino flux at TeV to PeV energies reported by IceCube. The same particle interactions also inevitably create gamma-ray emission that could be detectable as a component of the extragalactic gamma-ray background (EGB), now measured with the Fermi-LAT in the energy range from 0.1 to 820 GeV. New studies of the blazar flux distribution at gamma-ray energies above 50 GeV place an upper bound on the residual non-blazar component of the EGB. We show that these results are in strong tension with models that consider SFGs as the dominant source of the diffuse neutrino backgrounds.
Collisional debris around interacting and post-interacting galaxies often display condensations of gas and young stars that can potentially form gravitationally bound objects: Tidal Dwarf Galaxies (TDGs). We summarise recent results on TDGs, which are originally published in Lelli et al. (2015, A&A). We study a sample of six TDGs around three different interacting systems, using high-resolution HI observations from the Very Large Array. We find that the HI emission associated to TDGs can be described by rotating disc models. These discs, however, would have undergone less than one orbit since the time of the TDG formation, raising the question of whether they are in dynamical equilibrium. Assuming that TDGs are in dynamical equilibrium, we find that the ratio of dynamical mass to baryonic mass is consistent with one, implying that TDGs are devoid of dark matter. This is in line with the results of numerical simulations where tidal forces effectively segregate dark matter in the halo from baryonic matter in the disc, which ends up forming tidal tails and TDGs.
Early dark energy (EDE) models are a class of quintessence dark energy with a dynamically evolving scalar field which display a small but non-negligible amount of dark energy at the epoch of matter-radiation equality. Compared with a cosmological constant, the presence of dark energy at early times changes the cosmic expansion history and consequently the shape of the linear theory power spectrum and potentially other observables. We constrain the cosmological parameters in the EDE cosmology using recent measurements of the cosmic microwave background and baryon acoustic oscillations. The best-fitting models favour no EDE; here we consider extreme examples which are in mild tension with current observations in order to explore the observational consequences of a maximally allowed amount of EDE. We study the non-linear evolution of cosmic structure in EDE cosmologies using large volume N-body simulations. Many large-scale structure statistics are found to be very similar between the $\Lambda$ cold dark matter ($\Lambda$CDM) and EDE models. We find that the most promising way to distinguish EDE from $\Lambda$CDM is to measure the power spectrum on large scales, where differences of up to 15% are expected.
The Fermi Large Area Telescope (LAT) Collaboration has recently released a catalog of 360 sources detected above 50 GeV (2FHL). This catalog was obtained using 80 months of data re-processed with Pass 8, the newest event-level analysis, which significantly improves the acceptance and angular resolution of the instrument. Most of the 2FHL sources at high Galactic latitude are blazars. Using detailed Monte Carlo simulations, we measure, for the first time, the source count distribution, $dN/dS$, of extragalactic $\gamma$-ray sources at $E>50$ GeV and find that it is compatible with a Euclidean distribution down to the lowest measured source flux in the 2FHL ($\sim8\times 10^{-12}$ ph cm$^{-2}$ s$^{-1}$). We employ a one-point photon fluctuation analysis to constrain the behavior of $dN/dS$ below the source detection threshold. Overall the source count distribution is constrained over three decades in flux and found compatible with a broken power law with a break flux, $S_b$, in the range $[8 \times 10^{-12},1.5 \times 10^{-11}]$ ph cm$^{-2}$ s$^{-1}$ and power-law indices below and above the break of $\alpha_2 \in [1.60,1.75]$ and $\alpha_1 = 2.49 \pm 0.12$ respectively. Integration of $dN/dS$ shows that point sources account for at least $86^{+16}_{-14}\%$ of the total extragalactic $\gamma$-ray background. The simple form of the derived source count distribution is consistent with a single population (i.e. blazars) dominating the source counts to the minimum flux explored by this analysis. We estimate the density of sources detectable in blind surveys that will be performed in the coming years by the Cherenkov Telescope Array.
We investigate the origin of extragalactic continuum emission and its relation to the stellar population of a recently discovered peculiar z=3.344 Lyman alpha emitter. Based on an analysis of the broad-band colors and morphology we find further support for the idea that the underlying galaxy is being fed by a large-scale (L > 35 kpc) accretion stream. Archival HST images show small scale (~5 kpc) tentacular filaments converging near a hot-spot of star-formation, possibly fueled by gas falling in along the filaments. The spectral energy distribution of the tentacles is broadly compatible with either (1) non-ionizing rest-frame far-UV continuum emission from stars formed in an 60 million-year-old starburst; (2) nebular 2-photon-continuum radiation, arising from collisional excitation cooling, or (3) a recombination spectrum emitted by hydrogen fluorescing in response to ionizing radiation escaping from the galaxy. The latter possibility simultaneously accounts for the presence of asymmetric Lyman alpha emission from the large-scale gaseous filament and the nebular continuum in the smaller-scale tentacles as caused by the escape of ionizing radiation from the galaxy. Possible astrophysical explanations for the nature of the tentacles include: a galactic wind powered by the starburst; in-falling gas during cold accretion, or tails of interstellar medium dragged out of the galaxy by satellite halos that have plunged through the main halo. The possibility of detecting extragalactic 2-photon continuum emission in space-based, broad-band images suggests a tool for studying the gaseous environment of high redshift galaxies at much greater spatial detail than possible with Lyman alpha or other resonance line emission.
The "gravitational million-body problem," to model the dynamical evolution of a self-gravitating, collisional N-body system with N ~10^6 over many relaxation times, remains a major challenge in computational astrophysics. Unfortunately, current techniques to model such a system suffer from severe limitations. A direct N-body simulation with more than 10^5 particles can require months or even years to complete, while an orbit-sampling Monte Carlo approach cannot adequately treat the details of the core dynamics, particularly in the presence of many black holes. We have developed a new technique combining the precision of direct N-body codes with the speed of a Monte Carlo approach. Our Rapid And Precisely Integrated Dynamics code, the RAPID code, statistically models interactions between neighboring stars and stellar binaries while integrating directly the orbits of stars in the cluster core. This allows us to accurately simulate the dynamics of the black holes in a realistic globular cluster environment without the burdensome N^2 scaling of a full N-body integration. We compare models of idealized globular clusters created by the RAPID approach to direct N-body and Monte Carlo models. Our tests show that RAPID can reproduce the half-mass and core radii of the direct N-body models far more accurately than the Monte Carlo approach and in ~1/200th of the computing time. With this technique, it will be possible to create realistic models of Milky Way globular clusters with sufficient rapidity to explore the full parameter space of dense stellar clusters.
The photo-dissociation of H$_2$ by a nearby anisotropic source of radiation is seen as a critical component in creating an environment in which a direct collapse black hole may form. Employing radiative transfer we model the effect of multi-frequency (0.76 eV - 60 eV) radiation on a collapsing halo at high redshift. We vary both the shape of the spectrum which emits the radiation and the distance to the emitting galaxy. We use blackbody spectra with temperatures of $\rm{T = 10^4\ K}$ and $\rm{T = 10^5\ K}$ and a realistic stellar spectrum. We find that an optimal zone exists between 1 kpc and 4 kpc from the emitting galaxy. If the halo resides too close to the emitting galaxy the photo-ionising radiation creates a large HII region which effectively disrupts the collapsing halo, too far from the source and the radiation flux drops below the level of the expected background and the H$_2$ fraction remains too high. When the emitting galaxy is initially placed between 1 kpc and 2 kpc from the collapsing halo, with a spectral shape consistent with a star-forming high redshift galaxy, then a large central core forms. The mass of the central core is between 5000 and 10000 $\rm{M_{\odot}}$ at a temperature of approximately 700 K. This core is however surrounded by a reservoir of hotter gas at approximately 8000 K which leads to mass inflow rates of the order of $\sim 0.1$ $\rm{M_{\odot}}$ yr$^{-1}$. This environment has the potential to form a massive primordial star which can then lead to the formation of a direct collapse black hole.
Ultraviolet (UV) radiation is common to most planetary environments, and
could play a key role in the chemistry of molecules relevant to abiogenesis
(prebiotic chemistry). In this work, we explore the impact of UV light on
prebiotic chemistry that might occur in liquid water on the surface of a planet
with an atmosphere. We consider effects including atmospheric absorption,
attenuation by water, and stellar variability to constrain the UV input as a
function of wavelength. We conclude that the UV environment would be
characterized by broadband input, and wavelengths below 204 nm and 168 nm would
be shielded out by atmospheric CO2 and water, respectively. We compare this
broadband prebiotic UV input to the narrowband UV sources (e.g. mercury lamps)
often used in laboratory studies of prebiotic chemistry, and explore the
implications for the conclusions drawn from these experiments. We consider as
case studies the ribonucleotide synthesis pathway of Powner et al (2009) and
the sugar synthesis pathway of Ritson et al (2012). Irradiation by narrowband
UV light from a mercury lamp formed an integral component of these studies: we
quantitatively explore the impact of more realistic UV input on the conclusions
that can be drawn from these experiments. Finally, we explore the constraints
solar UV input places on the buildup of prebiotically important feedstock
gasses like CH4 and HCN. Our results demonstrate the importance of
characterizing the wavelength dependence (action spectra) of prebiotic
synthesis pathways to determine how pathways derived under laboratory
irradiation conditions will function under planetary prebiotic conditions.
Keywords: Laboratory Investigations; Origin of Life; Planetary Environments;
UV Radiation; RNA World
We present observations of four rapidly rising (t_{rise}~10d) transients with peak luminosities between those of supernovae (SNe) and superluminous SNe (M_{peak}~-20) - one discovered and followed by the Palomar Transient Factory (PTF) and three by the Supernova Legacy Survey (SNLS). The light curves resemble those of SN 2011kl, recently shown to be associated with an ultra-long-duration gamma ray burst (GRB), though no GRB was seen to accompany our SNe. The rapid rise to a luminous peak places these events in a unique part of SN phase space, challenging standard SN emission mechanisms. Spectra of the PTF event formally classify it as a Type II SN due to broad Halpha emission, but an unusual absorption feature, which can be interpreted as either high velocity Halpha (though deeper than in previously known cases) or Si II (as seen in Type Ia SNe), is also observed. We find that existing models of white dwarf detonations, CSM interaction, shock breakout in a wind (or steeper CSM) and magnetar spindown can not readily explain the observations. We look into the intriguing possibility of a "Type 1.5 SN" scenario for our events, but can not confirm nor reject this interpretation. More detailed models for these kinds of transients and more constraining observations of future such events should help better determine their nature.
The angular dependence of emission in gamma-ray bursts (GRB) is of fundamental importance in understanding the underlying physical mechanisms, as well as in multimessenger search efforts. We examine the prospects of using reconstructed GRB jet opening angles and off-axis observer angles in determining the jet structure. We show that the reconstructed angles by Ryan et al. (2015) are inconsistent with uniform jet structure. We further calculate the number of GRBs with accurately reconstructed opening and observer angles necessary to differentiate between some phenomenological non-uniform structures.
The complex interplay of processes at the Galactic Center is at the heart of numerous past, present, and (likely) future mysteries. We aim at a more complete understanding of how spectra extending to >10 TeV result. We first construct a simplified model to account for the peculiar energy and angular dependence of the intense central parsec photon field. This allows for calculating anisotropic inverse Compton scattering and mapping gamma-ray extinction due to gamma gamma -> e^+ e^- attenuation. Coupling these with a method for evolving electron spectra, we examine several clear and present excesses, including the diffuse hard X-rays seen by NuSTAR and GeV gamma rays by Fermi. We address further applications to cosmic rays, dark matter, neutrinos, and gamma rays from the Center and beyond.
A large number of intermediate-age (~1-2-Gyr old) globular clusters (GCs) in the Large and the Small Magellanic Cloud (MC) exhibit either bimodal or extended main-sequence (MS) turn off and dual red clump. Moreover, recent papers have shown that the MS of the young clusters NGC1844 and NGC1856 is either broadened or split. These features of the color-magnitude diagram (CMD) are not consistent with a single isochrone and suggest that star clusters in MCs have experienced a prolonged star formation, in close analogy with Milky-Way GCs with multiple stellar populations. As an alternative, stellar rotation or interacting binaries can be responsible of the CMD morphology. In the following I will summarize the observational scenario and provide constraints on the nature of the complex CMD of young and intermediate-age MC clusters from our ongoing photometric survey with the Hubble Space Telescope.
This paper discusses a new approach for determining the calibration parameters of independently-actuated optical fibers in multi-object astronomical fiber positioning systems. This work comes from the development of a new type of piezoelectric motor intended to enhance the 'tilting spine' fiber positioning technology originally created by the Australian Astronomical Observatory. Testing has shown that the motor's performance can vary depending on the fiber's location within its accessible field, meaning that an individual fiber is difficult calibrate with a one-time routine. Better performance has resulted from constantly updating calibration parameters based on the observed movements of the fiber during normal closed-loop positioning. Over time, location-specific historical data is amassed that can be used to better predict the results of a future fiber movement. This is similar to a technique previously proposed by the Australian Astronomical Observatory, but with the addition of location-specific learning. Results from a prototype system are presented, showing a significant reduction in overall positioning error when using this new approach.
Based on a combined analysis of SDSS imaging and CALIFA integral field spectroscopy data, we report on the detection of faint (24 < {\mu}$_r$ mag/arcsec$^2$ < 26) star-forming spiral-arm-like features in the periphery of three nearby early-type galaxies (ETGs). These features are of considerable interest because they document the still ongoing inside-out growth of some local ETGs and may add valuable observational insight into the origin and evolution of spiral structure in triaxial stellar systems. A characteristic property of the nebular component in the studied ETGs, classified i+, is a two-radial-zone structure, with the inner zone that displays faint (EW(H\alpha)$\simeq$1{\AA}) low-ionization nuclear emission-line region (LINER) properties, and the outer one (3{\AA}<EW(H\alpha)<~20{\AA}) HII-region characteristics. This spatial segregation of nebular emission in two physically distinct concentric zones calls for an examination of aperture effects in studies of type i+ ETGs with single-fiber spectroscopic data.
Binary neutron star mergers are strong gravitational wave (GW) sources and the leading candidates to interpret short duration gamma-ray bursts (SGRBs). Under the assumptions that SGRBs are produced by double neutron star mergers, we use the statistical observational properties of {\em Swift} SGRBs and the mass distribution of Galactic double neutron star systems to place constraints on the neutron star equation of state (EoS) and the properties of the post-merger product. We show that current observations already put following tight constraints: 1) A neutron star EoS with a maximum mass close to a parameterization of $M_{\rm max} = 2.37\,M_\odot (1+1.58\times10^{-10} P^{-2.84})$ is favored; 2) The fractions for the several outcomes of NS-NS mergers are as follows: $\sim40\%$ prompt BHs, $\sim30\%$ supra-massive NSs that collapse to BHs in a range of delay time scales, and $\sim30\%$ stable NSs that never collapse; 3) The initial spin of the newly born supra-massive NSs should be near the breakup limit ($P_i\sim1 {\rm ms}$), which is consistent with the merger scenario; 4) The surface magnetic field of the merger products is typically $\sim 10^{15}$ G; 5) The ellipticity of the supra-massive NSs is $\epsilon \sim (0.004 - 0.007)$, so that strong GW radiation is released post the merger; 6) Even though the initial spin energy of the merger product is similar, the final energy output of the merger product that goes into the electromagnetic channel varies in a wide range from several $10^{49}$ erg to several $10^{52}$ erg, since a good fraction of spin energy is either released in the form of GW or falls into the black hole as the supra-massive NS collapses.
We present dust column densities and dust temperatures for $\sim3000$ young high-mass molecular clumps from the Millimetre Astronomy Legacy Team 90 GHz (MALT90) survey, derived from adjusting single temperature dust emission models to the far-infrared intensity maps measured between 160 and 870 \micron\ from the Herschel/Hi-Gal and APEX/ATLASGAL surveys. We discuss the methodology employed in analyzing the data, calculating physical parameters, and estimating their uncertainties. The population average dust temperature of the clumps are: $16.8\pm0.2$ K for the clumps that do not exhibit mid-infrared signatures of star formation (Quiescent clumps), $18.6\pm0.2$ K for the clumps that display mid-infrared signatures of ongoing star formation but have not yet developed an HII region (Protostellar clumps), and $23.7\pm0.2$ and $28.1\pm0.3$ K for clumps associated with HII and photo-dissociation regions, respectively. These four groups exhibit large overlaps in their temperature distributions, with dispersions ranging between 4 and 6 K. The median of the peak column densities of the Protostellar clump population is $0.20\pm0.02$ gr cm$^{-2}$, which is about 50% higher compared to the median of the peak column densities associated with clumps in the other evolutionary stages. We compare the dust temperatures and column densities measured toward the center of the clumps with the mean values of each clump. We find that in the Quiescent clumps the dust temperature increases toward the outer regions and that they are associated with the shallowest column density profiles. In contrast, molecular clumps in the Protostellar or HII region phase have dust temperature gradients more consistent with internal heating and are associated with steeper column density profiles compared with the Quiescent clumps.
Boulders are ubiquitously found on the surfaces of small rocky bodies in the inner solar system and their spatial and size distributions give insight into the geological evolution and collisional history of the parent bodies. Using images acquired by the Chang'e-2 spacecraft, more than 200 boulders have been identified over the imaged area of the near-Earth asteroid Toutatis. The cumulative boulder size frequency distribution (SFD) shows a steep slope of -4.4 $\pm$ 0.1, which is indicative of a high degree of fragmentation. Similar to Itokawa, Toutatis probably has a rubble-pile structure, as most boulders on its surface cannot solely be explained by impact cratering. The significantly steeper slope for Toutatis' boulder SFD compared to Itokawa may imply a different preservation state or diverse formation scenarios. In addition, the cumulative crater SFD has been used to estimate a surface crater retention age of approximately 1.6 $\pm$ 0.3 Gyr.
Motivated by the previously reported high orbital decay rate of the planet WASP-43b, eight newly transit light curves are obtained and presented. Together with other data in literature, we perform a self-consistent timing analysis with data covering a timescale of 1849 epochs. The results give an orbital decay rate dP/dt = -0.02890795\pm 0.00772547 sec/year, which is one order smaller than previous values. This slow decay rate corresponds to a normally assumed theoretical value of stellar tidal dissipation factor. In addition, through the frequency analysis, the transit timing variations presented here are unlikely to be periodic, but could be signals of a slow orbital decay.
Because most massive stars have been or will be affected by a companion during the course of their evolution, we cannot afford to neglect binaries when discussing the progenitors of supernovae and GRBs. Analyzing linear polarization in the emission lines of close binary systems allows us to probe the structures of these systems' winds and mass flows, making it possible to map the complex morphologies of the mass loss and mass transfer structures that shape their subsequent evolution. In Wolf-Rayet (WR) binaries, line polarization variations with orbital phase distinguish polarimetric signatures arising from lines that scatter near the stars from those that scatter far from the orbital plane. These far-scattering lines may form the basis for a "binary line-effect method" of identifying rapidly rotating WR stars (and hence GRB progenitor candidates) in binary systems.
We assess the effectiveness of the Jeans-Anisotropic-MGE (JAM) technique with a state-of-the-art cosmological hydrodynamic simulation, the Illustris project. We perform JAM modelling on 1413 simulated galaxies with stellar mass M^* > 10^{10}M_{sun}, and construct an axisymmetric dynamical model for each galaxy. Combined with a Markov Chain Monte Carlo (MCMC) simulation, we recover the projected root-mean-square velocity (V_rms) field of the stellar component, and investigate constraints on the stellar mass-to-light ratio, M^*/L, and the fraction of dark matter f_{DM} within 2.5 effective radii (R_e). We find that the enclosed total mass within 2.5 R_e is well constrained to within 10%. However, there is a degeneracy between the dark matter and stellar components with correspondingly larger individual errors. The 1 sigma scatter in the recovered M^*/L is 30-40% of the true value. The accuracy of the recovery of M^*/L depends on the triaxial shape of a galaxy. There is no significant bias for oblate galaxies, while for prolate galaxies the JAM-recovered stellar mass is on average 18% higher than the input values. We also find that higher image resolutions alleviate the dark matter and stellar mass degeneracy and yield systematically better parameter recovery.
The IceCube collaboration reports a detection of extra-terrestrial neutrinos. The isotropy and flavor content of the signal, and the coincidence, within current uncertainties, of the 50 TeV to 2 PeV flux and the spectrum with the Waxman-Bahcall bound, suggest a cosmological origin of the neutrinos, related to the sources of ultra-high energy, $>10^{10}$ GeV, cosmic-rays (UHECR). The most natural explanation of the UHECR and neutrino signals is that both are produced by the same population of cosmological sources, producing CRs (likely protons) at a similar rate, $E^2d\dot{n}/dE\propto E^{0}$, over the [$1$ PeV,$10^{11}$ GeV] energy range, and residing in "calorimetric" environments, like galaxies with high star formation rate, in which $E/Z<100$ PeV CRs lose much of their energy to pion production. A tenfold increase in the effective mass of the detector at $\gtrsim100$ TeV is required in order to significantly improve the accuracy of current measurements, to enable the detection of a few bright nearby starburst "calorimeters", and to open the possibility of identifying the CR sources embedded within the calorimeters, by associating neutrinos with photons accompanying transient events responsible for their generation. Source identification and a large neutrino sample may enable one to use astrophysical neutrinos to constrain new physics models.
We use a combination of data acquired with the Advanced Camera for Survey (ACS) on board the Hubble Space Telescope and the Large Binocular Camera (LBC-blue) mounted on the Large Binocular Telescope, to sample the main sequence stars of the globular cluster NGC~5466 in the mass range $0.3<M/M_\odot<0.8$. We derive the cluster's Luminosity Function in several radial regions, from the center of the cluster out to the tidal radius. After corrections for incompleteness and field-contamination, this has been compared to theoretical Luminosity Functions, obtained by multiplying a simple power law Mass Function in the form dN/dm$ \propto m^{\alpha}$ by the derivative of the mass-luminosity relationship of the best-fit isochrone. We find that $\alpha$ varies from -0.6 in the core region to -1.9 in the outer region. This fact allows us to observationally prove that the stars in NGC 5466 have experienced the effects of mass segregation. We compare the radial variation of $\alpha$ from the center out to 5 core radii (r$_c$) in NGC 5466 and the globular cluster M10, finding that the gradient of $\alpha$ in the first 5r$_c$ is more than a factor of 2 shallower in NGC 5466 than in M10, in line with the differences in the clusters' relaxation timescales. NGC 5466 is dynamically younger than M10, with two-body relaxation processes only recently starting to shape the distribution of main sequence stars. This result fully agrees with the conclusion obtained in our previous works on the radial distribution of Blue Straggler Stars, further confirming that this can be used as an efficient clock to measure the dynamical age of stellar systems.
It is widely accepted that stars do not form in isolation but result from the fragmentation of molecular clouds, which in turn leads to star cluster formation. Over time, clusters dissolve or are destroyed by interactions with molecular clouds or tidal stripping, and their members become part of the general field population. Star clusters are thus among the basic building blocks of galaxies. In turn, star cluster populations, from young associations and open clusters to old globulars, are powerful tracers of the formation, assembly, and evolutionary history of their parent galaxies. Although their importance had been recognised for decades, major progress in this area has only become possible in recent years, both for Galactic and extragalactic cluster populations. Star clusters are the observational foundation for stellar astrophysics and evolution, provide essential tracers of galactic structure, and are unique stellar dynamical environments. Star formation, stellar structure, stellar evolution, and stellar nucleosynthesis continue to benefit and improve tremendously from the study of these systems. Additionally, fundamental quantities such as the initial mass function can be successfully derived from modelling either the H-R diagrams or the integrated velocity structures of, respectively, resolved and unresolved clusters and cluster populations. Star cluster studies thus span the fields of Galactic and extragalactic astrophysics, while heavily affecting our detailed understanding of the process of star formation in dense environments.This report highlights science results of the last decade in the major fields covered by IAU Commission 37: Star clusters and associations.
Ground-based observations at terahertz (THz) frequencies are a newly explorable area of astronomy for the next ten years. We discuss science cases for a first-generation 10-m class THz telescope, focusing on the Greenland Telescope as an example of such a facility. We propose science cases and provide quantitative estimates for each case. The largest advantage of ground-based THz telescopes is their higher angular resolution (~ 4 arcsec for a 10-m dish), as compared to space or airborne THz telescopes. Thus, high-resolution mapping is an important scientific argument. In particular, we can isolate zones of interest for Galactic and extragalactic star-forming regions. The THz windows are suitable for observations of high-excitation CO lines and [N II] 205 um lines, which are scientifically relevant tracers of star formation and stellar feedback. Those lines are the brightest lines in the THz windows, so that they are suitable for the initiation of ground-based THz observations. THz polarization of star-forming regions can also be explored since it traces the dust population contributing to the THz spectral peak. For survey-type observations, we focus on ``sub-THz'' extragalactic surveys, whose uniqueness is to detect galaxies at redshifts z ~ 1--2, where the dust emission per comoving volume is the largest in the history of the Universe. Finally we explore possibilities of flexible time scheduling, which enables us to monitor active galactic nuclei, and to target gamma-ray burst afterglows. For these objects, THz and submillimeter wavelength ranges have not yet been explored.
We employ CaII K and NaI D interstellar absorption-line spectroscopy of
early-type stars in the Large and Small Magellanic Clouds to investigate the
large- and small-scale structure in foreground Intermediate and High Velocity
Clouds (I/HVCs). These data include FLAMES-GIRAFFE CaII K observations of 403
stars in four open clusters, plus FEROS or UVES spectra of 156 stars in the LMC
and SMC. The FLAMES observations are amongst the most extensive probes to date
of CaII structures on 20 arcsec scales
From the FLAMES data within a 0.5 degree field-of-view, the CaII K equivalent
width in the I/HVC components towards three clusters varies by factors of >10.
There are no detections of molecular gas in absorption at intermediate or high
velocities, although molecular absorption is present at LMC and Galactic
velocities towards some sightlines. The sightlines show variations in EW
exceeding a factor 7 in CH+ towards NGC 1761 over scales of less than 10
arcminutes.
The FEROS/UVES data show CaII K I/HVC absorption in $\sim$60 per cent of
sightlines. No NaI D is found at non-Magellanic HVC velocities aside from a
tentative detection towards the star LHA 120-S 93. The range in the CaII/NaI
ratio in I/HVCs is from -0.45 to +1.5 dex, similar to previous measurements for
I/HVCs.
In ten sightlines we find CaII/OI ratios in I/HVC gas ranging from 0.2 to 1.5
dex below the solar value, indicating either dust or ionisation effects. In
nine sightlines I/HVC gas is detected in both HI and CaII, and shows similar
CaII/HI ratios to typical I/HVCs, and similar velocities, implying that in
these sightlines the two elements form part of the same structure.
Debris disks are usually thought to be gas-poor, the gas being dissipated by accretion or evaporation during the protoplanetary phase. HD141569A is a 5 Myr old star harboring a famous debris disk, with multiple rings and spiral features. We present here the first PdBI maps of the 12CO(2-1), 13CO(2-1) gas and dust emission at 1.3 mm in this disk. The analysis reveals there is still a large amount of (primordial) gas extending out to 250 au, i. e. inside the rings observed in scattered light. HD141569A is thus a hybrid disk with a huge debris component, where dust has evolved and is produced by collisions, with a large remnant reservoir of gas.
We discuss our most recent findings on the diffuse X-ray emission from Wolf-Rayet (WR) nebulae. The best-quality X-ray observations of these objects are those performed by XMM-Newton and Chandra towards S308, NGC2359, and NGC6888. Even though these three WR nebulae might have different formation scenarios, they all share similar characteristics: i) the main plasma temperatures of the X-ray-emitting gas is found to be $T$=[1-2]$\times$10$^{6}$ K, ii) the diffuse X-ray emission is confined inside the [O III] shell, and iii) their X-ray luminosities and electron densities in the 0.3-2.0~keV energy range are $L_\mathrm{X}\approx$10$^{33}$-10$^{34}$~erg~s$^{-1}$ and $n_\mathrm{e}\approx$0.1-1~cm$^{-3}$, respectively. These properties and the nebular-like abundances of the hot gas suggest mixing and/or thermal conduction is taking an important role reducing the temperature of the hot bubble.
Extinction remains one of the most reliable methods of measuring column density of nearby Galactic interstellar clouds. The current and ongoing near-infrared surveys enable the mapping of extinction over large sky areas. We produce allsky extinction maps using the 2MASS near-infrared survey. We use the NICER and NICEST methods to convert the near-infrared colour excesses to extinction estimates. The results are presented in Healpix format at the resolutions of 3.0, 4.5, and 12.0 arcmin. The main results of this study are the calculated J-band extinction maps. The comparison with earlier large-scale extinction mappings shows good correspondence but also demonstrates the presence of resolution-dependent bias. A large fraction of the bias can be corrected by using the NICEST method. For individual regions, best extinction estimates are obtained by careful analysis of the local stellar population and the use of the highest resolution afforded by the stellar density. However, the uniform allsky maps should still be useful for many global studies and as the first step into the investigation of individual clouds.
Several methods exist to convert near-infrared (NIR) stellar observations into extinction maps. We present a new method based on NIR multiband observations. The method uses a discretised version of the distribution of intrinsic stellar colours. A number of variations of the basic method are tested, and the results are compared to NICER calculations. When photometric errors are large, the results are close to those of NICER method but some advantages can be seen when the distribution of intrinsic colours cannot be described well with a single covariance matrix. A priori information about relative column density variations at sub-beam scales can result in a significant increase in accuracy. The results may be further improved by considering the magnitude dependence of the intrinsic colours. Thus, the new methods are useful mostly when photometric errors are small, the distribution of intrinsic colours is well known, or one has prior knowledge of the small-scale structures.
The deuterium fractionation of gas-phase molecules in hot cores is believed to reflect the composition of interstellar ices. The deuteration of methanol is a major puzzle, however, because the isotopologue ratio [CH2DOH]/[CH3OD], which is predicted to be equal to 3 by standard grain chemistry models, is much larger (~20) in low-mass hot corinos and significantly lower (~1) in high-mass hot cores. This dichotomy in methanol deuteration between low-mass and massive protostars is currently not understood. In this study, we report a simplified rate equation model of the deuterium chemistry occurring in the icy mantles of interstellar grains. We apply this model to the chemistry of hot corinos and hot cores, with IRAS 16293-2422 and the Orion~KL Compact Ridge as prototypes, respectively. The chemistry is based on a statistical initial deuteration at low temperature followed by a warm-up phase during which thermal hydrogen/deuterium (H/D) exchanges occur between water and methanol. The exchange kinetics is incorporated using laboratory data. The [CH2DOH]/[CH3OD] ratio is found to scale inversely with the D/H ratio of water, owing to the H/D exchange equilibrium between the hydroxyl (-OH) functional groups of methanol and water. Our model is able to reproduce the observed [CH2DOH]/[CH3OD] ratios provided that the primitive fractionation of water ice [HDO]/[H2O] is ~ 2% in IRAS 16293-2422 and ~0.6% in Orion~KL. We conclude that the molecular D/H ratios measured in hot cores may not be representative of the original mantles because molecules with exchangeable deuterium atoms can equilibrate with water ice during the warm-up phase.
Uncertainties in the thermonuclear rates of the $^{15}$O($\alpha,\gamma$)$^{19}$Ne and $^{18}$F($p,\alpha$)$^{15}$O reactions affect model predictions of light curves from type I X-ray bursts and the amount of the observable radioisotope $^{18}$F produced in classical novae, respectively. To address these uncertainties, we have studied the nuclear structure of $^{19}$Ne over $E_{x} = 4.0 - 5.1$ MeV and $6.1 - 7.3$ MeV using the $^{19}$F($^{3}$He,t)$^{19}$Ne reaction. We find the $J^{\pi}$ values of the 4.14 and 4.20 MeV levels to be consistent with $9/2^{-}$ and $7/2^{-}$ respectively, in contrast to previous assumptions. We confirm the recently observed triplet of states around 6.4 MeV, and find evidence that the state at 6.29 MeV, just below the proton threshold, is either broad or a doublet. Our data also suggest that predicted but yet unobserved levels may exist near the 6.86 MeV state. Higher resolution experiments are urgently needed to further clarify the structure of $^{19}$Ne around the proton threshold before a reliable $^{18}$F($p,\alpha$)$^{15}$O rate for nova models can be determined.
We present near-infrared (NIR) $H+K$-band longslit spectra of eleven galaxies
which are obtained with SOFI at the NTT (ESO). The galaxies are chosen from the
low-luminosity type-1 quasi-stellar object (LLQSO) sample which comprises the
99 closest ($z\leq 0.06$) QSOs from the Hamburg/ESO survey for bright UV-excess
QSOs. These objects are ideal targets to study the gap between local Seyfert
galaxies and high-redshift quasars, since they show much stronger AGN activity
compared to local objects but are still close enough for a detailed structural
analysis.
We fit hydrogen recombination, molecular hydrogen, and [FeII] lines after
carefully subtracting the continuum emission. From the broad Pa$\alpha$
components, we estimate black hole masses and enlarge the sample of LLQSOs that
show a deviation from the $M_\mathrm{BH}-L_\mathrm{bulge}$ relations of
inactive galaxies from 12 to 16 objects.
All objects show emission from hot dust ($T\sim 1200\,\mathrm{K}$) as well as
stellar contribution. However, the particular fractions vary a lot between the
objects. More than half of the objects show H$_2$ emission lines that are
indicating a large reservoir of molecular gas which is needed to feed the AGN
and star formation.
In the NIR diagnostic diagram all objects lie in the location of AGN
dominated objects. However, most of the objects show indications of star
formation activity, suggesting that their offset location with respect to
$M_\mathrm{BH}-L_\mathrm{bulge}$ relations of inactive galaxies may be a
consequence of overluminous bulges.
We report on the first detection of X-ray dust scattered rings from the Galactic low mass X-ray binary V404 Cyg. The observation of the system with Swift/XRT on June 30 2015 revealed the presence of five concentric ring-like structures centred at the position of V404 Cyg. Follow-up Swift/XRT observations allowed a time-dependent study of the X-ray rings. Assuming that these are the result of small-angle, single X-ray scattering by dust grains along the line of sight, we find that their angular size scales as $\theta \propto\sqrt{t}$ in agreement with theoretical predictions. The dust grains are concentrated in five dust layers located at about 2.12, 2.05, 1.63, 1.50 and 1.18 kpc from the observer. These coincide roughly with locations of enhanced extinction as determined by infrared photometry. Assuming that the grain size distribution is described by a generalized Mathis-Rumpl-Nordsieck model, we find that the power-law index of the most distant cloud is $q\sim 4.4$, while $q \sim 3.5-3.7$ in all other clouds. We constrain at a $3\sigma$ level the maximum grain size of the intermediate dust layers in the range $0.16-0.20\,\mu$m and set a lower limit of $\sim 0.2\,\mu$m in the other clouds. Hints of an exponential cutoff at the angular intensity profile of the outermost X-ray ring suggest that the smallest grains have sizes $0.01 \mu{\rm m}\le \alpha_{\min} \lesssim 0.03\,\mu$m. Based on the relative ratios of dust column densities we find the highest dust concentration at $\sim 1.6$ kpc. Our results indicate a gradient in the dust properties within 1 kpc from V404 Cyg.
Chirality of neutrinos modifies the conventional kinetic theory and hydrodynamics, and leads to unusual chiral transport related to quantum anomalies in field theory. We argue that these corrections lead to new phenomenological consequences for hot and dense neutrino gases, especially in core-collapse supernovae. We find that the neutrino density can be converted to the fluid helicity through the chiral vortical effect. This fluid helicity effectively acts as a chiral chemical potential for other charged particles via the momentum exchange with neutrinos, and it induces a "helical plasma instability" that generates a strong helical magnetic field. This provides a new mechanism for converting the gravitational energy released by the core collapse to the electromagnetic energy, and potentially explains the origin of magnetars. The other possible applications of the neutrino chiral transport theory are also discussed.
We present newly derived stellar parameters and the detailed abundances of 19 elements of seven stars with small planets discovered by NASA's Kepler Mission. Each star save one has at least one planet with a radius <= 1.6 R_Earth, suggesting a primarily rocky composition. The stellar parameters and abundances are derived from high signal-to-noise ratio, high-resolution echelle spectroscopy obtained with the 10-m Keck I telescope and HIRES spectrometer using standard spectroscopic techniques. The metallicities of the seven stars range from -0.32 dex to +0.13 dex, with an average metallicity that is subsolar, supporting previous suggestions that, unlike Jupiter-type giant planets, small planets do not form preferentially around metal-rich stars. The abundances of elements other than iron are in line with a population of Galactic disk stars, and despite our modest sample size, we find hints that the compositions of stars with small planets are similar to stars without known planets and with Neptune-size planets, but not to those of stars with giant planets. This suggests that the formation of small planets does not require exceptional host-star compositions and that small planets may be ubiquitous in the Galaxy. We compare our derived abundances (which have typical uncertainties of <= 0.04 dex) to the condensation temperature of the elements; a correlation between the two has been suggested as a possible signature of rocky planet formation. None of the stars demonstrate the putative rocky planet signature, despite at least three of the stars having rocky planets estimated to contain enough refractory material to produce the signature, if real. More detailed abundance analyses of stars known to host small planets are needed to verify our results and place ever more stringent constraints on planet formation models.
Intensity scintillations of cosmic radio sources are used to study astrophysical plasmas like the ionosphere, the solar wind, and the interstellar medium. Normally these observations are relatively narrow band. With Low Frequency Array (LOFAR) technology at the Kilpisj\"arvi Atmospheric Imaging Receiver Array (KAIRA) station in northern Finland we have observed scintillations over a 3 octave bandwidth. ``Parabolic arcs'', which were discovered in interstellar scintillations of pulsars, can provide precise estimates of the distance and velocity of the scattering plasma. Here we report the first observations of such arcs in the ionosphere and the first broad-band observations of arcs anywhere, raising hopes that study of the phenomenon may similarly improve the analysis of ionospheric scintillations. These observations were made of the strong natural radio source Cygnus-A and covered the entire 30-250\,MHz band of KAIRA. Well-defined parabolic arcs were seen early in the observations, before transit, and disappeared after transit although scintillations continued to be obvious during the entire observation. We show that this can be attributed to the structure of Cygnus-A. Initial results from modeling these scintillation arcs are consistent with simultaneous ionospheric soundings taken with other instruments, and indicate that scattering is most likely to be associated more with the topside ionosphere than the F-region peak altitude. Further modeling and possible extension to interferometric observations, using international LOFAR stations, are discussed.
We present a new general relativistic magnetohydrodynamics (GRMHD) code integrated into the Athena++ framework. Improving upon the techniques used in most GRMHD codes, ours allows the use of advanced, less diffusive Riemann solvers, in particular HLLC and HLLD. We also employ a staggered-mesh constrained transport algorithm suited for curvilinear coordinate systems in order to maintain the divergence-free constraint of the magnetic field. Our code is designed to work with arbitrary stationary spacetimes in one, two, or three dimensions, and we demonstrate its reliability in a number of tests. We also report on its promising performance and scalability.
We present a method for studying the secular gravitational dynamics of hierarchical multiple systems consisting of nested binaries, which is valid for an arbitrary number of bodies and arbitrary hierarchical structure. We derive the Hamiltonian of the system and expand it in terms of the -- assumed to be -- small ratios $x_i$ of binary separations. At the lowest nontrivial expansion order (quadrupole order, second order in $x_i$), the Hamiltonian consists of terms which, individually, depend on binary pairs. At higher orders, in addition to terms depending on binary pairs, we also find terms which, individually, depend on more than two binaries. In general, at order $n$ in $x_i$, individual terms depend on at most $n-1$ binaries. We explicitly derive the Hamiltonian including all terms up and including third order in $x_i$ (octupole order), and including the binary pairwise terms up and including fifth order in $x_i$. These terms are orbit averaged, and we present a new algorithm for efficiently solving the equations of motion. This algorithm is highly suitable for studying the secular evolution of hierarchical systems with complex hierarchies, making long-term integrations of such systems feasible for the first time. We show that accurate results are obtained for multiplanet systems with semimajor axis ratios as large as $\approx 0.4$, provided that high-order terms are included. In addition to multiplanet systems with a single star, we apply our results to multistar systems with multiple planets.
The DEAP-3600 experiment uses 3.6 tons of liquid argon for a sensitive dark matter search, with a sensitivity to the spin-independent WIMP-nucleon cross-section of $10^{-46}$ cm$^2$ at 100 GeV WIMP mass. This high sensitivity is achievable due to the large target mass and the very low backgrounds in the spherical acrylic detector design as well as at the unique SNOLAB facility in Sudbury, Canada. Pulse shape discrimination is used to reject electromagnetic backgrounds from the WIMP induced nuclear recoil signal. We started taking commissioning data in early 2015 with vacuum and later gas inside the detector. Argon fill is expected in winter 2015. An overview and status of the DEAP-3600 experiment are presented in this paper, with an emphasis on control and mitigation of detector backgrounds.
From iodine-plutonium-xenon isotope systematics, we re-evaluate time constraints on the early evolution of the Earth-atmosphere system and, by inference, on the Moon-forming event. Two extinct radioactivites (129I, T1/2 = 15.6 Ma, and 244Pu, T1/2 = 80 Ma) have produced radiogenic 129Xe and fissiogenic 131-136Xe, respectively, within the Earth, which related isotope fingerprints are seen in the compositions of mantle and atmospheric Xe. Recent studies of Archean rocks suggest that xenon atoms have been lost from the Earth's atmosphere and isotopically fractionated during long periods of geological time, until at least the end of the Archean eon. Here we build a model that takes into account these results. Correction for Xe loss permits to compute new closure ages for the Earth's atmosphere that are in agreement with those computed for mantle Xe. The minimum Xe formation interval for the Earth- atmosphere is 40 (-10+20) Ma after start of solar system formation, which may also date the Moon-forming impact.
We conduct a survey of low surface brightness (LSB) satellite galaxies around the Local Volume massive spirals using long exposures with small amateur telescopes. We identified 27 low and very low surface brightness objects around the galaxies NGC,672, 891, 1156, 2683, 3344, 4258, 4618, 4631, and 5457 situated within 10 Mpc from us, and found nothing new around NGC,2903, 3239, 4214, and 5585. Assuming that the dwarf candidates are the satellites of the neighboring luminous galaxies, their absolute magnitudes are in the range of -8.6 > M_B > -13.3, their effective diameters are 0.4-4.7 kpc, and the average surface brightness is 26.1 mag/sq arcsec. The mean linear projected separation of the satellite candidates from the host galaxies is 73 kpc. Our spectroscopic observations of two LSB dwarfs with the Russian 6-meter telescope confirm their physical connection to the host galaxies NGC,891 and NGC,2683.
Rotation is a directly-observable stellar property, and drives magnetic field generation and activity through a magnetic dynamo. Main sequence stars with masses below approximately 0.35Msun (mid-to-late M dwarfs) are fully-convective, and are expected to have a different type of dynamo mechanism than solar-type stars. Measurements of their rotation rates provide insights into these mechanisms, but few rotation periods are available for these stars at field ages. Using photometry from the MEarth transit survey, we measure rotation periods for 391 nearby, mid-to-late M dwarfs in the Northern hemisphere, finding periods from 0.1 to 150 days. The typical detected rotator has stable, sinusoidal photometric modulations at a semi-amplitude of 0.5 to 1%. We find no period-amplitude relation for stars below 0.25Msun and an anti-correlation between period and amplitude for higher-mass M dwarfs. We highlight the existence of older, slowly-rotating stars without H{\alpha} emission that nevertheless have strong photometric variability. The Galactic kinematics of our sample is consistent with the local population of G and K dwarfs, and rotators have metallicities characteristic of the Solar Neighborhood. We use the W space velocities and established age-velocity relations to estimate that stars with P<10 days are on average <2 Gyrs, and that those with P>70 days are about 5 Gyrs. The period distribution is mass dependent: as the mass decreases, the slowest rotators at a given mass have longer periods, and the fastest rotators have shorter periods. We find a lack of stars with intermediate rotation periods. [Abridged]
Knowledge of abundance ratios as functions of metallicity can lead to insights on the origin and evolution of our Galaxy and its stellar populations. We aim to trace the chemical evolution of the neutron-capture elements Sr, Zr, La, Ce, Nd, Sm, and Eu in the Milky Way stellar disk to constrain the formation sites of these elements as well as to probe the evolution of the Galactic thin and thick disks. Using spectra of high resolution and high signal-to-noise we determine Sr, Zr, La, Ce, Nd, Sm, and Eu abundances for a sample of 714 F and G dwarf stars in the Solar neighbourhood. We present abundance results for Sr, Zr, La, Ce, Nd, Sm and Eu. We find that Nd, Sm, and Eu show trends similar to what is observed for the alpha-elements when compared to [Fe/H]. [Sr/Fe] and [Zr/Fe] show decreasing abundance ratios for increasing metallicity, reaching sub-solar values at super-solar metallicities. [La/Fe] and [Ce/Fe] do not show any clear trend with metallicity. The rapid neutron-capture process is active early in the Galaxy, mainly in type II supernovae from stars in the mass range 8-10 M_sun. Eu is almost completely produced by r-process but Nd and Sm show similar trends to Eu even if their s-process component is higher. Sr and Zr show significant enrichment at low metallicity that requires extra r-process production, that probably is different from the classical r-process. Finally, La and Ce are mainly produced via s-process from AGB stars in mass range 2-4 M_sun. The trend of [X/Fe] with age found could be explained by considering that the decrease in [X/Fe] for the thick disk stars can be due to the decrease of type II supernovae with time meaning a reduced enrichment of r-process elements in the interstellar medium. In the thin disk the trends are flatter that probably is due to that the main production from s-process is balanced by Fe production from type Ia supernovae.
We derive the CO luminosity function (LF) for different rotational transitions (i.e. (1-0), (3-2), (5-4)) starting from the Herschel LF by Gruppioni et al. and using appropriate $L'_{\rm CO} - L_{\rm IR}$ conversions for different galaxy classes. Our predicted LFs fit the data so far available at $z\approx0$ and $2$. We compare our results with those obtained by semi-analytical models (SAMs): while we find a good agreement over the whole range of luminosities at $z\approx0$, at $z\approx1$ and $z\approx2$ the tension between our LFs and SAMs in the faint and bright ends increases. We finally discuss the contribution of luminous AGN ($L_{X}>10^{44}\,\rm{erg\,s^{-1}}$) to the bright end of the CO LF concluding that they are too rare to reproduce the actual CO luminosity function at $z\approx2$.
Recent Cosmic Microwave Background (CMB) temperature and polarization anisotropy measurements from the Planck mission have significantly improved previous constraints on the neutrino masses as well as the bounds on extended models with massless or massive sterile neutrino states. However, due to parameter degeneracies, additional low redshift priors are mandatory in order to sharpen the CMB neutrino bounds. We explore here the role of different priors on low redshift quantities, such as the Hubble constant, the cluster mass bias, and the reionization optical depth $\tau$. Concerning current priors on the Hubble constant and the cluster mass bias, the bounds on the neutrino parameters may differ appreciably depending on the choices adopted in the analyses. With regard to future improvements in the priors on the reionization optical depth, a value of $\tau=0.05\pm 0.01$, motivated by astrophysical estimates of the reionization redshift, would lead to $\sum m_\nu<0.0993$~eV at $95\%$~CL, thereby opening the window to unravel the neutrino mass hierarchy with existing cosmological probes.
Abundance studies of solar-type stars revealed a small fraction of objects with extreme depletion of beryllium. We investigate the possible link between the beryllium depletion and the presence of companions. The classical methods (radial velocity, astrometry, imaging) used to search for binary companions were exploited. We also performed a chemical analysis to identify binaries by the alteration in abundances that is produced by the accretion of material lost by a former evolved companion. We found that all the four previously investigated stars that were found to be ultra--depleted in Be are binaries. In two cases the companion is a white dwarf, and in the other two cases the companion might be a white dwarf or a main-sequence star. One new barium star was identified. We speculate that the interaction with the white dwarf progenitor caused an alteration in the abundance pattern of the star, which resulted in severe beryllium depletion. Possible mechanisms such as thermohaline mixing, episodic accretion, and rotational mixing are discussed. We also briefly discuss predictions for validating this scenario
We investigate the production of magnetic flux from rotating black holes in active galactic nuclei (AGNs) and compare it with the upper limit of ultrahigh energy cosmic ray (UHECR) luminosities, calculated from observed integral flux of GeV-TeV gamma rays for nine UHECR AGN sources. We find that, for the expected range of black hole rotations (0.44<a<0.80), the corresponding bounds of theoretical magnetic luminosities from AGNs coincides with the calculated UHECR luminosity. We argue that such result possibly can contribute to constrain AGN magnetic and dynamic properties as phenomenological tools to explain the requisite conditions to proper accelerate the highest energy cosmic rays.
Context: Studies based on high-precision abundance determinations revealed
that chemical patterns of solar twins are characterised by the correlation
between the differential abundances relative to the Sun and the condensation
temperatures (Tc) of the elements. It has been suggested that the origin of
this relation is related to the chemical evolution of the Galactic disk, but
other processes, associated with the presence of planets around stars, might
also be involved.
Aims: We analyse HIRES spectra of 14 solar twins and the Sun to provide new
insights on the mechanisms that can determine the relation between [X/H] and
Tc.
Methods: Our spectroscopic analysis produced stellar parameters (Teff, log g,
[Fe/H], and $\xi$), ages, masses, and abundances of 22 elements (C, O, Na, Mg,
Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, and Ba). We
used these determinations to place new constraints on the chemical evolution of
the Galactic disk and to verify whether this process alone can explain the
different [X/H]-Tc slopes observed so far.
Results: We confirm that the [X/Fe] ratios of all the species correlate with
age. The slopes of these relations allow us to describe the effect that the
chemical evolution of the Galactic disk has on the chemical patterns of the
solar twins. After subtracting the chemical evolution effect, we find that the
unevolved [X/H]-Tc slope values do not depend on the stellar ages anymore.
However, the wide diversity among these [X/H]-Tc slopes, covering a range of
$\pm$4~10$^{-5}$ dex K$^{-1}$, indicates that processes in addition to the
chemical evolution may affect the [X/H]-Tc slopes.
Conclusions: The wide range of unevolved [X/H]-Tc slope values spanned at all
ages by our sample could reflect the wide diversity among exo-planetary systems
observed so far and the variety of fates that the matter in circumstellar disks
can experience.
Galaxy morphologies and star-formation rates depend on environment. Galaxies in under-dense regions are generally star-forming and disky whereas galaxies in overdense regions tend to be early-type and not actively forming stars. The mechanism(s) responsible for star-formation quenching and morphological transformation remain unclear, although many processes have been proposed. We study the dependence of star-formation and morphology on X-ray luminosity for galaxies in Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) groups and clusters. While controlling for stellar and halo mass dependencies, we find that galaxies in X-ray strong groups and clusters have preferentially low star-forming and disk fractions -- with the differences being strongest at low stellar masses. The trends that we observe do not change when considering only galaxies found within or outside of the X-ray radius of the host group. When considering central and satellite galaxies separately we find that this dependence on X-ray luminosity is only present for satellites, and we show that our results are consistent with "galaxy stangulation" as a mechanism for quenching these satellites. We investigate the dynamics of the groups and clusters in the sample, and find that the velocity distributions of galaxies beyond the virial radius in low X-ray luminosity halos tend to be less Gaussian in nature than the rest of the data set. This may be indicative of low X-ray luminosity groups and clusters having enhanced populations of star-forming and disk galaxies as a result of recent accretion.
The presence of megaparsec-scale radio halos in galaxy clusters has already been established by many observations over the last two decades. The emerging explanation for the formation of these giant sources of diffuse synchrotron radio emission is that they trace turbulent regions in the intracluster medium, where particles are trapped and accelerated during cluster mergers. Our current observational knowledge is, however, mainly limited to massive systems. Here we present observations of a sample of 14 mass-selected galaxy clusters, i.e. $M_{\rm 500} > 4\times10^{14}$~M${_\odot}$, in the Southern Hemisphere, aimed to study the occurrence of radio halos in low mass clusters and test the correlation between the radio halo power at 1.4 GHz $P_{\rm 1.4}$ and the cluster mass $M_{\rm 500}$. Our observations were performed with the 7-element Karoo Array Telescope at 1.86 GHz. We found three candidates to host diffuse cluster-scale emission and derived upper limits at the level of $0.6 - 1.9 \times 10^{24}$~Watt~Hz$^{-1}$ for $\sim 50\%$ of the clusters in the sample, significantly increasing the number of clusters with radio halo information in the considered mass range. Our results confirm that bright radio halos in less massive galaxy clusters are statistically rare.
We present simulations of star forming filaments incorporating - to our knowledge - the largest chemical network used to date on-the-fly in a 3D-MHD simulation. The network contains 37 chemical species and about 300 selected reaction rates. For this we use the newly developed package KROME (Grassi et al. 2014). Our results demonstrate the feasibility of using such a complex chemical network in 3D-MHD simulations on modern supercomputers. We perform simulations with different strengths of the interstellar radiation field and the cosmic ray ionisation rate and find chemical and physical results in accordance with observations and other recent numerical work.
We investigate the dynamical evolution of 40 open clusters (OCs) by means of their astrophysical parameters derived from field-decontaminated 2MASS photometry. We find a bifurcation in the planes core radius vs. age and cluster radius vs. age, in which part of the clusters appear to expand with time probably due to the presence of stellar black holes while others seem to shrink due to dynamical relaxation. Mass functions (MFs) are built for 3$/$4 of the sample (31 OCs), which are used to search for indications of mass segregation and external dynamical processes by means of relations among astrophysical, structural and evolutionary parameters. We detect a flattening of MF slopes ocurring at the evolutionary parameters $\tau_{core}\leq 32$ and $\tau_{overall}\leq 30$, respectively. Within the uncertainties involved, the overall MF slopes of 14 out of 31 OCs with $m_{overall} > 500~M_{\odot}$ are consistent with Kroupa's initial mass function, implying little or no dynamical evolution for these clusters. The remaining 17 OCs with MF slopes departing from that of Kroupa show mild/large scale mass segregation due to dynamical evolution.
We present an extension to the time-dependent photo-ionization code C$^2$-Ray to calculate photo-heating in an efficient and accurate way. In C$^2$-Ray, the thermal calculation demands relatively small time-steps for accurate results. We describe two novel methods to reduce the computational cost associated with small time-steps, namely, an adaptive time-step algorithm and an asynchronous evolution approach. The adaptive time-step algorithm determines an optimal time-step for the next computational step. It uses a fast ray-tracing scheme to quickly locate the relevant cells for this determination and only use these cells for the calculation of the time-step. Asynchronous evolution allows different cells to evolve with different time-steps. The asynchronized clocks of the cells are synchronized at the times where outputs are produced. By only evolving cells which may require short time-steps with these short time-steps instead of imposing them to the whole grid, the computational cost of the calculation can be substantially reduced. We show that our methods work well for several cosmologically relevant test problems and validate our results by comparing to the results of another time-dependent photo-ionization code.
We have obtained high-spatial-resolution spectrophotometric data on several nearby spiral galaxies with the Southern African Large Telescope (SALT) Fabry-P\'erot interferometer on the Robert Stobie Spectrograph (RSS) as a part of the RSS Imaging spectroscopy Nearby Galaxy Survey (RINGS). We have successfully reduced two tracks of Fabry-P\'erot data for the galaxy NGC 2280 to produce a velocity field of the H-alpha line of excited hydrogen. We have modeled these data with the DiskFit modeling software and found these models to be in excellent agreement both with previous measurements in the literature and with our lower-resolution HI velocity field of the same galaxy. Despite this good agreement, small regions exist where the difference between the H-alpha and HI velocities is larger than would be expected from typical dispersions. We investigate these regions of high velocity difference and offer possible explanations for their existence.
Presented here is an independent re-analysis of the Kepler light curve of Kepler-91 (KIC 8219268). Using the EXONEST software package, which provides both Bayesian parameter estimation and Bayesian model testing, we were able to re-confirm the planetary nature of Kepler-91b. In addition to the primary and secondary eclipses of Kepler-91b, a third dimming event appears to occur approximately $60^o$ away (in phase) from the secondary eclipse, leading to the hypothesis that a Trojan planet may be located at the L4 or L5 Lagrange points. Here, we present a comprehensive investigation of four possibilities to explain the observed dimming event using all available photometric data from the Kepler Space Telescope, recently obtained radial velocity measurements, and N-body simulations. We find that the photometric model describing Kepler-91b and a Trojan planet is highly favored over the model involving Kepler-91b alone. However, it predicts an unphysically high temperature for the Trojan companion, leading to the conclusion that the extra dimming event is likely a false-postive.
There is now strong evidence that Long-duration Gamma-Ray Bursts (LGRBs) are preferentially formed in low-metallicity environments. However, the magnitude of this effect, and its functional dependence on metallicity have not been well characterized. In our previous paper, Graham & Fruchter (2013), we compared the metallicity distribution of LGRB host galaxies to the that of star forming galaxies in the local universe. Here we build upon this work by in effect dividing one distribution by the other, and thus directly determine the relative rate of LGRB formation as a function of metallicity in the low-redshift universe. We find a dramatic cutoff in LGRB formation above a metallicity of log(O/H)}+12 ~ 8.3 in the KK04 scale, with LGRBs forming >25 times more frequently per unit star-formation below this cutoff than above. Furthermore, our data suggests that the rate of LGRB formation per unit star formation continues to fall above this break. We estimate the LGRB formation rate per unit star formation may drop by as much as a factor of one hundred between one-third solar and solar metallicity.
Planets emit thermal radiation and reflect incident light that they recieve from their host stars. As a planet orbits it's host star the photometric variations associated with these two effects produce very similar phase curves. If observed through only a single bandpass this leads to a degeneracy between certain planetary parameters that hinder the precise characterization of such planets. However, observing the same planet through two different bandpasses gives one much more information about the planet. Here, we develop a Bayesian methodology for combining photometry from both \emph{Kepler} and the Transiting Exoplanet Survey Satellite (TESS). In addition, we demonstrate via simulations that one can disentangle the reflected and thermally emitted light from the atmosphere of a hot-Jupiter as well as more precisely constrain both the geometric albedo and dayside temperature of the planet. This methodology can further be employed using various combinations of photometry from the James Webb Space Telescope (JWST), the Characterizing ExOplanet Satellite (CHEOPS), or the PLATO mission.
Models are developed to simulate lightcurves of stars dimmed by transiting exoplanets with and without rings. These models are then applied to \textit{Kepler} photometry to search for planetary rings in a sample of 21 exoplanets, mostly hot Jupiters, chosen to offer the best observational opportunity for discovering potential rings. We also examine what kinds of rings might be expected for these planets, in terms of both size and orientation, based on arguments involving the host planet's equilibrium temperature, its likely obliquities, and the formation and stability of possible ring systems. Finding no evidence for rings, for each of the 21 studied planets it is determined on an observational basis which potential rings can be rejected out of a representative set of fiducial rings, varying in both size and orientation. For 12 of the 21 planets, we determined that Saturn-like rings could be ruled out for at least certain orientations. Additionally, the detectability of rings is studied, and it is found that ringed planets with small obliquities (roughly $5^{\circ}-10^{\circ}$) can yield large signals, which is encouraging for future work, since such small obliquities are expected for hot Jupiters.
More than 1500 exoplanets have been discovered around a large diversity of host stars (from M- to A-type stars). Tidal dissipation in their convective envelope is a key actor that shapes the orbital architecture of short-period systems and that still remains unknown. Using a simplified two-layer assumption and grids of stellar models, we compute analytically an equivalent modified tidal quality factor, which is proportional to the inverse of the frequency-averaged dissipation due to the viscous friction applied by turbulent convection on tidal waves. It leads the conversion of their kinetic energy into heat and tidal evolution of orbits and spin. During their Pre-Main-Sequence, all low-mass stars have a decrease of the equivalent modified tidal quality factor for a fixed angular velocity of their convective envelope. Next, it evolves on the Main Sequence to an asymptotic value that is minimum for $0.6M_{\odot}$ K-type stars and that increases by several orders of magnitude with increasing stellar mass. Finally, the rotational evolution of low-mass stars strengthens tidal dissipation during the Pre-Main-Sequence.
DarkSide-50 is the first physics detector of the DarkSide dark matter search program. The detector features a dual-phase underground-argon Time Projection Chamber (TPC) of 50 kg active mass surrounded by an organic liquid-scintillator neutron veto (30 tons) and a water-Cherenkov muon detector (1000 tons). The TPC is currently fully shielded and operating underground at Gran Sasso National Laboratory. A first run of 1422 kg-day exposure with atmospheric argon represents the most sensitive dark matter search using a liquid argon target. The TPC is now filled with underground argon, greatly reduced in 39Ar, and DarkSide-50 is in its final configuration for an extended dark matter search. Overviews of the design, performance, and results obtained so far with DarkSide-50 will be presented, along with future prospects for the DarkSide program.
The ``cosmic censorship conjecture'' asserts that all singularities arising from gravitational collapse are hidden within black holes. We investigate this conjecture in a setup of interest for tests of General Relativity: black hole solutions which are parametrically small deviations away from the Kerr solution. These solutions have an upper bound on rotation, beyond which a naked singularity is visible to outside observers. We study whether these (generic) spacetimes can be spun-up past extremality with point particles or accretion disks. Our results show that cosmic censorship is preserved for generic parameterizations. We also present examples of special geometries which can be spun-up past extremality.
We consider generic axially symmetric rotating spacetimes and examine particle collisions in the ergoregion. The results are generic and agree with those obtained in the particular case of the rotating Teo wormhole in N. Tsukamoto and C. Bambi, Phys. Rev. D 91, 104040 (2015). It is shown that for sufficiently rapid rotation, the energy of a particle escaping to infinity can become arbitrary large (so-called super-Penrose process). Moreover, this energy is typically much larger than the center-of mass energy of colliding particles. In this sense the situation differs radically from that for collisions near black holes.
The effects of charge exchange on waves propagating in weakly ionized plasmas are discussed. It is shown that for low-frequency processes, ions and neutrals should be treated as a single fluid with some effective charge on all of them. We have derived a new momentum equation which should be used in such an environment. As a result, the low-frequency magnetic waves can propagate even if particles are not magnetized, which is entirely due to the charge exchange and the fact that it is not possible to separate particles into two different populations as charged and neutral species. So there can be no friction force between ions and neutrals in the usual sense. The mean force per particle is proportional to the ionization ratio $n_i/(n_i+ n_n)$. Regarding the application of the theory to the Alfven wave propagation in the lower solar atmosphere, the results predict that the plane of displacement of the fluid must change by 90 degrees when an Alfven wave propagates from the area where particles are un-magnetized (photosphere) to the area where they are magnetized (chromosphere). Because of the most accurate cross sections which we have here, it is possible to very accurately determine altitudes at which such rotation of the Alfven wave takes place.
We consider the general scalar field Horndeski Lagrangian coupled to matter. Within this class of models, we present two results that are independent of the particular form of the model. First, we show that in a Friedmann-Robertson-Walker metric the Horndeski Lagrangian coincides with the pressure of the scalar field. Second, we employ the previous result to identify the most general form of the Lagrangian that allows for cosmological scaling solutions, i.e. solutions where the ratio of matter to field density and the equation of state remain constant. Scaling solutions of this kind may help solving the coincidence problem since in this case the presently observed ratio of matter to dark energy does not depend on initial conditions, but rather on the theoretical parameters.
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Context. Blazars are among the most energetic objects in the Universe. In
2008 August, Fermi/LAT detected the blazar PKS 1502+106 showing a rapid and
strong gamma-ray outburst followed by high and variable flux over the next
months. This activity at high energies triggered an intensive multi-wavelength
campaign covering also the radio, optical, UV, and X-ray bands indicating that
the flare was accompanied by a simultaneous outburst at optical/UV/X-rays and a
delayed outburst at radio bands.
Aims: In the current work we explore the phenomenology and physical
conditions within the ultra-relativistic jet of the gamma-ray blazar PKS
1502+106. Additionally, we address the question of the spatial localization of
the MeV/GeV-emitting region of the source.
Methods: We utilize ultra-high angular resolution mm-VLBI observations at 43
and 86 GHz complemented by VLBI observations at 15 GHz. We also employ
single-dish radio data from the F-GAMMA program at frequencies matching the
VLBI monitoring.
Results: PKS 1502+106 shows a compact core-jet morphology and fast
superluminal motion with apparent speeds in the range 5--22 c. Estimation of
Doppler factors along the jet yield values between ~7 up to ~50. This Doppler
factor gradient implies an accelerating jet. The viewing angle towards the
source differs between the inner and outer jet, with the former at ~3 degrees
and the latter at ~1 degree, after the jet bends towards the observer beyond 1
mas. The de-projected opening angle of the ultra-fast, magnetically-dominated
jet is found to be (3.8 +/- 0.5) degrees. A single jet component can be
associated with the pronounced flare both at high-energies and in radio bands.
Finally, the gamma-ray emission region is localized at less than 5.9 pc away
from the jet base.
Relativistically blurred reflection from the accretion disc provides a powerful probe of the extreme environments close to supermassive black holes; the inner regions of the accretion flow and the corona that produces the intense X-ray continuum. Techniques by which the geometry and extent of the corona can be measured through the observed X-ray spectrum are reviewed along with the evolution in the structure of the corona that is seen to accompany variations in the X-ray luminosity both on long and short timescales. Detailed analyses of the narrow line Seyfert 1 galaxies Markarian 335 and 1H0707-495, over observations with XMM-Newton as well as Suzaku and NuSTAR spanning nearly a decade reveal that increases in the X-ray luminosity coincide with an expansion of the corona to cover a larger area of the inner accretion disc. Underlying this long timescale variability lie more complex patterns of behaviour on short timescales. Flares in the X-ray emission during a low flux state of Mrk 335 observed in 2013 and 2014 are found to mark a reconfiguration of the corona while there is evidence that the flares were caused by a vertical collimation and ejection of coronal material, reminiscent of an aborted jet-launching event. Measurements of the corona and reflecting accretion disc are combined to infer the conditions on the inner disc that lead to the flaring event.
We investigate the Eddington ratio distribution of X-ray selected broad-line active galactic nuclei (AGN) in the redshift range 1.0<z<2.2, where the number density of AGNs peaks. Combining the optical and Subaru/FMOS near-infrared spectroscopy, we estimate black hole masses for broad-line AGNs in the Chandra Deep Field-South (CDF-S), Extended Chandra Deep Field-South (E-CDF-S), and the XMM-Newton Lockman Hole (XMM-LH) surveys. AGNs with similar black hole masses show a broad range of AGN bolometric luminosities, which are calculated from X-ray luminosities, indicating that the accretion rate of black holes is widely distributed. We find that a substantial fraction of massive black holes accreting significantly below the Eddington limit at z~2, in contrast to what is generally found for luminous AGNs at high redshift. Our analysis of observational selection biases indicates that the "AGN cosmic downsizing" phenomenon can be simply explained by the strong evolution of the co-moving number density at the bright end of the AGN luminosity function, together with the corresponding selection effects. However, it might need to consider a correlation between the AGN luminosity and the accretion rate of black holes that luminous AGNs have higher Eddington ratios than low-luminosity AGNs in order to understand the relatively small fraction of low-luminosity AGNs with high accretion rates in this epoch. Therefore, the observed downsizing trend could be interpreted as massive black holes with low accretion rates, which are relatively fainter than less massive black holes with efficient accretion.
We perform general-relativistic hydrodynamical simulations of dynamical capture binary neutron star mergers, emphasizing the role played by the neutron star spin. Dynamical capture mergers may take place in globular clusters, as well as other dense stellar systems, where most neutron stars have large spins. We find significant variability in the merger outcome as a function of initial neutron star spin. For cases where the spin is aligned with the orbital angular momentum, the additional centrifugal support in the remnant hypermassive neutron star can prevent the prompt collapse to a black hole, while for antialigned cases the decreased total angular momentum can facilitate the collapse to a black hole. We show that even moderate spins can significantly increase the amount of ejected material, including the amount unbound with velocities greater than half the speed of light, leading to brighter electromagnetic signatures associated with kilonovae and interaction of the ejecta with the interstellar medium. Furthermore, we find that the initial neutron star spin can strongly affect the already rich phenomenology in the post-merger gravitational wave signatures that arise from the oscillation modes of the hypermassive neutron star. In several of our simulations, the resulting hypermassive neutron star develops the one-arm ($m=1$) spiral instability, the most pronounced cases being those with small but non-negligible neutron star spins. For long-lived hypermassive neutron stars, the presence of this instability leads to improved prospects for detecting these events through gravitational waves, and thus may give information about the neutron star equation of state.
We study the distribution and evolution of highly ionised intergalactic metals in the Evolution and Assembly of Galaxies and their Environment (EAGLE) cosmological, hydrodynamical simulations. EAGLE has been shown to reproduce a wide range of galaxy properties while its subgrid feedback was calibrated without considering gas properties. We compare the predictions for the column density distribution functions (CDDFs) and cosmic densities of SiIV, CIV, NV, OVI and NeVIII absorbers with observations at redshift z = 0 to ~ 6 and find reasonable agreement, although there are some differences. We show that the typical physical densities of the absorbing gas increase with column density and redshift, but decrease with the ionization energy of the absorbing ion. The typical metallicity increases with both column density and time. The fraction of collisionally ionized metal absorbers increases with time and ionization energy. While our results show little sensitivity to the presence or absence of AGN feedback, increasing/decreasing the efficiency of stellar feedback by a factor of two substantially decreases/increases the CDDFs and the cosmic densities of the metal ions. We show that the impact of the efficiency of stellar feedback on the CDDFs and cosmic densities is largely due to its effect on the metal production rate. However, the temperatures of the metal absorbers, particularly those of strong OVI, are directly sensitive to the strength of the feedback.
We perform a systematic Bayesian analysis of rotation vs. dispersion support ($v_{\rm rot} / \sigma$) in $40$ dwarf galaxies throughout the Local Volume (LV) over a stellar mass range $10^{3.5} M_{\rm \odot} < M_{\star} < 10^8 M_{\rm \odot}$. We find that the stars in $\sim 90\%$ of the LV dwarf galaxies studied -- both satellites and isolated systems -- are dispersion-supported. In particular, we show that $7/10$ *isolated* dwarfs in our sample have stellar populations with $v_{\rm rot} / \sigma < 0.6$. All have $v_{\rm rot} / \sigma \lesssim 2$. These results challenge the traditional view that the stars in gas-rich dwarf irregulars (dIrrs) are distributed in cold, rotationally-supported stellar disks, while gas-poor dwarf spheroidals (dSphs) are kinematically distinct in having dispersion-supported stars. We see no clear trend between $v_{\rm rot} / \sigma$ and distance to the closest $\rm L_{\star}$ galaxy, nor between $v_{\rm rot} / \sigma$ and $M_{\star}$ within our mass range. We apply the same Bayesian analysis to four FIRE hydrodynamic zoom-in simulations of isolated dwarf galaxies ($10^9 M_{\odot} < M_{\rm vir} < 10^{10} M_{\rm \odot}$) and show that the simulated *isolated* dIrr galaxies have stellar ellipticities and stellar $v_{\rm rot} / \sigma$ ratios that are consistent with the observed population of dIrrs *and* dSphs without the need to subject these dwarfs to any external perturbations or tidal forces. We posit that most dwarf galaxies form as puffy, dispersion-supported systems, rather than cold, angular momentum-supported disks. If this is the case, then transforming a dIrr into a dSph may require little more than removing its gas.
We present accurate measurements of the linear, quadratic, and cubic local bias of dark matter halos, using curved "separate universe" N-body simulations which effectively incorporate an infinite-wavelength overdensity. This can be seen as an exact implementation of the peak-background split argument. We compare the results with the linear and quadratic bias measured from the halo-matter power spectrum and bispectrum, and find good agreement. On the other hand, the standard peak-background split applied to the Sheth & Tormen (1999) and Tinker et al. (2008) halo mass functions matches the measured linear bias parameter only at the level of 10%. The prediction from the excursion set-peaks approach performs much better, which can be attributed to the stochastic moving barrier employed in the excursion set-peaks prediction. We also provide convenient fitting formulas for the nonlinear bias parameters $b_2(b_1)$ and $b_3(b_1)$.
We measure the projected density profile, shape and alignment of the stellar and dark matter mass distribution in 11 strong-lens galaxies. We find that the projected dark matter density profile - under the assumption of a Chabrier stellar initial mass function - shows significant variation from galaxy to galaxy. Those with an outermost image beyond $\sim 10$ kpc are very well fit by a projected NFW profile; those with images within 10 kpc appear to be more concentrated than NFW, as expected if their dark haloes contract due to baryonic cooling. We find that over several half-light radii, the dark matter haloes of these lenses are rounder than their stellar mass distributions. While the haloes are never more elliptical than $e_{dm} = 0.2$, their stars can extend to $e_* > 0.2$. Galaxies with high dark matter ellipticity and weak external shear show strong alignment between light and dark; those with strong shear ($\gamma \gtrsim 0.1$) can be highly misaligned. This is reassuring since isolated misaligned galaxies are expected to be unstable. Our results provide a new constraint on galaxy formation models. For a given cosmology, these must explain the origin of both very round dark matter haloes and misaligned strong-lens systems.
The Local Group of galaxies offer some of the most discriminating tests of models of cosmic structure formation. For example, observations of the Milky Way (MW) and Andromeda satellite populations appear to be in disagreement with N-body simulations of the "Lambda Cold Dark Matter" ({\Lambda}CDM) model: there are far fewer satellite galaxies than substructures in cold dark matter halos (the "missing satellites" problem); dwarf galaxies seem to avoid the most massive substructures (the "too-big-to-fail" problem); and the brightest satellites appear to orbit their host galaxies on a thin plane (the "planes of satellites" problem). Here we present results from APOSTLE (A Project Of Simulating The Local Environment), a suite of cosmological hydrodynamic simulations of twelve volumes selected to match the kinematics of the Local Group (LG) members. Applying the Eagle code to the LG environment, we find that our simulations match the observed abundance of LG galaxies, including the satellite galaxies of the MW and Andromeda. Due to changes to the structure of halos and the evolution in the LG environment, the simulations reproduce the observed relation between stellar mass and velocity dispersion of individual dwarf spheroidal galaxies without necessitating the formation of cores in their dark matter profiles. Satellite systems form with a range of spatial anisotropies, including one similar to that of the MW, confirming that such a configuration is not unexpected in {\Lambda}CDM. Finally, based on the observed velocity dispersion, size, and stellar mass, we provide new estimates of the maximum circular velocity for the halos of nine MW dwarf spheroidals.
The loss of mass from protostars, in the form of a jet or outflow, is a necessary counterpart to protostellar mass accretion. Outflow ejection events probably vary in their velocity and/or in the rate of mass loss. Such `episodic' ejection events have been observed during the Class 0 protostellar phase (the early accretion stage), and continue during the subsequent class I phase that marks the first one million years of star formation. Previously observed episodic-ejection sources were relatively isolated; however, the most common sites of star formation are clusters. Outflows link protostars with their environment and provide a viable source of turbulence that is necessary for regulating star formation in clusters, but it is not known how an accretion-driven jet or outflow in a clustered environment manifests itself in its earliest stage. This early stage is important in establishing the initial conditions for momentum and energy transfer to the environment as the protostar and cluster evolve. Here we report that an outflow from a very young class 0 protostar, at the hub of the very active and filamentary Serpens South protostellar cluster, shows unambiguous episodic events. The $^{12}$CO (J=2-1) emission from the protostar reveals 22 distinct features of outflow ejecta, the most recent having the highest velocity. The outflow forms bipolar lobes --- one of the first detectable signs of star formation --- which originate from the peak of 1-mm continuum emission. Emission from the surrounding C$^{18}$O envelope shows kinematics consistent with rotation and an infall of material onto the protostar. The data suggest that episodic accretion-driven outflow begins in the earliest phase of protostellar evolution, and that the outflow remains intact in a very clustered environment, probably providing efficient momentum transfer for driving turbulence.
We introduce a method for identifying "twin" Type Ia supernovae, and using them to improve distance measurements. This novel approach to Type Ia supernova standardization is made possible by spectrophotometric time series observations from the Nearby Supernova Factory (SNfactory). We begin with a well-measured set of supernovae, find pairs whose spectra match well across the entire optical window, and then test whether this leads to a smaller dispersion in their absolute brightnesses. This analysis is completed in a blinded fashion, ensuring that decisions made in implementing the method do not inadvertently bias the result. We find that pairs of supernovae with more closely matched spectra indeed have reduced brightness dispersion. We are able to standardize this initial set of SNfactory supernovae to 0.083 +/- 0.012 magnitudes, implying a dispersion of 0.072 +/- 0.010 magnitudes in the absence of peculiar velocities. We estimate that with larger numbers of comparison SNe, e.g, using the final SNfactory spectrophotometric dataset as a reference, this method will be capable of standardizing high-redshift supernovae to within 0.06 +/-0.07 magnitudes. These results imply that at least 3/4 of the variance in Hubble residuals in current supernova cosmology analyses is due to previously unaccounted-for astrophysical differences among the supernovae
Quasars are the most luminous non-transient sources in the epoch of cosmological reionization (i.e., which ended a billion years after the Big Bang, corresponding to a redshift of z ~ 5), and are powerful probes of the inter-galactic medium at that time. This review covers current efforts to identify high-redshift quasars and how they have been used to constrain the reionization history. This includes a full description of the various processes by which neutral hydrogen atoms can absorb/scatter ultraviolet photons, and which lead to the Gunn-Peterson effect, dark gap and dark pixel analyses, quasar near zones and damping wing absorption. Finally, the future prospects for using quasars as probes of reionization are described.
The elegance of inflationary cosmology and cosmological perturbation theory ends with the formation of the first stars and galaxies, the initial sources of light that launched the phenomenologically rich process of cosmic reionization. Here we review the current understanding of early star formation, emphasizing unsolved problems and technical challenges. We begin with the first generation of stars to form after the Big Bang and trace how they influenced subsequent star formation. The onset of chemical enrichment coincided with a sharp increase in the overall physical complexity of star forming systems. Ab-initio computational treatments are just now entering the domain of the predictive and are establishing contact with local observations of the relics of this ancient epoch.
Studies of the physical properties of Trans-Neptunian Objects (TNOs) are a powerful probe into the processes of planetesimal formation and solar system evolution. JWST will provide unique new capabilities for such studies. Here we outline where the capabilities of JWST open new avenues of investigation, potential valuable observations and surveys, and conclude with a discussion of community actions that may serve to enhance the eventual science return of JWSTs TNO observations.
We review the observable consequences of the epoch of reionization (EoR) on the cosmic microwave background (CMB), and the resulting constraints on the EoR. We discuss how Thomson scattering with the free electrons produced during EoR equates to an optical depth for CMB photons. The optical depth measurements from the WMAP and Planck satellites, using large-scale CMB polarization power spectra, is one of the few current constraints on the timing of cosmic reionization. We also present forecasts for the precision with which the optical depth will be measured by future satellite missions. Second, we consider the kinematic Sunyaev-Zel'dovich (kSZ) effect, and how the kSZ power spectrum depends on the duration of reionization. We review current measurements of the kSZ power and forecasts for future experiments. Finally, we mention proposals to look for spectral distortions in the CMB that are related to the electron temperature at EoR, and ideas to map the variations in the optical depth across the sky.
The initial mass function (IMF) is an essential tool with which to study star formation processes. We have initiated the photometric survey of young open clusters in the Galaxy, from which the stellar IMFs are obtained in a homogeneous way. A total of 16 famous young open clusters have preferentially been studied up to now. These clusters have a wide range of surface densities (log sigma = -1 to 3 [stars pc^2] for stars with mass larger than 5M_sun) and cluster masses (M_cl = 165 to 50,000M_sun), and also are distributed in five different spiral arms in the Galaxy. It is possible to test the dependence of star formation processes on the global properties of individual clusters or environmental conditions. We present a preliminary result on the variation of the IMF in this paper.
The presence of elements heavier than helium ("metals") is of fundamental importance for a large number of astrophysical processes occurring in planet, star and galaxy formation; it also affects cosmic structure formation and evolution in several ways. Even a small amount of heavy elements can dramatically alter the chemistry of the gas, opening the path to complex molecules. Metals might enhance the ability of the gas to radiate away its thermal energy, thus favoring the formation of gravitationally bound objects; they can also condensate in a solid phase (dust grains), partly or totally blocking radiation from luminous sources. Finally, they represent useful tracers of energy deposition by stars and probe the physical properties of the environment by absorption or emission lines. Last, but certainly not least, life -- as we know it on Earth -- is tightly related to the presence of at least some of the heavy elements. In this pedagogical review I will concentrate on the connection between early metal enrichment and cosmic reionization. As we will see these two processes are intimately connected and their joint study might turn out to be fundamental in understanding the overall evolution of the Universe during the first billion years after the Big Bang, an epoch corresponding to redshifts z>6.
In this introductory chapter, we outline expectations for when and how the hydrogen and helium atoms in the universe turned from neutral to ionized, focusing on the earliest, least well understood stages, and emphasizing the most important open questions. We include a historical summary, and highlight the role of reionization as one of the few milestones in the evolution of the universe since the Big Bang, and its status as a unique probe of the beginning stages of structure formation.
One of the most exciting probes of the early phases of structure formation and reionization is the spin-flip line of neutral hydrogen, with a rest wavelength of 21 cm. This chapter introduces the physics of this transition and the astrophysical parameters upon which it depends, including discussions of the radiation fields that permeate the intergalactic medium that fix the brightness of this transition. We describe the critical points in the evolution of the 21-cm background and focus on the sky-averaged brightness and the power spectrum as representative measurements. Finally, we include a discussion of observations and the challenges they face in the near future.
Star-forming galaxies in the early universe provide us with perhaps the most natural way of explaining the reionization of the universe. Current observational results are sufficiently comprehensive, as to allow us to approximately calculate how the ionizing radiation from galaxies varies as a function of cosmic time. Important uncertainties in modeling reionization by galaxies revolve around the escape fraction and its luminosity and redshift dependence, a possible truncation of the galaxy luminosity function at the faint end, and an evolution in the production efficiency of Lyman-continuum photons with cosmic time. Despite these uncertainties, plausible choices for these parameters naturally predict a cosmic ionizing emissivity at z~6-10 whose evolution and overall normalization is in excellent agreement with that derived from current observational constraints. This strongly suggests that galaxies provide the necessary photons to reionize the universe.
We present continuum and molecular line observations at 230 GHz and 345 GHz from the Sub-millimeter Array (SMA) toward three protostars in the Perseus L1448N region. The data are from the large project "Mass Assembly of Stellar Systems and their Evolution with the SMA" (MASSES). Three dust continuum sources, Source B, Source NW, and Source A, are detected at both frequencies. These sources have corresponding emission peaks in C18O (J=2-1), 13CO (J=2-1), and HCO+ (J=4-3), and have offsets with N2D+ (J=3-2) peaks. High angular resolution data from a complimentary continuum survey with the Karl G. Jansky Very Large Array show that Source B is associated with three 8 mm continuum objects, Source NW with two, and Source A remains single. These results suggest that multiplicity in L1448N exists at different spatial scales from a few thousand AU to < 100 AU. Velocity gradients in each source obtained from two-dimensional fits to the SMA C18O emission are found to be perpendicular to within 20 degrees of the outflow directions as revealed by 12CO (J=2-1). We have observed that Sources B and NW with multiplicity have higher densities than Source A without multiplicity. This suggests that thermal Jeans fragmentation can be relevant in the fragmentation process. However, we have not observed a difference in the ratio between rotational and gravitational energy between sources with and without multiplicity. We also have not observed a trend between non-thermal velocity dispersions and the level of fragmentation. Our study has provided the first direct and comprehensive comparison between multiplicity and core properties in low-mass protostars, although based on small number statistics.
To ensure progress in astronomy over the coming decades, the key questions are "what facilities will we build, and when?" Toward this end, the Association of Universities for Research in Astronomy (AURA) recently commissioned a study on future space-based options for UV and optical astronomy. The resulting study - "From Cosmic Births to Living Earths" - concluded that a space telescope equipped with a 12-meter class primary mirror would make fundamental advances across virtually all of astrophysics, including finding and characterizing the atmospheres of dozens of Earth-like planets. This ambitious telescope concept is referred to as the High Definition Space Telescope (HDST). In a recent arXiv white paper, Elvis (2015) critiqued a subset of the findings of the AURA study, focusing on the detection and characterization of rocky exoplanets in the habitable zone. In this response, we clarify these issues to confirm that HDST would play a transformative role in the study of terrestrial worlds. Its capabilities for studying exoplanets would be truly unique, even in 2035, and would complement HDST's broad and deep range of exciting astrophysics.
We exploit the first public data release of VIPERS to investigate environmental effects in galaxy evolution between $z\sim0.5$ and $0.9$. The large number of spectroscopic redshifts over an area of about $10\,\mathrm{deg}^2$ provides a galaxy sample with high statistical power. The accurate redshift measurements, with $\sigma_z = 0.00047(1+z_\mathrm{spec})$, allow us to robustly isolate galaxies living in the lowest- and highest-density environments, as defined in terms of spatial 3D density contrast. We estimate the stellar mass function (SMF) of galaxies residing in these two environments, and constrain its high-mass end with unprecedented precision. We find that the galaxy SMF in the densest regions has a different shape than that measured at low densities, with an enhancement of massive galaxies and a hint of a flatter (less negative) slope at $z<0.8$. We normalise each SMF to the comoving volume occupied by the corresponding environment, and relate estimates from different redshift bins. We observe an evolution of the SMF of VIPERS galaxies in high densities, while the low-density one is nearly constant. We compare these results to semi-analytical models and find consistent environmental signatures. We discuss how the halo mass function and fraction of central/satellite galaxies depend on the environments considered, making intrinsic and environmental properties of galaxies physically coupled, and therefore difficult to disentangle. The evolution of our low-density regions is well described by the formalism introduced by Peng et al.~(2010), and is consistent with the idea that galaxies become progressively passive because of internal physical processes. The same formalism could also describe the evolution of the SMF in the high density regions, but only if a significant contribution from dry mergers is considered. [Abridged]
Colliding Wolf-Rayet (WR) winds produce thermal X-ray emission widely observed by X-ray telescopes. In wide WR+O binaries, such as WR 140, the X-ray flux is tied to the orbital phase, and is a direct probe of the winds' properties. In the Galactic center, $\sim$30 WRs orbit the super massive black hole (SMBH) within $\sim$10", leading to a smorgasbord of wind-wind collisions. To model the X-ray emission of WR 140 and the Galactic center, we perform 3D hydrodynamic simulations to trace the complex gaseous flows, and then carry out 3D radiative transfer calculations to compute the variable X-ray spectra. The model WR 140 RXTE light curve matches the data well for all phases except the X-ray minimum associated with periastron, while the model spectra agree with the RXTE hardness ratio and the shape of the Suzaku observations throughout the orbit. The Galactic center model of the Chandra flux and spectral shape match well in the region r$<$3", but the model flux falls off too rapidly beyond this radius.
With the design and development of next-generation high-energy neutrino detectors, it is important to compare different detector designs to optimize detection probability and science reach. These comparisons are nevertheless difficult due to large uncertainties in current neutrino source model parameters. We examine the role of the most important characteristics of high-energy neutrino searches in the probability of discovering different sources types. We derive scaling relations for each considered source and search scenario, which can be used to compare different detector designs with respect to their utility in discovering different source populations. The recovered scaling relations are independent of source strengths, providing a model-independent comparison.
The OI 777 nm lines are among the most commonly used diagnostics for the oxygen abundances in the atmospheres of FGK-type stars. However, they form in conditions that are far from local thermodynamic equilibrium (LTE). We explore the departures from LTE of atomic oxygen, and their impact on OI lines, across the Stagger-grid of three-dimensional hydrodynamic model atmospheres. For the OI 777 nm triplet we find significant departures from LTE. These departures are larger in stars with larger effective temperatures, smaller surface gravities, and larger oxygen abundances. We present grids of predicted 3D non-LTE based equivalent widths for the OI616nm, [OI] 630 nm, [OI] 636 nm, and OI 777 nm lines, as well as abundance corrections to 1D LTE based results.
The rapid analysis of ongoing gravitational microlensing events has been integral to the successful detection and characterisation of cool planets orbiting low mass stars in the Galaxy. In this paper we present an implementation of search and fit techniques on Graphical Processing Unit hardware. The method allows for the rapid identification of candidate planetary microlensing events and their subsequent followup for detailed characterisation.
The Galactic Center (GC) has been long known to host gamma-ray emission detected to >10 TeV. HESS data now points to two plausible origins: the supermassive black hole (perhaps with >PeV cosmic rays and neutrinos) or high-energy electrons from the putative X-ray pulsar wind nebula G359.95-0.04. We show that if the magnetic field experienced by PWN electrons is near the several mG ambient field strength suggested by radio observations of the nearby GC magnetar SGR J1745-29, synchrotron losses constrain the TeV gamma-ray output to be far below the data. Accounting for the peculiar geometry of GC infrared emission, we also find that the requisite TeV flux could be reached if the PWN is ~1 pc from Sgr A* and the magnetic field is two orders of magnitude weaker, a scenario that we discuss in relation to recent data and theoretical developments. Otherwise, Sgr A* is left, which would then be a PeV link to other AGN.
Winds outflowing from Active Galactic Nuclei (AGNs) may carry significant amount of mass and energy out to their host galaxies. In this paper we report the detection of a sub-relativistic outflow observed in the Narrow Line Seyfert 1 Galaxy IRAS17020+4544 as a series of absorption lines corresponding to at least 5 absorption components with an unprecedented wide range of associated column densities and ionization levels and velocities in the range of 23,000-33,000 km/s, detected at X-ray high spectral resolution (E/Delta E ~1000) with the ESA's observatory XMM-Newton. The charge states of the material constituting the wind clearly indicate a range of low to moderate ionization states in the outflowing gas and column densities significantly lower than observed in highly ionized ultra fast outflows. We estimate that at least one of the outflow components may carry sufficient energy to substantially suppress star formation, and heat the gas in the host galaxy. IRAS17020+4544 provides therefore an interesting example of feedback by a moderately luminous AGN hosted in a spiral galaxy, a case barely envisaged in most evolution models, which often predict that feedback processes take place in massive elliptical galaxies hosting luminous quasars in a post merger phase.
Recent observations of protoplanetary disk have reported spiral structures that are potential signatures of embedded planets, and modeling efforts have shown that a single planet can excite multiple spiral arms, in contrast to conventional disk-planet interaction theory. Using two and three-dimensional hydrodynamics simulations to perform a systematic parameter survey, we confirm the existence of multiple spiral arms in disks with a single planet, and discover a scaling relation between the azimuthal separation of the primary and secondary arm, $\phi_{\rm sep}$, and the planet-to-star mass ratio $q$: $\phi_{\rm sep} = 102^{\circ} (q/0.001)^{0.2}$ for companions between Neptune mass and 16 Jupiter masses around a 1 solar mass star, and $\phi_{\rm sep} = 180^{\circ}$ for brown dwarf mass companions. This relation is independent of the disk's temperature, and can be used to infer a planet's mass to within an accuracy of about 30% given only the morphology of a face-on disk. Combining hydrodynamics and Monte-Carlo radiative transfer calculations, we verify that our numerical measurements of $\phi_{\rm sep}$ are accurate representations of what would be measured in near-infrared scattered light images, such as those expected to be taken by Gemini/GPI, VLT/SPHERE, or Subaru/SCExAO in the future. Finally, we are able to infer, using our scaling relation, that the planet responsible for the spiral structure in SAO 206462 has a mass of about 6 Jupiter masses.
Silicon direct bonding offers flexibility in the design and development of Si optics by allowing manufacturers to combine subcomponents with a potentially lossless and mechanically stable interface. The bonding process presents challenges in meeting the requirements for optical performance because air gaps at the Si interface cause large Fresnel reflections. Even small (35 nm) gaps reduce transmission through a direct bonded Si compound optic by 4% at $\lambda = 1.25 \; \mu$m at normal incidence. We describe a bond inspection method that makes use of precision slit spectroscopy to detect and measure gaps as small as 14 nm. Our method compares low finesse Fabry-P\'{e}rot models to high precision measurements of transmission as a function of wavelength. We demonstrate the validity of the approach by measuring bond gaps of known depths produced by microlithography.
A major goal of observational and theoretical cosmology is to observe the largely unexplored time period in the history of our universe when the first galaxies form, and to interpret these measurements. Early galaxies dramatically impacted the gas around them in the surrounding intergalactic medium (IGM) by photoionzing the gas during the Epoch of Reionization (EoR). This epoch likely spanned an extended stretch in cosmic time: ionized regions formed and grew around early generations of galaxies, gradually filling a larger and larger fraction of the volume of the universe. At some time -- thus far uncertain, but within the first billion years or so after the big bang -- essentially the entire volume of the universe became filled with ionized gas. The properties of the IGM provide valuable information regarding the formation time and nature of early galaxy populations, and many approaches for studying the first luminous sources are hence based on measurements of the surrounding intergalactic gas. The prospects for improved reionization-era observations of the IGM and early galaxy populations over the next decade are outstanding. Motivated by this, we review the current state of models of the IGM during reionization. We focus on a few key aspects of reionization-era phenomenology and describe: the redshift evolution of the volume-averaged ionization fraction, the properties of the sources and sinks of ionizing photons, along with models describing the spatial variations in the ionization fraction, the ultraviolet radiation field, the temperature of the IGM, and the gas density distribution.
Asteroids belonging to the Ch spectral taxonomic class are defined by the presence of an absorption near 0.7 {\mu}m, which is interpreted as due to Fe-bearing phyllosilicates. Phyllosilicates also cause strong absorptions in the 3-{\mu}m region, as do other hydrated and hydroxylated minerals and H2O ice. Over the past decade, spectral observations have revealed different 3-{\mu}m band shapes the asteroid population. Although a formal taxonomy is yet to be fully established, the "Pallas-type" spectral group is most consistent with the presence of phyllosilicates. If Ch class and Pallas type are both indicative of phyllosilicates, then all Ch-class asteroids should also be Pallas-type. In order to test this hypothesis, we obtained 42 observations of 36 Ch-class asteroids in the 2- to 4-{\mu}m spectral region. We found that 88% of the spectra have 3-{\mu}m band shapes most consistent with the Pallas-type group. This is the first asteroid class for which such a strong correlation has been found. Because the Ch class is defined by the presence of an absorption near 0.7 {\mu}m, this demonstrates that the 0.7-{\mu}m band serves not only as a proxy for the presence of a band in the 3-{\mu}m region, but specifically for the presence of Pallas-type bands. There is some evidence for a correlation between band depth at 2.95 {\mu}m and absolute magnitude and/or albedo. However, we find only weak correlations between 2.95-{\mu}m band depth and semi-major axis. The connection between band depths in the 0.7- and 3-{\mu}m regions is complex and in need of further investigation.
In this paper, we propose observational methods for detecting lightning in protoplanetary disks. We do so by calculating the critical electric field strength in the lightning matrix gas (LMG), the parts of the disk where the electric field is strong enough to cause lightning. That electric field accelerates multiple positive ion species to characteristic terminal velocities. In this paper, we present three distinct discharge models, with corresponding critical electric fields. We simulate the position-velocity diagrams and the integrated emission maps for the models. We calculate the measure of sensitivity values for detection of the models, and for distinguishing between the models. At the distance of TW-Hya (54pc), LMG that occupies $2\pi$ in azimuth and $25 \mathrm{au}<r<50 \mathrm{au}$ is $1200\sigma$- to $4000\sigma$-detectable. The lower limits of the radii of $5\sigma$-detectable LMG clumps are between 1.6 au and 5.3 au, depending on the models.
We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc$^{-2}$ to over 10,000 pc$^{-2}$, with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifying clusters and groups as continuous regions with surface densities $\ge10$ pc$^{-2}$, we find that 59% of the YSOs are in the largest cluster, the Orion Nebular Cluster (ONC), while 13% of the YSOs are found in a distributed population. A lower fraction of protostars in the distributed population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups show that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only $\sim 2$ Myr in age. We find the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or by dynamical interactions in dense, clustered regions.
Supermassive black holes (SMBHs) can capture and tidally disrupt stars or sub-stellar objects orbiting nearby. The detections of Sw J1644+57-like events suggest that at least some TDEs can launch a relativistic jet beaming towards Earth. A natural expectation would be the existence of TDEs with a relativistic jet beaming away from Earth. The nearby TDE candidate IGR J12580+0134 provides new insights into the jet phenomenon. Combining several constraints, we find that the event invokes a $8-40$ Jupiter mass object tidally disrupted by a $3 \times 10^5 - 1.8 \times 10^7 M_\sun$ SMBH. Recently, a bright radio transient was discovered by Irwin et al. in association with IGR J12580+0134. We perform detailed modeling of the event based on a numerical jet model previously developed for the radio emission of Sw J1644+57. We find that the radio data of IGR J12580+0134 can be interpreted within an external forward shock model in the Newtonian regime. Using Sw J1644+57 as a template and properly correcting for its luminosity, we argue that the observed X-ray flux in early times is too faint to allow an on-beam relativistic jet unless the Lorentz factor is very small. Rather, the X-ray emission is likely from the disk or corona near the black hole. From various constraints, we find that the data are consistent with an off-beam relativistic jet with a viewing angle $\theta_{\rm obs} \gtrsim 30^{\rm o}$, and an initial Lorentz factor $\Gamma_j \gtrsim $ a few.This scenario can readily be tested in the upcoming VLBI observations.
Neutral diffuse intergalactic gas that existed during the Epoch of Reionization (EoR) suppresses Lyman Alpha (Lya) flux emitted by background galaxies. In this chapter I summarise the increasing observational support for the claim that Lya photons emitted by galaxies at z>6 are suppressed by intervening HI gas. I describe key physical processes that affect Lya transfer during the EoR. I argue that in spite of the uncertainties associated with this complex multiscale problem, the data on Lya emitting galaxies at z=0-6 strongly suggests that the observed reduction in Lya flux from galaxies at z>6 is due to additional intervening HI gas. The main question is what fraction of this additional HI gas is in the diffuse neutral IGM. I summarise how future surveys on existing and upcoming instruments are expected to reduce existing observational uncertainties enormously. With these improved data we will likely be able to nail down reionization with Lya emitting galaxies.
The anisotropies of the B-mode polarization in the cosmic microwave background radiation play a crucial role for the study of the very early Universe. However, in the real observation, the mixture of the E-mode and B-mode can be caused by the partial sky surveys, which must be separated before applied to the cosmological explanation. The separation method developed by Smith (\citealt{PhysRevD.74.083002}) has been widely adopted, where the edge of the top-hat mask should be smoothed to avoid the numerical errors. In this paper, we compare three different smoothing methods, and investigate the leakage residuals of the E-B mixture. We find that, if the less information loss is needed and the smaller region is smoothed in the analysis, the \textit{sin}- and \textit{cos}-smoothing methods are better. However, if we need a clean constructed B-mode map, the larger region around the mask edge should be smoothed. In this case, the \textit{Gaussian}-smoothing method becomes much better. In addition, we find that the leakage caused by the numerical errors in the \textit{Gaussian}-smoothing method mostly concentrates on two bands, which is quite easy to be reduced for the further E-B separations.
The gamma-ray binary system PSR B1259-63/LS 2883 went through periastron in May 2014. We report on the optical spectroscopic monitoring of the system from 33 d before to 78 d after periastron, undertaken with the Southern African Large Telescope (SALT). The H{\alpha} and He I ({\lambda}6678) lines exhibit an orbital variation around periastron, with the line strengths reaching a maximum ~13 d after periastron. The line strength is weaker than observed around the previous periastron in 2010. There is also a marked change in the line-strength and asymmetry around the first disc crossing. These observations are consistent with the disruption of the circumstellar disc around periastron due to the interaction with the pulsar.
A supra-massive neutron star (NS) spinning extremely rapidly could survive from a merger of NS-NS binary. The spin-down of this remnant NS that is highly magnetized would power the isotropic merger ejecta to produce a bright mergernova emission in ultraviolet/optical bands. Before the mergernova, the early interaction between the NS wind and the ejecta can drive a forward shock to propagate outwards into the ejecta. As a result, a remarkable amount of heat can be accumulated to be deposited behind the shock front, the final escaping of which can produce a shock breakout emission. We describe the dynamics and thermal emission of this shock with a semi-analytical model. It is found that a sharp and luminous breakout emission, which is mainly in soft X-rays with a luminosity of $\sim10^{45}~\rm erg~s^{-1}$, appears at a few hours after the merger, by leading the mergernova emission as a precursor. Therefore, detections of such X-ray precursors would provide a smoking-gun evidence for identifying NS-powered mergernovae and distinguishing them from the radioactive-powered ones (i.e., kilonovae or macronovae). The discovery of NS-powered mergernovae would finally help to confirm the gravitational wave signals due to the mergers and the existence of supra-massive NSs.
We carried out observations toward the giant molecular cloud W 37 with the $J = 1 - 0$ transitions of $^{12}$CO, $^{13}$CO, and C$^{18}$O using the 13.7 m single-dish telescope at the Delingha station of Purple Mountain Observatory. Based on the three CO lines, we calculated the column densities, cloud masses for the molecular clouds with radial velocities at around $+20 \mathrm{km s}^{-1}$. The gas mass of W 37, calculated from $^{13}$CO emission, is $1.7\times10^5 M_\odot$, above the criteria of giant molecular cloud. The dense ridge of W 37 is a dense filament, which is supercritical in linear mass ratio. Dense clumps found by C$^{18}$O emission are aligned along the dense ridge with a regular interval about 2.8 pc, similar to the clump separation caused by large-scale `sausage instability'. We confirm the identification of the giant molecular filament (GMF) G 18.0-16.8 by \cite{2014A&A...568A..73R} and find a new giant filament, G16.5-15.8, located in the west 0.8 degree of G 18.0-16.8. Both GMFs are not gravitationally bound, as indicated by their low linear mass ratio ($\sim80 M_\odot \mathrm{pc}^{-1}$). We compared the gas temperature map with the dust temperature map from \emph{Herschel} images, and find similar structures. The spatial distributions of class I objects and the dense clumps is reminiscent of triggered star formation occurring in the northwestern part of W 37, which is close to NGC 6611.
Recently, the presence of fullerenes in the interstellar medium (ISM) has been confirmed, especially with the first confirmed identification of two strong diffuse interstellar bands (DIBs) with C60+. This justifies reassesing the importance of interstellar fullerenes of various sizes with endohedral or exohedral inclusions and heterofullerenes (EEHFs). The phenomenology of fullerenes is complex. In addition to formation in shock shattering, fully dehydrogenated PAHs in diffuse interstellar (IS) clouds could perhaps efficiently transform into fullerenes including EEHFs. But it is extremely difficult to assess their expected abundance, composition and size distribution, except for C60+. As often suggested, EEHFs share many properties with C60, as regards stability, formation/destruction, chemical processes and many basic spectral features. We address the importance of various EEHFs as possible DIB carriers. Specifically, we discuss IS properties and the contributions of fullerenes of various sizes and charge such as C60+, metallofullerenes, heterofullerenes, fulleranes, fullerene-PAH compounds, H2@C60. We conclude that the landscape of IS fullerenes is probably much richer than heretofore realized. As has been suggested previously, EEHFs, together with pure fullerenes of various sizes, have properties necessary to be suitably carriers of DIBs (carbonaceous nature, resilience in the ISM, various heteroatoms and ionization states, relatively easy formation, few isomers, right wavelength range, energy internal conversion, Jahn-Teller fine structure) as supported by the C60+ DIBs. But, the lack of information about optical spectra other than C60 and IS abundances still precludes defined assessment of the importance of fullerenes as DIB carriers. Their compounds could significantly contribute to DIBs, but it still seems difficult that they are the only important DIB carriers.
The cascade of kinetic Alfv\'en waves (KAWs) at the sub-ion scales in the solar wind is numerically simulated using a fluid approach that retains ion and electron Landau damping, together with ion finite Larmor radius corrections. Assuming initially equal and isotropic ion and electron temperatures, and an ion beta equal to unity, different simulations are performed by varying the propagation direction and the amplitude of KAWs that are randomly driven at a transverse scale of about one fifth of the proton gyroradius in order to maintain a prescribed level of turbulent fluctuations. The resulting turbulent regimes are characterized by the nonlinearity parameter, defined as the ratio of the characteristic times of Alfv\'en wave propagation and of the transverse nonlinear dynamics. The corresponding transverse magnetic energy spectra display power laws with exponents spanning a range of values consistent with spacecraft observations. The meandering of the magnetic field lines together with the ion temperature homogenization along these lines are shown to be related to the strength of the turbulence, measured by the nonlinearity parameter. The results are interpreted in terms of a recently proposed phenomenological model where the homogenization process along field lines induced by Landau damping plays a central role.
As a part of the long-term program at Kitt Peak National Observatory (KPNO), the Mn I 539.4 nm line has been observed for nearly three solar cycles using the McMath telescope and the 13.5 m spectrograph in double-pass mode. These full-disk spectrophotometric observations revealed an unusually strong change of this line's parameters over the solar cycle. Optical pumping by the Mg II k line was originally proposed to explain these variations. More recent studies have proposed that this is not required and that the magnetic variability might explain it. Magnetic variability is also the mechanism that drives the changes in total solar irradiance variations (TSI). With this work we investigate this proposition quantitatively by using using the model SATIRE-S. We applied exactly the same model atmospheres and value of the free parameter as were used in previous solar irradiance reconstructions to now model the variation in the Mn I 539.4 nm line profile and in neighboring Fe I lines. We compared the results of the theoretical model with KPNO observations. Our result confirms that optical pumping of the Mn I 539.4 nm line by Mg II k is not the main cause of its solar cycle change. It also provides independent confirmation of solar irradiance models which are based on the assumption that irradiance variations are caused by the evolution of the solar surface magnetic flux. The result obtained here also supports the spectral irradiance variations computed by these models.
Integral field spectroscopy studies based on CALIFA data have recently revealed the presence of ongoing low-level star formation (SF) in the periphery of ~10% of local early-type galaxies (ETGs), witnessing a still ongoing inside-out galaxy growth process. A distinctive property of the nebular component in these ETGs, classified i+, is a two-radial-zone structure, with the inner zone displaying LINER emission with a H\alpha equivalent width EW~1{\AA}, and the outer one (3{\AA}<EW<~20{\AA}) showing HII-region characteristics. Using CALIFA IFS data, we empirically demonstrate that the confinement of nebular emission to the galaxy periphery leads to a strong aperture (or, redshift) bias in spectroscopic single-fiber studies of type i+ ETGs: At low redshift (<~0.45), SDSS spectroscopy is restricted to the inner (SF-devoid LINER) zone, thereby leading to their erroneous classification as "retired" galaxies (systems lacking SF and whose faint emission is powered by pAGB stars). Only at higher z's the SDSS aperture can encompass the outer SF zone, permitting their unbiased classification as "composite SF/LINER". We also demonstrate that the principal effect of a decreasing aperture on the classification of i+ ETGs via standard BPT emission-line ratios consists in a monotonic up-right shift precisely along the upper-right wing of the "seagull" distribution. Motivated by these insights, we also investigate theoretically these biases in aperture-limited studies of inside-out growing galaxies as a function of z. To this end, we devise a simple model, which involves an outwardly propagating SF process, that reproduces the radial extent and two-zone EW distribution of i+ ETGs. By simulating on this model the spectroscopic SDSS aperture, we find that SDSS studies at z<~1 are progressively restricted to the inner LINER-zone, and miss an increasingly large portion of the H\alpha-emitting periphery.
Magnetic fields are considered as a vital ingredient of contemporary star formation, and may have been important during the formation of the first stars in the presence of an efficient amplification mechanism. Initial seed fields are provided via plasma fluctuations, and are subsequently amplified by the small-scale dynamo, leading to a strong tangled magnetic field. Here we explore how the magnetic field provided by the small-scale dynamo is further amplified via the $\alpha-\Omega$ dynamo in a protostellar disk and assess its implications. For this purpose, we consider two characteristic cases, a typical Pop.~III star with $10$~M$_\odot$ and an accretion rate of $10^{-3}$~M$_\odot$~yr$^{-1}$, and a supermassive star with $10^5$~M$_\odot$ and an accretion rate of $10^{-1}$~M$_\odot$~yr$^{-1}$. For the $10$~M$_\odot$ Pop.~III star, we find that coherent magnetic fields can be produced on scales of at least $100$~AU, which are sufficient to drive a jet with a luminosity of $100$~L$_\odot$ and a mass outflow rate of $10^{-3.7}$~M$_\odot$~yr$^{-1}$. For the supermassive star, the dynamical timescales in its environment are even shorter, implying smaller orbital timescales and an efficient magnetization out to at least $1000$~AU. The jet luminosity corresponds to $\sim10^{6.0}$~L$_\odot$, and a mass outflow rate of $10^{-2.1}$~M$_\odot$~yr$^{-1}$. We expect that the feedback from the supermassive star can have a relevant impact on its host galaxy.
Under very general assumptions of metric theory of spacetime, photons traveling along null geodesics and photon number conservation, two observable concepts of cosmic distance, i.e. the angular diameter and the luminosity distances are related to each other by the so called distance duality relation (DDR) $D^L=D^A(1+z)^2$. Observational validation of this relation is quite important because any evidence of its violation could be a signal of new physics. In this letter we introduce a new method to test DDR based on strong gravitational lensing systems and supernovae Ia. Using a new compilation of strong lensing systems and JLA compilation of SNe Ia we found no evidence of DDR violation. However, not so much the final result but the method itself is worth attention, because unlike previously proposed techniques, it does not depend on prior assumptions concerning the details of cosmological model and galaxy cluster modelling.
We report on photometric and spectroscopic observations of white dwarf companions to four binary radio millisecond pulsars, leading to the discovery of companions to PSRs J0614-3329, J1231-1411 and J2017+0603. We place limits on the brightness of the companion to PSR J0613-0200. Optical spectroscopy of the companion to PSR J0614-3329 identifies it as a DA type white dwarf with a temperature of Teff=6460+-80 K, a surface gravity log g=7.0+-0.2 cgs and a mass of Mwd=0.24+-0.04 Msun. We find that the distance to PSR J0614-3329 is smaller than previously estimated, removing the need for the pulsar to have an unrealistically high gamma-ray efficiency. Comparing the photometry with predictions from white dwarf cooling models allows us to estimate temperatures and cooling ages of the companions to PSRs J0613-0200, J1231-1411 and J2017+0603. We find that the white dwarfs in these systems are cool Teff<4000 K and old >5 Gyr. Thin Hydrogen envelopes are required for these white dwarfs to cool to the observed temperatures, and we suggest that besides Hydrogen shell flashes, irradiation driven mass loss by the pulsar may have been important.
We present [C/Fe] and [N/Fe] abundance ratios and CH({\lambda}4300) and S({\lambda}3883) index measurements for 94 red giant branch (RGB) stars in the Sculptor dwarf spheroidal galaxy from VLT/VIMOS MOS observations at a resolving power R= 1150 at 4020 {\AA}. This is the first time that [N/Fe] abundances are derived for a large number of stars in a dwarf spheroidal. We found a trend for the [C/Fe] abundance to decrease with increasing luminosity on the RGB across the whole metallicity range, a phenomenon observed in both field and globular cluster giants, which can be interpreted in the framework of evolutionary mixing of partially processed CNO material. Both our measurements of [C/Fe] and [N/Fe] are in good agreement with the theoretical predictions for stars at similar luminosity and metallicity. We detected a dispersion in the carbon abundance at a given [Fe/H], which cannot be ascribed to measurement uncertainties alone. We interpret this observational evidence as the result of the contribution of different nucleosynthesis sources over time to a not well-mixed interstellar medium. We report the discovery of two new carbon-enhanced, metal-poor stars. These are likely the result of pollution from material enriched by asymptotic giant branch stars, as indicated by our estimates of [Ba/Fe]> +1. We also attempted a search for dissolved globular clusters in the field of the galaxy by looking for the distinctive C-N pattern of second population globular clusters stars in a previously detected, very metal-poor, chemodynamical substructure. We do not detect chemical anomalies among this group of stars. However, small number statistics and limited spatial coverage do not allow us to exclude the hypotheses that this substructure forms part of a tidally shredded globular cluster.
Acceleration of particles and plasma heating is one of the fundamental problems in solar flare physics. An accurate determination of the spectrum of flare energized electrons over a broad energy range is crucial for our understanding of aspects such as the acceleration mechanism and the total flare energy. Recent years have seen a growing interest in the kappa-distribution as representation of the total spectrum of flare accelerated electrons. In this work we present the kappa-distribution as a differential emission measure. This allows for inferring the electron distribution from X-ray observations and EUV observations by simultaneously fitting the proposed function to RHESSI and SDO/AIA data. This yields the spatially integrated electron spectra of a coronal source between less than 0.1 keV up to several tens of keV. The method is applied to a single-loop GOES C4.1 flare. The results show that the total energy can only be determined accurately by combining RHESSI and AIA observations. Simultaneously fitting the proposed representation of the kappa-distribution reduces the electron number density in the analyzed flare by a factor of ~30 and the total flare energy by a factor of ~5 compared with the commonly used fitting of RHESSI spectra. The spatially integrated electron spectrum of the investigated flare between 0.043 keV and 24 keV is consistent with the combination of a low-temperature (~2 MK) component and a hot (~11 MK) kappa-like component with spectral index 4, reminiscent of solar wind distributions.
One of the open problems for AGN is the nature of the primary X-ray emission: it is likely due to Comptonization of soft UV photons, but the optical depth and temperature of the emitting corona were largely unknown before the launch of the Nuclear Spectroscopic Telescope Array (NuSTAR). It is the first focusing hard X-ray telescope on orbit, 100 times more sensitive in the 10-79 keV band compared to previous observatories, enabling the study of AGN at high energies with high precision. We present and discuss the results on the hot corona parameters of Active Galactic Nuclei that have been recently measured with NuSTAR (often in coordination with XMM-Newton, Suzaku or Swift) with unprecedented accuracy, in a number of local Seyfert galaxies.
We investigate signatures that would be produced in the spectrum and sky distribution of UHECR by a population of the Galactic sources of high-energy protons in the energy range around 1 EeV, i.e., around the diffusive-to-ballistic transition. In this regime, the CR flux has to be calculated numerically. We employ the approach that consists in backtracking anti-protons from Earth through the Galaxy and integrating the source emissivity along the trajectory. This approach makes evident two generic features of the transition region: sharp increase of the total flux as the energy decreases across the transition region, and its strong anisotropy (appearance of a bright compact spot) all the way until the onset of the diffusive regime. We then discuss and compare several methods to experimentally detect or constrain these features. We find that a few percent admixture of the Galactic protons can in principle be detected by the current UHECR experiments.
Radial velocity (RV) monitoring of solar-type visual binaries has been conducted at the CTIO/SMARTS 1.5-m telescope to study short-period systems. Data reduction is described, mean and individual RVs of 163 observed objects are given. New spectroscopic binaries are discovered or suspected in 17 objects, for some of them orbital periods could be determined. Subsystems are efficiently detected even in a single observation by double lines and/or by the RV difference between the components of visual binaries. The potential of this detection technique is quantified by simulation and used for statistical assessment of 96 wide binaries within 67pc. It is found that 43 binaries contain at least one subsystem and the occurrence of subsystems is equally probable in either primary or secondary components. The frequency of subsystems and their periods match the simple prescription proposed by the author (2014, AJ, 147, 87). The remaining 53 simple wide binaries with a median projected separation of 1300AU have the distribution of the RV difference between their components that is not compatible with the thermal eccentricity distribution f(e)=2e but rather matches the uniform eccentricity distribution.
Pulsar magnetospheres are shaped by ultra-relativistic electron/positron plasmas flowing in a strong magnetic field and subject to strong gravitational fields. The former induces magnetospheric currents and space charges responsible for the distortion of the electromagnetic field based on pure electrodynamics. The latter induces other perturbations in these fields based on space-time curvature. The force-free approximation describes the response of this magnetosphere to the presence of currents and charges and has been investigated by many authors. In this context, general relativity has been less discussed to quantify its influence on the neutron star electrodynamics. It is the purpose of this paper to compute general-relativistic force-free pulsar magnetospheres for realistic magnetic field configurations such as the inclined dipole. We performed time-dependent simulations of Maxwell equations in the 3+1 formalism of a stationary background metric in the slow-rotation approximation. We computed the resulting Poynting flux depending on the ratio~$R/\rlight$ and on frame-dragging through the spin parameter~$\as$, $R$ is the neutron star radius and $\rlight$ the light-cylinder radius. Both effects act together to increase the total Poynting flux seen by a distant observer by a factor up to~2 depending on the rotation rate. Moreover we retrieve the $\sin^2\chi$ dependence of this luminosity, $\chi$ being the obliquity of the pulsar, as well as a braking index close to $n=3$. We also show that the angular dependence of the Poynting flux scales like $\sin^2\vartheta$ for the aligned rotator but like $\sin^4\vartheta$ for the orthogonal rotator, $\vartheta$ being the colatitude.
Various extensions of the Standard Model motivate the existence of stable
magnetic monopoles that could have been created during an early high-energy
epoch of the Universe. These primordial magnetic monopoles would be gradually
accelerated by cosmic magnetic fields and could reach high velocities that make
them visible in Cherenkov detectors such as IceCube.
Equivalently to electrically charged particles, magnetic monopoles produce
direct and indirect Cherenkov light while traversing through matter at
relativistic velocities.
This paper describes searches for relativistic (v>0.76c) and mildly
relativistic (v>0.51c) monopoles, each using one year of data taken in 2008/09
and 2011/12 respectively. No monopole candidate was detected. For a velocity
above 0.51c the monopole flux is constrained down to a level of 1.55x10^-18
cm-2 s-1 sr-1. This is an improvement of almost two orders of magnitude over
previous limits.
Flux magnification is an interesting complement to shear-based lensing measurements, especially at high redshift where sources are harder to resolve. One measures either changes in the source density (magnification bias) or in the shape of the flux distribution (e.g. magnitude-shift). The interpretation of these measurements relies on theoretical estimates of how the observables change under magnification. Here we present simulations to create multi-band photometric mock catalogues of Lyman-break galaxies in a CFHTLenS-like survey that include several observational effects that can change these relations, making simple theoretical estimates unusable. In particular, we show how the magnification bias can be affected by photometric noise, colour selection, and dust extinction. We find that a simple measurement of the slope of the number-counts is not sufficient for the precise interpretation of virtually all observations of magnification bias. We also explore how sensitive the shift in the mean magnitude of a source sample in different photometric bands is to magnification including the same observational effects. Again we find significant deviations from simple analytical estimates. We also discover a wavelength-dependence of the magnitude-shift effect when applied to a colour-selected noisy source sample. Such an effect can mimic the reddening by dust in the lens. It has to be disentangled from the dust extinction before the magnitude-shift/colour-excess can be used to measure the distribution of either dark matter or extragalactic dust. Using simulations like the ones presented here these observational effects can be studied and eventually removed from observations making precise measurements of flux magnification possible.
Gamma-ray burst sources appear to fulfill all the conditions for being efficient cosmic ray accelerators, and being extremely compact, are also expected to produce multi-GeV to PeV neutrinos. I review the basic model predictions for the expected neutrino fluxes in classical GRBs as well as in low luminosity and choked bursts, discussing the recent IceCube observational constraints and implications from the observed diffuse neutrino flux.
We present a series of high-resolution sunspot simulations that cover a time span of up to 100 hours. The simulation domain extends about 18 Mm in depth beneath the photosphere and 98 Mm horizontally. We use open boundary conditions that do not maintain the initial field structure against decay driven by convective motions. We consider two setups: A sunspot simulation with penumbra, and a "naked-spot" simulation in which we removed the penumbra after 20 hours through a change in the magnetic top boundary condition. While the sunspot has an Evershed outflow of 3-4 km/s, the naked spot is surrounded by an inflow of 1-2 km/s in close proximity. However, both spots are surrounded by an outflow on larger scales with a few 100 m/s flow speed in the photosphere. While the sunspot has almost constant magnetic flux content for the simulated time span of 3-4 days, the naked spot decays steadily at a rate of $10^{21}$ Mx/day. A region with reduced downflow filling factor, which is more extended for the sunspot, surrounds both spots. The absence of downflows perturbs the upflow/downflow massflux balance and leads to a large-scale radially overturning flow system, the photospheric component of this flow is to the observable moat flow. The reduction of the downflow filling factor also inhibits submergence of magnetic field in the proximity of the spots, which stabilizes them against decay. While this effect is present for both spots, it is more pronounced for the sunspot and explains the almost stationary magnetic flux content.
We study the migration of three-planet systems in an irradiated 1+1D $\alpha$-disc with photoevaporation. We performed $2700$ simulations with various planets' masses and initial orbits. We found that most of the systems which ended up as compact configurations form chains of mean motion resonances (MMRs) of the first and higher orders. Most of the systems involved in chains of MMRs are periodic configurations. The period ratios of such system, though, are not necessarily close to exact commensurability. If a given system resides in a divergent migration zone in the disc, the period ratios increase and evolve along resonant divergent migration paths at ($P_2/P_1, P_3/P_2)$-diagram, where $P_1, P_2, P_3$ are the orbital periods of the first, second and third planet, respectively. The observed systems, though, do not lie on those paths. We show that an agreement between the synthetic and the observed systems distributions could be achieved if the orbital circularization was slower than it results from the isothermal disc model.
Kepler-7b is to date the only exoplanet for which clouds have been inferred from the optical phase curve -- from visible-wavelength whole-disk brightness measurements as a function of orbital phase. Added to this, the fact that the phase curve appears dominated by reflected starlight makes this close-in giant planet a unique study case. Here we investigate the information on coverage and optical properties of the planet clouds contained in the measured phase curve. We generate cloud maps of Kepler-7b and use a multiple-scattering approach to create synthetic phase curves, thus connecting postulated clouds with measurements. We show that optical phase curves can help constrain the composition and size of the cloud particles. Indeed, model fitting for Kepler-7b requires poorly absorbing particles that scatter with low-to-moderate anisotropic efficiency, conclusions consistent with condensates of silicates, perovskite, and silica of submicron radii. We also show that we are limited in our ability to pin down the extent and location of the clouds. These considerations are relevant to the interpretation of optical phase curves with general circulation models. Finally, we estimate that the spherical albedo of Kepler-7b over the Kepler passband is in the range 0.4--0.5.
Context. 1E 1740.7-2942 is believed to be one of the two prototypical microquasars towards the Galactic center region whose X-ray states strongly resemble those of Cygnus X-1. Yet, the bipolar radio jets of 1E 1740.7-2942 are very reminiscent of a radio galaxy. The true nature of the object has thus remained an open question for nearly a quarter of a century. Aims. Our main goal here is to confirm the Galactic membership of 1E 1740.7-2942 by searching for morphological changes of its extended radio jets in human timescales. This work was triggered as a result of recent positive detection of fast structural changes in the large-scale jets of its 'twin' GRS 1758-258. Methods. We carried out an in-depth exploration of the VLA public archives and fully recalibrated all 1E 1740.7-2942 extended data sets in the C configuration of the array. We obtained and analyzed matching beam radio maps for five epochs, covering years 1992, 1993, 1994, 1997 and 2000, with an angular resolution of a few arcseconds. Results. We clearly detected structural changes in the arcminute jets of 1E 1740.7-2942 on timescales of roughly a year, which set a firm distance upper limit of 12 kpc. Moreover, a simple precessing model was simultaneously fitted to the five observing epochs available. The observed changes in the jet flow are strongly suggestive of a precession period of ~1.3 years. Conclusions. The fitting of the precession model to the data yields a distance of ~5 kpc. This value, and the observed changes, rule out any remaining doubts about the 1E 1740.7-2942 Galactic nature. To our knowledge, this microquasar is the second whose jet precession ephemeris become available after SS433. This kind of information is relevant to the physics of compact objects, since the genesis of the precession phenomenon occurs very close to the interplay region between the accretion disk and the compact object in the system.
Owing to the paucity of sub-arcsecond (sub)mm observations required to probe the innermost regions of newly forming protostars, several fundamental questions are still being debated, such as the existence and coevality of close multiple systems. We study the physical and chemical properties of the jets and protostellar sources in the NGC1333-IRAS4A proto-binary system using continuum emission and molecular tracers of shocked gas. We observed NGC1333-IRAS4A in the SiO(6-5), SO(6_5-5_4), and CO(2-1) lines and the continuum emission at 1.3, 1.4, and 3 mm using the IRAM Plateau de Bure Interferometer in the framework of the CALYPSO large program. We clearly disentangle for the first time the outflow emission from the two sources A1 and A2. The two protostellar jets have very different properties: the A1 jet is faster, has a short dynamical timescale (<10^3 yr), and is associated with H2 shocked emission, whereas the A2 jet, which dominates the large-scale emission, is associated with diffuse emission, bends, and emits at slower velocities. The observed bending of the A2 jet is consistent with the change of propagation direction observed at large scale and suggests jet precession on very short timescales (~200-600 yr). In addition, a chemically rich spectrum with emission from several COMs (e.g. HCOOH, CH3OCHO, CH3OCH3) is only detected towards A2. Finally, very high-velocity shocked emission (~50 km s^-1) is observed along the A1 jet. An LTE analysis shows that SiO, SO, and H2CO abundances in the gas phase are enhanced up to (3-4)x10^{-7}, (1.4-1.7)x10^{-6}, and (3-7.9)x10^{-7}, respectively. The intrinsic different properties of the jets and driving sources in NGC1333-IRAS4A suggest different evolutionary stages for the two protostars, with A1 being younger than A2, in a very early stage of star formation previous to the hot-corino phase.
Gravitational waves from coalescences of neutron stars or stellar-mass black holes into intermediate-mass black holes (IMBHs) of $\gtrsim 100$ solar masses represent one of the exciting possible sources for advanced gravitational-wave detectors. These sources can provide definitive evidence for the existence of IMBHs, probe globular-cluster dynamics, and potentially serve as tests of general relativity. We analyse the accuracy with which we can measure the masses and spins of the IMBH and its companion in intermediate-mass ratio coalescences. We find that we can identify an IMBH with a mass above $100 ~ M_\odot$ with $95\%$ confidence provided the massive body exceeds $130 ~ M_\odot$. For source masses above $\sim200 ~ M_\odot$, the best measured parameter is the frequency of the quasi-normal ringdown. Consequently, the total mass is measured better than the chirp mass for massive binaries, but the total mass is still partly degenerate with spin, which cannot be accurately measured. Low-frequency detector sensitivity is particularly important for massive sources, since sensitivity to the inspiral phase is critical for measuring the mass of the stellar-mass companion. We show that we can accurately infer source parameters for cosmologically redshifted signals by applying appropriate corrections. We investigate the impact of uncertainty in the model gravitational waveforms and conclude that our main results are likely robust to systematics.
Magnetic reconnection is a leading mechanism for dissipating magnetic energy and accelerating nonthermal particles in Poynting-flux dominated flows. In this letter, we investigate nonthermal particle acceleration during magnetic reconnection in a magnetically-dominated ion-electron plasma using fully kinetic simulations. For an ion-electron plasma with total magnetization $\sigma_0=B^2/(4\pi n(m_i+m_e)c^2)$, the magnetization for each species is $\sigma_i \sim \sigma_0$ and $\sigma_e \sim (m_i/m_e) \sigma_0$, respectively. We have studied the magnetically dominated regime by varying $\sigma_{e} = 10^3 - 10^5$ with initial ion and electron temperatures $T_i = T_e = 5 - 20 m_ec^2$ and mass ratio $m_i/m_e = 1 - 1836$. The results demonstrate that reconnection quickly establishes power-law energy distributions for both electrons and ions within several ($2-3$) light-crossing times. For the cases with periodic boundary conditions, the power-law index is $1<s<2$ for both electrons and ions. The break energies for electrons and ions are $\gamma_e \sim \sigma_e$ and $\gamma_i \sim \sigma_i$, respectively. The main acceleration mechanism is a Fermi-like acceleration through the drift motions of charged particles. When comparing the spectra for electrons and ions in momentum space, the spectral indices $s_p$ are identical as predicted in Fermi acceleration. We also find the bulk flow can carry a significant amount of energy during the simulations. We discuss the implication of this study in the context of Poynting-flux dominated jets and pulsar winds especially the applications for explaining the nonthermal high-energy emissions.
Linear halo bias is the response of dark matter halo number density to a long wavelength fluctuation in the dark matter density. Using abundance matching between separate universe simulations which absorb the latter into a change in the background, we test the consistency relation between the change in a one point function, the halo mass function, and a two point function, the halo-matter cross correlation in the long wavelength limit. We find excellent agreement between the two at the $1-2\%$ level for average halo biases between $1 \lesssim \bar b_1 \lesssim 4$ and no statistically significant deviations at the $4-5\%$ level out to $\bar b_1 \approx 8$. The separate universe technique provides a way of calibrating linear halo bias efficiently for even highly biased rare halos in the $\Lambda$CDM model. Observational violation of the consistency relation would indicate new physics, e.g.~in the dark matter, dark energy or primordial non-Gaussianity sectors.
We study the local response to long wavelength fluctuations in cosmological $N$-body simulations, focusing on the matter and halo power spectra, halo abundance and non-linear transformations of the density field. The long wavelength mode is implemented using an effective curved cosmology and a mapping of time and distances. The method provides an alternative, most probably more precise, way to measure the isotropic halo biases. Limiting ourselves to the linear case, we find generally good agreement between the biases obtained from the curvature method and the traditional power spectrum method at the level of a few percent. We also study the response of halo counts to changes in the variance of the field and find that the slope of the relation between the responses to density and variance differs from the naive derivation assuming a universal mass function by 18%. This has implications for measurements of the amplitude of local non-Gaussianity using scale dependent bias. We also analyze the halo power spectrum and halo-dark matter cross-spectrum response to long wavelength fluctuations and derive second order halo bias from it, as well as the super-sample variance contribution to the galaxy power spectrum covariance matrix.
We estimate the LGRB progenitor rate using our recent work on the effects of environmental metallically on LGRB formation in concert with SNe statistics via an approach patterned loosely off the Drake equation. Beginning with the cosmic star-formation history, we consider the expected number of broad-line Type Ic events (the SNe type associated with LGRBs) that are in low metallicity host environments adjusted by the contribution of high metallicity host environments at a much reduced rate. We then compare this estimate to the observed LGRB rate corrected for instrumental selection effects to provide a combined estimate of the efficiency fraction of these progenitors to produce LGRBs and the fraction of which are beamed in our direction. From this we estimate that an aligned LGRB occurs for approximately every 4000 low metallically broad-lined Type Ic Supernovae. Therefore if one assumes a semi-nominal beaming factor of 100 then only about one such supernova out of 40 produce an LGRB. Finally we propose an off-axis LGRB search strategy of targeting for radio observation broad-line Type Ic events that occur in low metallicity hosts.
We suggest that the energetic radiation from core-collapse super-luminous supernovae (SLSNe) is due to a long lasting accretion process onto the newly born neutron star (NS), resulting from an inefficient operation of the jet-feedback mechanism. The jets that are launched by the accreting NS or black hole (BH) maintain their axis due to a rapidly rotating pre-collapse core, and do not manage to eject core material from near the equatorial plane. The jets are able to eject material from the core along the polar directions, and reduce the gravity near the equatorial plane. The equatorial gas expands, and part of it falls back over a timescale of minutes to days to prolong the jets-launching episode. According to the model for SLSNe proposed in the present paper, the principal parameter that distinguishes between the different cases of CCSN explosions, such as between normal CCSNe and SLSNe, is the efficiency of the jet-feedback mechanism. This efficiency in turn depends on the pre-collapse core mass, envelope mass, core convection, and most of all on the angular momentum profile in the core. One prediction of the inefficient jet-feedback mechanism for SLSNe is the formation of a slow equatorial outflow in the explosion. Typical velocity and mass of this outflow are approximately 1000 km/s and greater than about 1 solar mass, respectively.
We study the $TT\mu$ bispectrum, generated by correlations between Cosmic Microwave Background temperature (T) anisotropies and chemical potential ($\mu$) distortions, and we analyze its dependence on primordial local trispectrum parameters $g_{\rm NL}$ and $\tau_{\rm NL}$. We cross-check our results by comparing the full bispectrum calculation with the expectations from a general physical argument, based on predicting the shape of $\mu$-T correlations from the couplings between short and long perturbation modes induced by primordial non-Gaussianity. We show that $both$ $g_{\rm NL}$ and $\tau_{\rm NL}$-parts of the primordial trispectrum source a non-vanishing $TT\mu$ signal, contrary to the $\mu\mu$ auto-correlation function, which is sensitive only to the $\tau_{\rm NL}$-component. A simple Fisher matrix-based forecast shows that a futuristic, cosmic-variance dominated experiment could in principle determine $g_{\rm NL}$ and $\tau_{\rm NL}$ from $TT\mu$ with $\Delta g_{\rm NL} \simeq 4$, $\Delta \tau_{\rm NL} \simeq 0.02$ sensitivities.
It is often argued that inflation erases all the information about what took place before it started. Quantum gravity, relevant in the Planck era, seems therefore mostly impossible to probe with cosmological observations. In general, only very ad hoc scenarios or hyper fine-tuned initial conditions can lead to observationally testable theories. Here we consider a well-defined and well motivated candidate quantum cosmology model that predicts inflation. Using the most recent observational constraints on the cosmic microwave background B modes, we show that the model is excluded for all its parameter space, without any tuning. Some important consequences are drawn for the deformed algebra approach to loop quantum cosmology. We emphasize that neither loop quantum cosmology in general nor loop quantum gravity are disfavored by this study but their falsifiability is established.
We establish a correspondence between general relativity with diffeomorphism invariance and scalar field theories with Galilean invariance: notions as the Levi-Civita connection and the Riemann tensor have a Galilean counterpart. This suggests Galilean field theories as the unique non-trivial alternative to gauge theories (including general relativity). Moreover, it is shown that the requirement of a first-order Palatini formalism uniquely determines the Galileon models with second-order field equations, similar to the Lovelock gravity theories. Possible extensions are discussed.
While the use of numerical general relativity for modeling astrophysical phenomena and compact objects is commonplace, the application to cosmological scenarios is only just beginning. Here, we examine the expansion of a spacetime using the Baumgarte-Shapiro-Shibata-Nakamura (BSSN) formalism of numerical relativity in synchronous gauge. The universe that emerges exhibits an average Friedmann-Lema\"itre-Robertston-Walker (FLRW) behavior, however this universe also exhibits locally inhomogeneous expansion beyond that expected in linear perturbation theory around a FLRW background. This departure from FLRW is an important path-dependent effect that will need to be considered for precise calculations of physical observables in an inhomogeneous universe.
We present cosmological-scale numerical simulations of an evolving universe in full general relativity (GR) and introduce a new numerical tool, {\sc CosmoGRaPH}, which employs the Baumgarte-Shapiro-Shibata-Nakamura (BSSN) formalism on a 3-dimensional grid. Using {\sc CosmoGRaPH}, we calculate the effect of an inhomogeneous matter distribution on the evolution of a spacetime. We also present the results of a set of standard stability tests to demonstrate the robustness of our simulations.
We study the impact on the Sun of an exotic energy-loss channel caused by plasmon decay into fermionic minicharged particles with charge $\epsilon e$ and mass $m_f$. We compare solar models with this extra emission to helioseismological and neutrino data, obtaining a bound $\epsilon <2\times 10^{-14}\ ({\rm 95\%\, CL})$ for $m_f\lesssim 25 \, \text{eV}$. Our result is competitive with previous limits from the cooling of globular cluster stars, while at the same time it is better understood and takes theoretical and observational errors into account.
In this paper we present a new theory for unification of electromagnetic and gravitational interactions. By considering a four-dimensional spacetime as a hypersurface embedded in a five-dimensional bulk spacetime, we derive the complete set of field equations on the four-dimensional spacetime from the five-dimensional Einstein field equation. We show that, besides the Einstein field equation on the four-dimensional spacetime, a new electromagnetic field equation is also derived: $\nabla_a F^{ab}-\xi R^b_{\;\,a}A^a=-4\pi J^b$ with $\xi=-2$, where $F^{ab}$ is the antisymmetric electromagnetic field tensor defined by the potential vector $A^a$, $R_{ab}$ is the Ricci curvature tensor of the hypersurface, and $J^a$ is the electric current vector. The new electromagnetic field equation differs from the Einstein-Maxwell equation by a curvature-coupled term $\xi R^b_{\;\,a}A^a$, which addresses the problem of incompatibility of the Einstein-Maxwell equation with a universe containing a uniformly distributed net charge as discussed in a previous paper by the author. Hence, the new theory is different from the Kaluza-Klein theory and its variants. In the four-dimensional Einstein field equation derived in the new theory, the source term includes the stress-energy tensor of electromagnetic fields as well as the stress-energy tensor of other unidentified matter. We show that, under some conditions the unidentified matter can be interpreted as a cosmological constant on the four-dimensional spacetime. We argue that, the new electromagnetic field equation and hence the new unified theory can be tested in an environment with a high mass density, e.g., inside a neutron star or a white dwarf, and in the early epoch of the universe.
Possible astrophysical consequences of the Ho\v{r}ava quantum gravity theory have been recently studied by several authors. They usually employ the Kehagias-Sfetsos (KS) spacetime which is a spherically symmetric vacuum solution of a specific version of Ho\v{r}ava's gravity. The KS metric has several unusual geometrical properties that in the present article we examine by means of the often used technique of embedding diagrams. We pay particular attention to the transition between naked singularity and black-hole states, which is possible along some particular sequences of the KS metrics.
We present fully nonlinear and exact cosmological perturbation equations in the presence of multiple components of fluids and minimally coupled scalar fields. We ignore the tensor-type perturbation. The equations are presented without taking the temporal gauge condition in the Friedmann background with general curvature and the cosmological constant. For each fluid component we ignore the anisotropic stress. The multiple component nature, however, introduces the anisotropic stress in the collective fluid quantities. We prove the Newtonian limit of multiple fluids in the zero-shear gauge and the uniform-expansion gauge conditions, present the Newtonian hydrodynamic equations in the presence of general relativistic pressure in the zero-shear gauge, and present the fully nonlinear equations and the third-order perturbation equations of the nonrelativistic pressure fluids in the CDM-comoving gauge.
Within the fluid iron cores of terrestrial planets, convection and the resulting generation of global magnetic fields are controlled by the overlying rocky mantle. The thermal structure of the lower mantle determines how much heat is allowed to escape the core. Hot lower mantle features, such as the thermal footprint of a giant impact or hot mantle plumes, will locally reduce the heat flux through the core mantle boundary (CMB), thereby weakening core convection and affecting the magnetic field generation process. In this study, we numerically investigate how parametrised hot spots at the CMB with arbitrary sizes, amplitudes, and positions affect core convection and hence the dynamo. The effect of the heat flux anomaly is quantified by changes in global flow symmetry properties, such as the emergence of equatorial antisymmetric, axisymmetric (EAA) zonal flows. For purely hydrodynamic models, the EAA symmetry scales almost linearly with the CMB amplitude and size, whereas self-consistent dynamo simulations typically reveal either suppressed or drastically enhanced EAA symmetry depending mainly on the horizontal extent of the heat flux anomaly. Our results suggest that the length scale of the anomaly should be on the same order as the outer core radius to significantly affect flow and field symmetries. As an implication to Mars and in the range of our model, the study concludes that an ancient core field modified by a CMB heat flux anomaly is not able to heterogeneously magnetise the crust to the present-day level of north--south asymmetry on Mars. The resulting magnetic fields obtained using our model either are not asymmetric enough or, when they are asymmetric enough, show rapid polarity inversions, which are incompatible with thick unidirectional magnetisation.
We consider models of chaotic inflation driven by the real parts of a conjugate pair of Higgs superfields involved in the spontaneous breaking of a grand unification symmetry at a scale assuming its Supersymmetric (SUSY) value. We combine a superpotential, which is uniquely determined by applying a continuous R symmetry, with a class of logarithmic or semi-logarithmic Kahler potentials which exhibit a prominent shift-symmetry with a tiny violation, whose strengths are quantified by c- and c+ respectively. The inflationary observables provide an excellent match to the recent Bicep2/Keck Array and Planck results setting 3.5x10^{-3}<=\r+-=\c+/\c-<=1/N where N=3 or 2 is the prefactor of the logarithm. Inflation can be attained for subplanckian inflaton values with the corresponding effective theories retaining the perturbative unitarity up to the Planck scale.
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Low-mass dwarf galaxies are very sensitive test-beds for theories of cosmic structure formation since their weak gravitational fields allow the effects of the relevant physical processes to clearly stand out. Up to now, no unified account exists of the sometimes seemingly conflicting properties of the faintest isolated dwarfs in and around the Local Group, such as Leo T and the recently discovered Leo P and Pisces A systems. Using new numerical simulations, we show that this serious challenge to our understanding of galaxy formation can be effectively resolved by taking into account the regulating influence of the ultraviolet radiation of the first population of stars on a dwarf's star formation rate while otherwise staying within the standard cosmological paradigm for structure formation. These simulations produce faint, gas-dominated, star-forming dwarf galaxies that lie on the baryonic Tully-Fisher relation and that successfully reproduce a broad range of chemical, kinematical, and structural observables of real late-type dwarf galaxies. Furthermore, we stress the importance of obtaining properties of simulated galaxies in a manner as close as possible to the typically employed observational techniques.
A significant fraction of the envelope of low- and intermediate-mass stars is unstable to convection, leading to sub-surface turbulent motion. Here, we consider and include the effects of turbulence pressure in our stellar evolution calculations. In search of an observational signature, we compare the fractional contribution of turbulent pressure to the observed macroturbulent velocities in stars at different evolutionary stages. We find a strong correlation between the two quantities, similar to what was previously found for massive OB stars. We therefore argue that turbulent pressure fluctuations of finite amplitude may excite high-order, high-angular degree stellar oscillations, which manifest themselves at the surface an additional broadening of the spectral lines, i.e., macroturbulence, across most of the HR diagram. When considering the locations in the HR diagram where we expect high-order oscillations to be excited by stochastic turbulent pressure fluctuations, we find a close match with the observational $\gamma$ Doradus instability strip, which indeed contains high-order, non-radial pulsators. We suggest that turbulent pressure fluctuations on a percentual level may contribute to the $\gamma$ Dor phenomenon, calling for more detailed theoretical modelling in this direction.
Type Ia supernovae are heavily used tools in precision cosmology, yet we still are not certain what the progenitor systems are. General plausibility arguments suggest there is potential for identifying double degenerate Type Ia supernova progenitors in intermediate-age open star clusters. We present time-resolved high-resolution spectroscopy of two white dwarfs in the field of the open cluster NGC 6633 that had previously been identified as candidate double degenerates in the cluster. However, three hours of continuous observations of each candidate failed to detect any significant radial velocity variations at the > 10 km/s level, making it highly unlikely that either white dwarf is a double degenerate that will merge within a Hubble Time. The white dwarf LAWDS NGC 6633 4 has a radial velocity inconsistent with cluster membership at the 2.5 sigma level, while the radial velocity of LAWDS NGC 6633 7 is consistent with cluster membership. We conservatively conclude that LAWDS 7 is a viable massive double degenerate candidate, though unlikely to be a Type Ia progenitor. Astrometric data from GAIA will likely be needed to determine if either white dwarf is truly a cluster member.
We present a comprehensive chemical abundance analysis of five red giants and two horizontal branch (HB) stars towards the southern Galactic bulge, at (l,b)$\sim$(0$^{\rm o}$,-11$^{\rm o}$). Based on high-resolution spectroscopy obtained with the Magellan/MIKE spectrograph, we derived up to 23 chemical element abundances and identify a mixed bag of stars, representing various populations in the central regions of the Galaxy. Although cosmological simulations predict that the inner Galaxy was host to the first stars in the Universe, we see no chemical evidence of the ensuing massive supernova explosions: all of our targets exhibit halo-like, solar [Sc/Fe] ratios, which is in contrast to the low values predicted from Population III nucleosynthesis. One of the targets is a CEMP-s star at [Fe/H]=-2.52 dex, and another one is a moderately metal-poor ([Fe/H]=-1.53 dex) CH star with strong enrichment in s-process elements (e.g., [Ba/Fe]=1.35). These individuals provide the first contenders of these classes of stars towards the bulge. Four of the carbon-normal stars exhibit abundance patterns reminiscent of halo star across a metallicity range spanning -2.0 to -2.6 dex, i.e., enhanced $\alpha$-elements and solar Fe-peak and n-capture elements, and the remaining one is a regular metal-rich bulge giant. The position, distance, and radial velocity of one of the metal-poor HB stars coincides with the old trailing arm of the disrupted Sagittarius dwarf galaxy. While their uncertain proper motions prohibit a clear kinematic separation, the stars' abundances and distances suggest that these metal-poor candidates, albeit located towards the bulge, are not of the bulge, but rather inner halo stars on orbits that make them pass through the central regions. Thus, we caution similar claims of detections of metal-poor stars as true habitants of the bulge. (Abridged)
Planets larger than Earth and smaller than Neptune are some of the most numerous in the galaxy, but observational efforts to understand this population have proved challenging because optically thick clouds or hazes at high altitudes obscure molecular features (Kreidberg et al. 2014b). We present models of super Earths that include thick clouds and hazes and predict their transmission, thermal emission, and reflected light spectra. Very thick, lofted clouds of salts or sulfides in high metallicity (1000x solar) atmospheres create featureless transmission spectra in the near-infrared. Photochemical hazes with a range of particle sizes also create featureless transmission spectra at lower metallicities. Cloudy thermal emission spectra have muted features more like blackbodies, and hazy thermal emission spectra have emission features caused by an inversion layer at altitudes where the haze forms. Close analysis of reflected light from warm (~400-800 K) planets can distinguish cloudy spectra, which have moderate albedos (0.05-0.20), from hazy models, which are very dark (0.0-0.03). Reflected light spectra of cold planets (~200 K) accessible to a space-based visible light coronagraph will have high albedos and large molecular features that will allow them to be more easily characterized than the warmer transiting planets. We suggest a number of complementary observations to characterize this population of planets, including transmission spectra of hot (>1000 K) targets, thermal emission spectra of warm targets using the James Webb Space Telescope (JWST), high spectral resolution (R~10^5) observations of cloudy targets, and reflected light spectral observations of directly-imaged cold targets. Despite the dearth of features observed in super Earth transmission spectra to date, different observations will provide rich diagnostics of their atmospheres.
We test the imprint of f(R) modified gravity on the halo mass function, using N-body simulations and a theoretical model developed in (Kopp et al. 2013). We find a very good agreement between theory and simulations. We extend the theoretical model to the conditional mass function and apply it to the prediction of the linear halo bias in f(R) gravity. Using the halo model we obtain a prediction for the non-linear matter power spectrum accurate to ~10% at z=0 and up to k=2h/Mpc. We also study halo profiles for the f(R) models and find a deviation from the standard general relativity result up to 40%, depending on the halo masses and redshift. This has not been pointed out in previous analysis. Finally we study the number density and profiles of voids identified in these f(R) N-body simulations. We underline the effect of the bias and the sampling to identify voids. We find significant deviation from GR when measuring the f(R) void profiles with fR0<-10^{-6}.
We present a statistical analysis of the environments of 11 supernovae (SNe) which occurred in 6 nearby galaxies (z $\lesssim$ 0.016). All galaxies were observed with MUSE, the high spatial resolution integral field spectrograph mounted to the 8m VLT UT4. These data enable us to map the full spatial extent of host galaxies up to $\sim$3 effective radii. In this way, not only can one characterise the specific host environment of each SN, one can compare their properties with stellar populations within the full range of other environments within the host. We present a method that consists of selecting all HII regions found within host galaxies from 2D extinction-corrected H$\alpha$ emission maps. These regions are then characterised in terms of their H$\alpha$ equivalent widths, star formation rates, and oxygen abundances. Identifying HII regions spatially coincident with SN explosion sites, we are thus able to determine where within the distributions of host galaxy e.g. metallicities and ages each SN is found, thus providing new constraints on SN progenitor properties. This initial pilot study using MUSE opens the way for a revolution in SN environment studies where we are now able to study multiple environment SN progenitor dependencies using a single instrument and single pointing.
Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), one of three core programs in the Sloan Digital Sky Survey-IV (SDSS-IV), is an integral-field spectroscopic (IFS) survey of roughly 10,000 nearby galaxies. It employs dithered observations using 17 hexagonal bundles of 2 arcsec fibers to obtain resolved spectroscopy over a wide wavelength range of 3,600-10,300A. To map the internal variations within each galaxy, we need to perform accurate {\it spectral surface photometry}, which is to calibrate the specific intensity at every spatial location sampled by each individual aperture element of the integral field unit. The calibration must correct only for the flux loss due to atmospheric throughput and the instrument response, but not for losses due to the finite geometry of the fiber aperture. This requires the use of standard star measurements to strictly separate these two flux loss factors (throughput versus geometry), a difficult challenge with standard single-fiber spectroscopy techniques due to various practical limitations. Therefore, we developed a technique for spectral surface photometry using multiple small fiber-bundles targeting standard stars simultaneously with galaxy observations. We discuss the principles of our approach and how they compare to previous efforts, and we demonstrate the precision and accuracy achieved. MaNGA's relative calibration between the wavelengths of H$\alpha$ and H$\beta$ has a root-mean-square (RMS) of 1.7%, while that between [NII] $\lambda$6583A and [OII] $\lambda$3727A has an RMS of 4.7%. Using extinction-corrected star formation rates and gas-phase metallicities as an illustration, this level of precision guarantees that flux calibration errors will be sub-dominant when estimating these quantities. The absolute calibration is better than 5% for more than 89% of MaNGA's wavelength range.
We report on the serendipitous discovery of a star-forming galaxy at redshift z=0.116 with morphological features that indicate an ongoing merger. This object exhibits two clearly separated components with significantly different colors, plus a possible tidal stream. Follow-up spectroscopy of the bluer component revealed a low star-forming activity of 0.09 M$_{\odot}$/year and a high metallicity of 12+log(O/H)=8.6. Based on comparison with mass-star-formation-rate and mass-metallicity relations, and on fitting of spectral energy distributions, we obtain a stellar mass of 3x10$^9$ M$_{\odot}$, which renders this object comparable to the Large Magellanic Cloud (LMC). Thus our finding provides a further piece of evidence of a major merger already acting on small, dwarf galaxy-like scales.
Dynamical mass calculations have suggested that the Milky Way globular cluster NGC 6535 belongs to a population of clusters with high mass-to-light ratios, possibly due to a bottom-heavy stellar initial mass function. We use published Hubble Space Telescope data to measure the present day stellar mass function of this cluster within its half-light radius and instead find that it is bottom-light, exacerbating the discrepancy between the dynamical measurement and its known stellar content. The cluster's proximity to the Milky Way bulge and its relatively strong velocity anisotropy are both reasons to be suspicious of the dynamical mass measurement, but we find that neither straightforwardly explains the sense and magnitude of the discrepancy. Although there are alternative potential explanations for the high mass-to-light ratio, such as the presence of large numbers of stellar remnants or dark matter, we find this cluster to be sufficiently perplexing that we now exclude it from a discussion of possible variations in the initial mass function. Because this was the sole known old, Milky Way cluster in the population of high dynamical mass-to-light ratio clusters, some possible explanations for the difference in cluster properties are again open for consideration.
We use a set of high-resolution N-body simulations of the Galactic disk to study its interactions with the population of satellites predicted cosmologically. One simulation illustrates that multiple passages of massive satellites with different velocities through the disk generate a wobble, having the appearance of rings in face-on projections of the stellar disk. They also produce flares in the disk outer parts and gradually heat the disk through bending waves. A different numerical experiment shows that an individual satellite as massive as the Sagittarius dwarf galaxy passing through the disk will drive coupled horizontal and vertical oscillations of stars in underdense regions, with no significant associated heating. This experiment shows that vertical excursions of stars in these low-density regions can exceed 1 kpc in the Solar neighborhood, resembling the coherent vertical oscillations recently detected locally. They can also induce non-zero vertical streaming motions as large as 10-20 km s$^{-1}$, consistent with recent observations in the Galactic disk. This phenomenon appears as a local ring, with no associated disk heating.
A key physical quantity during reionization is the size of HII regions. Previous studies found a characteristic bubble size which increases rapidly during reionization, with apparent agreement between simulations and analytic excursion set theory. Using four different methods, we critically examine this claim. In particular, we introduce the use of the watershed algorithm -- widely used for void finding in galaxy surveys -- which we show to be an unbiased method with the lowest dispersion and best performance on Monte-Carlo realizations of a known bubble size PDF. We find that a friends-of-friends algorithm declares most of the ionized volume to be occupied by a network of volume-filling regions connected by narrow tunnels. For methods tuned to detect those volume-filling regions, previous apparent agreement between simulations and theory is spurious, and due to a failure to correctly account for the window function of measurement schemes. The discrepancy is already obvious from visual inspection. Instead, HII regions in simulations are significantly larger (by factors of 10-1000 in volume) than analytic predictions. The size PDF is narrower, and evolves more slowly with time, than predicted. It becomes more sharply peaked as reionization progresses. These effects are likely caused by bubble mergers, which are inadequately modeled by analytic theory. Our results have important consequences for high-redshift 21cm observations, the mean free path of ionizing photons, and the visibility of Ly-alpha emitters, and point to a fundamental failure in our understanding of the characteristic scales of the reionization process.
An important factor limiting our ability to understand the production and propagation of cosmic rays pertains to the effects of heliospheric forces, commonly known as solar modulation. The solar wind is capable of generating time and charge-dependent effects on the spectrum and intensity of low energy ($\lsim$ 10 GeV) cosmic rays reaching Earth. Previous analytic treatments of solar modulation have utilized the force-field approximation, in which a simple potential is adopted whose amplitude is selected to best fit the cosmic-ray data taken over a given period of time. Making use of recently available cosmic-ray data from the Voyager 1 spacecraft, along with measurements of the heliospheric magnetic field and solar wind, we construct a time, charge and rigidity-dependent model of solar modulation that can be directly compared to data from a variety of cosmic-ray experiments. We provide a simple analytic formula that can be easily utilized in a variety of applications, allowing us to better predict the effects of solar modulation and reduce the number of free parameters involved in cosmic ray propagation models.
We perform dry merger simulations to investigate the role of dry mergers in the size growth of early-type galaxies in high density environments. We replace the virialized dark matter haloes obtained by a large cosmological $N$-body simulation with $N$-body galaxy models consisting of two components, a stellar bulge and a dark matter halo, which have higher mass resolution than the cosmological simulation. We then re-simulate nine cluster forming regions, whose masses range from 1e+14 Msun to 5e+14 Msun. Masses and sizes of stellar bulges are also assumed to satisfy the stellar mass--size relation of high-z compact massive early-type galaxies. We find that dry major mergers considerably contribute to the mass and size growth of central massive galaxies. One or two dry major mergers double the average stellar mass and quadruple the average size between $z=2$ and $z=0$. These growths favorably agree with observations. Moreover, the density distributions of our simulated central massive galaxies grow from the inside-out, which is consistent with recent observations. The mass--size evolution is approximated as R propto M_{*}^{alpha}, with alpha ~ 2.24. Most of our simulated galaxies are efficiently grown by dry mergers, and their stellar mass--size relations match the ones observed in the local Universe. Our results show that the central galaxies in the cluster haloes are potential descendants of high-z (z ~ 2-3) compact massive early-type galaxies. This conclusion is consistent with previous numerical studies which investigate the formation and evolution of compact massive early-type galaxies.
The optical light curve of the quasar PG 1302-102 at $z = 0.278$ shows a strong, smooth 5.2 yr periodic signal, detectable over a period of $\sim 20$ yr. Although the interpretation of this phenomenon is still uncertain, the most plausible mechanisms involve a binary system of two supermassive black holes with a subparsec separation. At this close separation, the nuclear black holes in PG 1302-102 will likely merge within $\sim 10^{5}$ yr due to gravitational wave emission alone. Here we report the rest-frame near-infrared time lags for PG 1302-102. Compiling data from {\it WISE} and {\it Akari}, we confirm that the periodic behavior reported in the optical light curve from Graham et al. (2015) is reproduced at infrared wavelengths, with best-fit observed-frame 3.4 and $4.6 \mu$m time lags of $(2219 \pm 153, 2408 \pm 148)$ days for a near face-on orientation of the torus, or $(4103\pm 153, 4292 \pm 148)$ days for an inclined system with relativistic Doppler boosting in effect. The periodicity in the infrared light curves and the light-travel time of the accretion disk photons to reach the dust glowing regions support that a source within the accretion disk is responsible for the optical variability of PG 1302-102, echoed at the further out dusty regions. The implied distance of this dusty, assumed toroidal region is $\sim$ 1.5 pc for a near face-on geometry, or $\sim$1.1 pc for the relativistic Doppler boosted case.
We present a study of stellar populations in a sample of spectroscopically-confirmed Lyman-break galaxies (LBGs) and Ly$\alpha$ emitters (LAEs) at $5.7<z<7$. These galaxies have deep optical and infrared images from Subaru, $HST$, and $Spitzer$/IRAC. We focus on a subset of 27 galaxies with IRAC detections, and characterize their stellar populations utilizing galaxy synthesis models based on the multi-band data and secure redshifts. By incorporating nebular emission estimated from the observed Ly$\alpha$ flux, we are able to break the strong degeneracy of model spectra between young galaxies with prominent nebular emission and older galaxies with strong Balmer breaks. The results show that our galaxies cover a wide range of ages from several to a few hundred million years (Myr), and a wide range of stellar masses from $\sim10^8$ to $\sim10^{11}$ $M_{\odot}$. These galaxies can be roughly divided into an `old' subsample and a `young' subsample. The `old' subsample consists of galaxies older than 100 Myr, with stellar masses higher than $10^9$ $M_{\odot}$. The galaxies in the `young' subsample are younger than $\sim$30 Myr, with masses ranging between $\sim10^8$ and $\sim3\times10^9$ $M_{\odot}$. Both subsamples display a correlation between stellar mass and star-formation rate (SFR), but with very different normalizations. The average specific SFR (sSFR) of the `old' subsample is 3--4 Gyr$^{-1}$, consistent with previous studies of `normal' star-forming galaxies at $z\ge6$. The average sSFR of the `young' subsample is an order of magnitude higher, likely due to starburst activity. Our results also indicate little or no dust extinction in the majority of the galaxies, as already suggested by their steep rest-frame UV slopes. Finally, LAEs and LBGs with strong Ly$\alpha$ emission are indistinguishable in terms of age, stellar mass, and SFR.
We present the first attempt at a reverberation mapping (RM) experiment that combines broad and intermediate-band photometry, targeting a sample of 13 quasars at $0.2<z<0.9$. The quasars were selected to have strong H$\alpha$ or H$\beta$ emission lines that are located in one of three intermediate bands (with FWHM around 200 \AA) centered at 8045, 8505, and 9171 \AA. The imaging observations were carried out in the intermediate bands and the broad $i$ and $z$ bands using the prime-focus imager 90Prime on the 2.3m Bok telescope. Because of the large ($\sim$1 deg$^2$) field-of-view (FoV) of 90Prime, we were able to include the 13 quasars within only five telescope pointings or fields. The five fields were repeatedly observed over 20-30 epochs that were unevenly distributed over a duration of 5-6 months. The combination of the broad- and intermediate-band photometry allows us to derive accurate light curves for both optical continuum (from the accretion disk) and line (from the broad-line region, or BLR) emission. We detect time lags between the continuum and line emission in 6 quasars. These quasars are at a relatively low redshift range $0.2<z<0.4$. The measured lags are consistent with the current BLR size-luminosity relation for H$\beta$ at $z<0.3$. We demonstrate that by using a small telescope with a large FoV, intermediate-band photometric RM can be efficiently executed for a large sample of quasars at $z>0.2$.
The reionization of intergalactic hydrogen has received intense theoretical scrutiny over the past two decades. Here, we approach the process formally as a percolation process and phase transition. Using semi-numeric simulations, we demonstrate that an infinitely-large ionized region abruptly appears at an ionized fraction of ~0.1 and quickly grows to encompass most of the ionized gas: by an ionized fraction of 0.3, nearly ninety percent of the ionized material is part of this region. Throughout most of reionization, nearly all of the intergalactic medium is divided into just two regions, one ionized and one neutral, and both infinite in extent. We also show that the discrete ionized regions that exist before and near this transition point follow a near-power law distribution in volume, with equal contributions to the total filling factor per logarithmic interval in size up to a sharp cutoff in volume. These qualities are generic to percolation processes, with the detailed behavior a result of long-range correlations in the underlying density field. These insights will be crucial to understanding the distribution of ionized and neutral gas during reionization and provide precise meaning to the intuitive description of reionization as an "overlap" process.
The steep spectrum of neutrinos measured by IceCube extending from >1 PeV down to ~10 TeV has an energy flux now encroaching on the Fermi isotropic GeV background. We examine several implications starting from source energetics requirements for neutrino production. We show how the environment of extragalactic nuclei can extinguish ~10-100 TeV gamma rays and convert their energy to X-rays for plausible conditions of infrared luminosity and magnetic field, so that the Fermi background is not overwhelmed by cascades. We address a variety of scenarios, such as for acceleration by supermassive black holes and hadronic scenarios, and observations that may help elucidate the neutrinos' shadowy origins.
A crucial aspect of understanding planet formation is determining the binarity of the host stars. Results from radial velocity surveys and the follow-up of Kepler exoplanet candidates have demonstrated that stellar binarity certainly does not exclude the presence of planets in stable orbits and the configuration may in fact be relatively common. Here we present new results for the 30 Arietis system which confirms that the B component hosts both planetary and stellar companions. Keck AO imaging provides direct detection of the stellar companion and additional radial velocity data are consistent with an orbiting star. We present a revised orbit of the known planet along with photometry during predicted transit times. Finally, we provide constraints on the properties of the stellar companion based on orbital stability considerations.
We consider turbulent synchrotron emitting media that also exhibits Faraday rotation and provide a statistical description of synchrotron polarization fluctuations. In particular, we consider these fluctuations as a function of the spatial separation of the direction of measurements and as a function of wavelength for the same line-of-sight. On the basis of our general analytical approach, we introduce several measures that can be used to obtain the spectral slopes and correlation scales of both the underlying magnetic turbulence responsible for emission and the spectrum of the Faraday rotation fluctuations. We show the synergetic nature of these measures and discuss how the study can be performed using sparsely sampled interferometric data. We also discuss how additional characteristics of turbulence can be obtained, including the turbulence anisotropy, the three dimensional direction of the mean magnetic field. We consider both cases when the synchrotron emission and Faraday rotation regions coincide and when they are spatially separated. Appealing to our earlier study in Lazarian \& Pogosyan (2012) we explain that our new results are applicable to a wide range of spectral indexes of relativistic electrons responsible for synchrotron emission. We expect wide application of our techniques both with existing synchrotron data sets as well as with big forthcoming data sets from LOFAR and SKA.
As part of a reorganization of the International Astronomical Union (IAU), Commission 4 (Ephemerides) went out of existence after the IAU General Assembly in August 2015. This paper presents brief discussions of some of the developments in fundamental astronomy that have influenced and been influenced by the work of Commission 4 over its 96-year history. The paper also presents notes about some of the publications of the national institutions that have played an essential role in the commission's mission. The contents of this paper were submitted for Commission 4's final report, to appear in IAU Transactions Vol. XXIX-A.
We have examined the more than 1100 drawings of the solar disk made by the German astronomy amateur Johann Caspar Staudach during 1749-1799 and counted the spots on each image. Using the modern perception of how to group spots into active regions we regrouped the spots as a modern observer would. The resulting number of groups was found to be on average 25% higher than the first count of groups performed by Wolf in 1857, and used by Hoyt and Schatten in their construction of the Group Sunspot Number. Compared to other observers at the time, Staudach's drawings have a very low average number, ~2, of spots per group, possibly indicating an inferior telescope likely suffering from spherical and chromatic aberration as would typical of amateur telescopes of the day. We have initiated an ongoing project aiming at observing sunspots with antique telescopes having similar defects in order to determine the factor necessary to bring the Staudach observations onto a modern scale.
The extragalactic background light is expected to be comprised of the cumulative radiation from all galaxies and active galactic nuclei over the cosmic history. In addition to point sources, EBL also contains information from diffuse sources of radiation. An example is the intra-halo light, associated with diffuse stars in dark matter halos resulting from galaxy mergers and tidal interactions, identified based on measurements involving the angular power spectrum of infrared background anisotropies. The angular power spectra of the near-infrared intensities could still contain additional signals and a complete understanding of the nature of the IR background is still lacking in the literature. Here we explore the constraints that can be placed on the decay products associated with particle decays, especially candidate dark matter models involving axions that trace dark matter halos of galaxies. Axions with a mass around a few eV will decay via two photons with wavelengths in the near-IR band, and will leave a signature in the IR background intensity power spectrum. Using recent power spectra measurements from the Hubble Space Telescope (HST) and Cosmic Infrared Background Experiment (CIBER), we find that the 0.6 to 1.6 micron power spectra can be explained with an axion mass of around 4 eV and a total axion abundance as a fractional energy density Omega_a~0.05. Such an abundance is comparable to the baryon density of the Universe. The absolute EBL intensity of axion decay photons is slightly below 1 nW m^-2 sr^-1 at near-IR wavelengths, roughly a factor of 10 to 20 below the total integrated light from galaxies. The suggested axion mass and abundance are not ruled out by existing cosmological observations.
Using a sample of ~410 000 galaxies to depth I_AB = 24 over 8.26 deg^2 in the Bootes field (~10 times larger than z~1 luminosity function studies in the prior literature), we have accurately measured the evolving B-band luminosity function of red galaxies at z<1.2 and blue galaxies at z<1.0. In addition to the large sample size, we utilise photometry that accounts for the varying angular sizes of galaxies, photometric redshifts verified with spectroscopy, and absolute magnitudes that should have very small random and systematic errors. Our results are consistent with the migration of galaxies from the blue cloud to the red sequence as they cease to form stars, and with downsizing in which more massive and luminous blue galaxies cease star formation earlier than fainter less massive ones. Comparing the observed fading of red galaxies with that to be expected from passive evolution alone, we find that the stellar mass contained within the red galaxy population has increased by a factor of ~3.6 from z~1.1 to z~0.1. The bright end of the red galaxy luminosity function fades with decreasing redshift, the rate of fading increasing from ~0.2 mag per unit redshift at z = 1.0 to ~0.8 at z = 0.2. The overall decrease in luminosity implies that the stellar mass in individual highly luminous red galaxies increased by a factor of ~2.2 from z = 1.1 to z = 0.1.
The central engine and jet composition of gamma-ray bursts (GRBs) remain mysterious. Here we suggest that observations on polarization evolution of early optical afterglows may shed light on these questions. We first study the dynamics of a reverse shock and a forward shock that are generated during the interaction of a relativistic jet and its ambient medium. The jet is likely magnetized with a globally large-scale magnetic field from the central engine. The existence of the reverse shock requires that the magnetization degree of the jet should not be high ($\sigma\leq 1$), so that the jet is mainly composed of baryons and leptons. We then calculate the light curve and polarization evolution of an early optical afterglow, and find that when the polarization position angle changes by $90^\circ$ during the early afterglow, the polarization degree is zero for a toroidal magnetic field but is very likely to be non-zero for an aligned magnetic field. This result would be expected to provide a probe for the central engine of GRBs, because an aligned field configuration could originate from a magnetar central engine and a toroidal field configuration could be produced from a black hole via the Blandford-Znajek mechanism. Finally, for such two kinds of magnetic field configurations, we fit the observed data of the early optical afterglow of GRB 120308A equally well.
Recent studies suggest that faint active galactic nuclei may be responsible for the reionization of the universe. Confirmation of this scenario requires spectroscopic identification of faint quasars ($M_{1450}>-24$ mag) at $z \gtrsim6$, but only a very small number of such quasars have been spectroscopically identified so far. Here, we report the discovery of a faint quasar IMS J220417.92+011144.8 at z~6 in a 12.5 deg$^{2}$ region of the SA22 field of the Infrared Medium-deep Survey (IMS). The spectrum of the quasar shows a sharp break at $\sim8443~\rm{\AA}$, with emission lines redshifted to $z=5.944 \pm 0.002$ and rest-frame ultraviolet continuum magnitude $M_{1450}=-23.59\pm0.10$ AB mag. The discovery of IMS J220417.92+011144.8 is consistent with the expected number of quasars at z~6 estimated from quasar luminosity functions based on previous observations of spectroscopically identified low-luminosity quasars . This suggests that the number of $M_{1450}\sim-23$ mag quasars at z~6 may not be high enough to fully account for the reionization of the universe. In addition, our study demonstrates that faint quasars in the early universe can be identified effectively with a moderately wide and deep near-infrared survey such as the IMS.
Active galactic nuclei (AGN) are believed to be promising candidates of extragalactic cosmic-ray accelerators and sources, and associated high-energy neutrino and hadronic gamma-ray emission has been studied for many years. We review models of high-energy neutrino production in AGN, and discuss their implications for the latest IceCube observation of the diffuse neutrino intensity.
In this work, we investigate the molecular gas and star formation properties in the barred spiral galaxy NGC 6946 using multiple molecular lines and star formation tracers. High-resolution image (100 pc) of $^{13}$CO (1-0) is created by single dish NRO45 and interferometer CARMA for the inner 2 kpc disk, which includes the central region (nuclear ring and bar) and the offset ridges of the primary bar. Single dish HCN (1-0) observations were also made to constrain the amount of dense gas. Physical properties of molecular gas are inferred by (1) the Large Velocity Gradient (LVG) calculations using our observations and archival $^{12}$CO (1-0), $^{12}$CO(2-1) data, (2) dense gas fraction suggested by HCN to $^{12}$CO (1-0) luminosity ratio, and (3) infrared color. The results show that the molecular gas in the central region is warmer and denser than that of the offset ridges. Dense gas fraction of the central region is similar with that of LIRGs/ULIRGs, while the offset ridges are close to the global average of normal galaxies. The coolest and least dense region is found in a spiral-like structure, which was misunderstood to be part of the southern primary bar in previous low-resolution observations. Star formation efficiency (SFE) changes by ~ 5 times in the inner disk. The variation of SFE agrees with the prediction in terms of star formation regulated by galactic bar. We find a consistency between star-forming region and the temperature inferred by the infrared color, suggesting that the distribution of sub-kpc scale temperature is driven by star formation.
Using the multi-wavelength images and the photospheric magnetograms from the \emph{Solar Dynamics Observatory}, we study the flare which was associated by the only one coronal mass ejection (CME) in active region (AR) 12192. The eruption of a filament caused a blowout jet, and then an M4.0 class flare occurred. This flare was located at the edge of AR instead of in the core region. The flare was close to the apparently "open" fields, appearing as extreme-ultraviolet structures that fan out rapidly. Due to the interaction between flare materials and "open" fields, the flare became an eruptive flare, leading to the CME. Then at the same site of the first eruption, another small filament erupted. With the high spatial and temporal resolution H$\alpha$ data from the New Vacuum Solar Telescope at the \emph{Fuxian Solar Observatory}, we investigate the interaction between the second filament and the nearby "open" lines. The filament reconnected with the "open" lines, forming a new system. To our knowledge, the detailed process of this kind of interaction is reported for the first time. Then the new system rotated due to the untwisting motion of the filament, implying that the twist was transferred from the closed filament system to the "open" system. In addition, the twist seemed to propagate from the lower atmosphere to the upper layers, and was eventually spread by the CME to the interplanetary space.
A magnetic flux rope structure is believed to exist in most coronal mass ejections (CMEs). However, it has been long debated whether the flux rope exists before eruption or is formed during eruption via magnetic reconnection. The controversy has been continuing because of our lack of routine measurements of the magnetic field in the pre-eruption structure, such as solar filaments. However, recently an indirect method was proposed to infer the magnetic field configuration based on the sign of helicity and the bearing direction of the filament barbs. In this paper, we apply this method to two erupting filament events, one on 2014 September 2 and the other on 2011 March 7, and find that the first filament is supported by a magnetic flux rope and the second filament is supported by a sheared arcade, i.e., the first one is an inverse-polarity filament and the second one is a normal-polarity filament. With the identification of the magnetic configurations in these two filaments, we stress that a flux rope is not a necessary condition for the pre-CME structure.
We report on a search for the presence of signals from extraterrestrial intelligence in the direction of the star system KIC 8462852. Observations were made at radio frequencies between 1-10 GHz using the Allen Telescope Array. No narrowband radio signals were found at a level of 180-300 Jy in a 1 Hz channel, or wideband signals above 100 Jy in a 100 kHz channel.
Newly born and young radio sources are in a delicate phase of their life. Their jets are fighting their way through the surrounding gaseous medium, strongly experiencing this interaction while, at the same time, impacting and affecting the interstellar medium (ISM). Here we present the results from two studies of HI (in absorption) and molecular gas illustrating what can be learned from these phases of the gas. We first describe a statistical study with the WSRT. The study shows that the young radio sources not only have an higher detection rate of HI, but also systematically broader and more asymmetric HI profiles, most of them blueshifted. This supports the idea that we are looking at young radio jets making their way through the surrounding ISM, which also appears to be, on average, richer in gas than in evolved radio sources. Signatures of the impact of the jet are seen in the kinematics of the gas. However, even among the young sources, we identify a population that remains undetected in HI even after stacking their profiles. Orientation effects can only partly explain the result. These objects either are genuinely gas-poor or have different conditions of the medium, e.g. higher spin temperature. We further present the ALMA study of molecular gas in IC5063 to trace in detail the jet impacting the ISM. The kinematics of the cold, molecular gas co-spatial with the radio plasma shows this process in action. The ALMA data reveal a fast outflow of molecular gas extending along the entire radio jet (~1 kpc), with the highest outflow velocities at the location of the brighter hot-spot. We propose a scenario where the radio jet is expanding into a clumpy medium, interacting directly with the clouds and inflating a cocoon that drives a lateral outflow into the ISM.
We present results of long-term multi-wavelength polarization observations of the powerful blazar 3C~279 after its $\gamma$-ray flare on 2013~December 20. We followed up this flare with single-dish polarization observations using two 21-m telescopes of the Korean VLBI Network. Observations carried out weekly from 2013~December~25 to 2015~January~11, at 22~GHz, 43~GHz, 86~GHz simultaneously, as part of the Monitoring Of GAmma-ray Bright AGN (MOGABA) program. We measured 3C~279 total flux densities of 22--34~Jy at 22~GHz, 15--28~Jy (43~GHz), and 10--21~Jy (86~GHz), showing mild variability of $\leq 50\,\%$ over the period of our observations. The spectral index between 22~GHz and 86~GHz ranged from $-0.13$ to $-0.36$. Linear polarization angles were 27$^{\circ}$--38$^{\circ}$, 30$^{\circ}$--42$^{\circ}$, and 33$^{\circ}$--50$^{\circ}$ at 22~GHz, 43~GHz, and 86~GHz, respectively. The degree of linear polarization was in the range of 6--12\,\%, and slightly decreased with time at all frequencies. We investigated Faraday rotation and depolarization of the polarized emission at 22--86~GHz, and found Faraday rotation measures (RM) of $-300$ to $-1200$~rad~m$^{-2}$ between 22~GHz and 43~GHz, and $-800$ to $-5100$~rad~m$^{-2}$ between 43~GHz and 86~GHz. The RM values follow a power law with a mean power law index $a$ of $2.2$, implying that the polarized emission at these frequencies travels through a Faraday screen in or near the jet. We conclude that the regions emitting polarized radio emission may be different from the region responsible for the 2013 December $\gamma$-ray flare and are maintained by the dominant magnetic field perpendicular to the direction of the radio jet at milliarcsecond scales.
We present neutral hydrogen (HI) and warm molecular hydrogen (H2) observations of the young (10^2 years) radio galaxy PKS B1718-649. We study the morphology and the kinematics of both gas components, focusing, in particular, on their properties in relation to the triggering of the radio activity. The regular kinematics of the large scale HI disk, seen in emission, suggests that an interaction event occurred too long ago to be responsible for the recent triggering of the radio activity. In absorption, we detect two absorption lines along the narrow line of sight of the compact (r<2 pc) radio source. The lines trace two clouds with opposite radial motions. These may represent a population of clouds in the very inner regions of the galaxy, which may be involved in triggering the radio activity. The warm molecular hydrogen (H2 1-0 S(1) ro-vibrational line) in the innermost kilo-parsec of the galaxy appears to be distributed in a circum-nuclear disk following the regular kinematics of the HI and of the stellar component. An exception to this behaviour arises only in the very centre, where a highly dispersed component is detected. These particular HI and H2 features suggest that a strong interplay between the radio source and the surrounding ISM is on-going. The physical properties of the cold gas in the proximity of the radio source may regulate the accretion recently triggered in this AGN.
The one-meter telescope-reflector `Saturn' (D=1 m, F = 4 m) was partially renovated at the Pulkovo observatory at the end of 2014. The telescope was equipped by CCD camera S2C with 14x14 arcmin field of view and 824 mas per pix scale. The observations of outer Jovian satellites have been performed in a test mode since January 2015. The exposure time of 30 seconds allows us to obtain images of stars up to magnitude 19.5 with the present state of the mirror and the equipment. The observations of outer Jovian satellites have been performed during testing period. These objects are interesting targets because their astrometric observations required to improve ephemeris and dynamic studies. Satellites positions have been determined on the basis of CCD images obtained within 6 nights. Astrometric reduction is performed by linear method using HCRF/UCAC4 and HCRF/URAT1. Internal accuracy of satellites positions has been estimated as 20 - 100 mas. The absolute values of residuals O-C do not exceed 100 mas in most cases. The independent tests have been carried out by the direct comparison with the results of observations of the Jovian satellite Himalia performed simultaneously by the Normal astrograph (the largest difference was 113 mas). This work has been partially supported by RFBR (12-02-00675-a) and the 22 Program of RAS Praesidium.
We present preliminary results of the quasar survey in Large Sky Area Multi- Object Fiber Spectroscopic Telescope (LAMOST) first data release (DR1), which includes pilot survey and the first year regular survey. There are 3921 quasars identified with reliability, among which 1180 are new quasars discovered in the survey. These quasars are at low to median redshifts, with highest z of 4.83. We compile emission line measurements around the H{\alpha}, H{\beta}, Mg II, and C IV regions for the new quasars. The continuum luminosities are inferred from SDSS photo- metric data with model fitting as the spectra in DR1 are non-flux-calibrated. We also compile the virial black hole mass estimates, and flags indicating the selec- tion methods, broad absorption line quasars. The catalog and spectra for these quasars are available online. 28% of the 3921 quasars are selected with optical- infrared colours independently, indicating that the method is quite promising in completeness of quasar survey. LAMOST DR1 and the on-going quasar survey will provide valuable data in the studies of quasars.
<Context.> Nuclear star clusters (NSCs) at the dynamical center of galaxies appear to have a complex star formation history. This suggests repeated star formation even in the influence of the strong tidal field from supermassive black holes. <Aim.> In our previous study, we have detected 31 so far unknown early-type star candidates throughout the Galactic NSC (at 0.5 - 3 pc from Sgr A*; Nishiyama and Schoedel 2013). The aim of this study is a confirmation of the spectral type for the candidates. <Method.> We have carried out NIR spectroscopic observations of the candidates using Subaru/IRCS/AO188/LGS. K-band spectra for 20 out of the 31 candidates were obtained. By determining an equivalent width, EW(CO), of the 12CO absorption feature at 2.294 um, we have derived an effective temperature and a bolometric magnitude for each candidate, and then constructed an HR diagram. <Results.> No young (~ Myr), massive stars are included in the 20 candidates we observed; however, 13 candidates are most likely intermediate-age giants (50 - 500 Myr). Two other sources have ages of ~1 Gyr, and the remaining five sources are old (> 1 Gyr), late-type giants. <Conclusions.> Although none of the early-type star candidates from our previous narrow-band imaging observations can be confirmed as a young star, we find that the photometric technique is sensitive to distinguish old, late-type giants from young and intermediate-age populations. The intermediate-age stars could be so far unknown members of a population formed in a starburst ~100 Myr ago. Finding no young (~ a few Myr) stars at R = 0.5 - 3 pc favors the in-situ formation scenario for the presence of the young stars at R < 0.5 pc. Furthermore, the different spatial distributions of the young and the intermediate-age stars imply that the Galactic NSC is an aggregate of stars born in different places and under different physical conditions.
With the Westerbork Synthesis Radio Telescope, we performed HI observations of a sample of known X-ray emitting Gigahertz-peaked-spectrum galaxies with compact-symmetric-object morphology (GPS/CSOs) that lacked an HI absorption detection. We combined radio and X-ray data of the full sample of X-ray emitting GPS/CSOs and found a significant, positive correlation between the column densities of the total and neutral hydrogen ($N_{\rm H}$ and $N_{\rm HI}$, respectively). Using a Bayesian approach, we simultaneously quantified the parameters of the $N_{\rm H} - N_{\rm HI}$ relation and the intrinsic spread of the data set. For a specific subset of our sample, we found $N_{\rm H} \propto N_{\rm HI}^b$, with $b=0.93^{+0.49}_{-0.33}$, and $\sigma_{int} (N_{\rm H})= 1.27^{+1.30}_{-0.40}$. The $N_{\rm H} - N_{\rm HI}$ correlation suggests a connection between the physical properties of the radio and X-ray absorbing gas.
We present the Cassini Atlas Of Stellar Spectra (CAOSS), comprised of near-infrared low-resolution spectra of bright stars recovered from space-based observations by the Cassini spacecraft. The 65 stellar targets in the atlas are predominately M, K and S giants. However it also contains spectra of other bright nearby stars including carbon stars and main sequence stars from A to F. The spectra presented are free of all spectral contamination caused by the Earth's atmosphere, including the detrimental telluric molecular bands which put parts of the near-infrared spectrum out of reach of terrestrial observations. With a single instrument, a spectro-photometric dataset is recovered that spans the near-infrared from 0.8 to 5.1 microns with spectral resolution ranging from R=53.5 to R=325. Spectra have been calibrated into absolute flux units after careful characterisation of the instrumental spectral efficiency. Spectral energy distributions for most stars match closely with literature values. All final data products have been made available online.
Context. The compositional properties of hydrogenated amorphous carbons are known to evolve in response to the local conditions. Aims. To present a model for low-temperature, amorphous hydrocarbon solids, based on the microphysical properties of random and defected networks of carbon and hydrogen atoms, that can be used to study and predict the evolution of their properties in the interstellar medium. Methods. We adopt an adaptable and prescriptive approach to model these materials, which is based on a random covalent network (RCN) model, extended here to a full compositional derivation (the eRCN model), and a defective graphite (DG) model for the hydrogen poorer materials where the eRCN model is no longer valid. Results. We provide simple expressions that enable the determination of the structural, infrared and spectral properties of amorphous hydrocarbon grains as a function of the hydrogen atomic fraction, XH. Structural annealing, resulting from hydrogen atom loss, results in a transition from H-rich, aliphatic-rich to H-poor, aromatic-rich materials. Conclusions. The model predicts changes in the optical properties of hydrogenated amorphous carbon dust in response to the likely UV photon-driven and/or thermal annealing processes resulting, principally, from the radiation field in the environment. We show how this dust component will evolve, compositionally and structurally in the interstellar medium in response to the local conditions.
Telescopes, designed with semi-conductor based photo sensors, have the potential to detect Cherenkov or fluorescence light emitted by cosmic-rays in the atmosphere. Such telescopes promise a high duty cycle and efficiency in remote harsh environments. Given the relatively low costs and robustness of these instruments, this technology could prove interesting especially if deployed in large numbers with existing and future extended cosmic-ray and gamma ray detectors, including the Pierre Auger observatory, HAWC, IceCube and CTA. They may have the potential to enhance the sensitivity of these instruments for the detection of high-energy gamma rays and cosmic-ray air showers. In addition, for neutrino telescopes such a technology could prove to be an efficient cosmic-ray veto on the surface. In this contribution the current motivation, design, and development of a prototype SiPM based air Cherenkov telescope is described. The results of initial sensitivity studies, and the readiness of the system for first tests, including those proposed for the South Pole are shown.
Context. The properties of hydrogenated amorphous carbon (a-C:H) dust are known to evolve in response to the local conditions. Aims. We present an adaptable model for the determination of the optical properties of low-temperature, interstellar a-C:H grains that is based on the fundamental physics of their composition. Methods. The imaginary part of the refractive index, k, for a-C:H materials, from 50 eV to cm wavelengths, is derived and the real part, n, of the refractive index is then calculated using the Kramers-Kronig relations. Results. The formulated optEC(s) model allows a determination of the complex dielectric function, epsilon, and refractive index, m(n, k), for a-C:H materials as a continuous function the band gap, Eg , which is shown to lie in the range = -0.1 to 2.7 eV. We provide expressions that enable a determination of their optical constants and tabulate m(n, k, Eg ) for 14 different values of Eg . We explore the evolution of the likely extinction and emission behaviours of a-C:H grains and estimate the relevant transformation time-scales. Conclusions. With the optEC(s) model we are able to predict how the optical properties of an a-C:H dust component in the interstellar medium will evolve in response to, principally, the local interstellar radiation field. The evolution of a-C:H materials appears to be consistent with many dust extinction, absorption, scattering and emission properties, and also with H2 molecule, daughter PAH and hydrocarbon molecule formation resulting from its photo-driven decomposition.
Recent observations opened up a new window on the inflationary model building. As it was firstly reported by the WMAP data, there may be some indications of statistical anisotropy on the CMB map, although the statistical significance of these findings are under debate. Motivated by these observations, people begun considering new inflationary models which may lead to statistical anisotropy. The simplest possible way to construct anisotropic inflation is to introduce vector fields. During the course of this thesis, we study models of anisotropic inflation and their observational implications such as power spectrum, bispectrum etc. Firstly we build a new model, which contains the gauge field which breaks the conformal invariance while preserving the gauge invariance. We show that in these kind of models, there can be an attractor phase in the evolution of the system when the back-reaction of the gauge field becomes important in the evolution of the inflaton field. We then study the cosmological perturbation theory in these kind of models. More specifically, we calculate the anisotropic corrections due to the presence of the vector field. We then generalize the separate universe formalism to our anisotropic set up and use it in some specific examples of anisotropic inflation. Finally, we connect the primordial anisotropies to the specific examples and to CMB observations. We calculate the TT, TE, TB, EB and BB correlation in the model of charged scalar field model and look for the unique signatures that the anisotropic inflation can have on the CMB map. Any future detection of these statistical anisotropies would rule out the isotropic FRW models.
Context. The properties of hydrogenated amorphous carbon (a-C:H) dust evolve in response to the local radiation field in the interstellar medium and the evolution of these properties is particularly dependent upon the particle size. Aims. A model for finite-sized, low-temperature amorphous hydrocarbon particles, based on the microphysical properties of random and defected networks of carbon and hydrogen atoms, with surfaces passivated by hydrogen atoms, has been developed. Methods. The eRCN/DG and the optEC(s) models have been combined, adapted and extended into a new optEC(s)(a) model that is used to calculate the optical properties of hydrocarbon grain materials down into the sub-nanometre size regime, where the particles contain only a few tens of carbon atoms. Results. The optEC(s)(a) model predicts a continuity in properties from large to small (sub-nm) carbonaceous grains. Tabulated data of the size-dependent optical constants (from EUV to cm wavelengths) for a-C:H (nano-)particles as a function of the bulk material band gap [Eg(bulk)], or equivalently the hydrogen content, are provided. The effective band gap [Eg(eff.)] is found to be significantly larger than Eg(bulk) for hydrogen-poor a-C(:H) nano-particles and their predicted long-wavelength ({\lambda} > 30{\mu}m) optical properties differ from those derived for interstellar polycyclic aromatic hydrocarbons (PAHs). Conclusions. The optEC(s)(a) model is used to investigate the size-dependent structural and spectral evolution of a-C(:H) materials under ISM conditions, including: the IR-FUV extinction, the 217 nm bump and the infrared emission bands. The model makes several predictions that can be tested against observations.
Generic scalar-tensor theories of gravity predict deviations from Newtonian physics inside astrophysical bodies. In this paper, we point out that low mass stellar objects, red and brown dwarf stars, are excellent probes of these theories. We calculate two important and potentially observable quantities: the radius of brown dwarfs and the minimum mass for hydrogen burning in red dwarfs. The brown dwarf radius can differ significantly from the GR prediction and upcoming surveys that probe the mass-radius relation for stars with masses $<\mathcal{O}(0.1M_\odot)$ have the potential to place new constraints. The minimum mass for hydrogen burning can be larger than several presently observed Red Dwarf stars. This places a new and extremely stringent constraint on the parameters that appear in the effective field theory of dark energy and rules out several well-studied dark energy models.
The binary system RW Aur consists of two classical T~Tauri stars (CTTSs). The primary recently underwent its second observed major dimming event ($\Delta V\,\sim2\,$mag). We present new, resolved Chandra X-ray and UKIRT near-IR (NIR) data as well as unresolved optical photometry obtained in the dim state to study the gas and dust content of the absorber causing the dimming. The X-ray data show that the absorbing column density increased from $N_H<0.1\times10^{22}\,$cm$^{-2}$ during the bright state to $\approx2\times10^{22}\,$cm$^{-2}$ in the dim state. The brightness ratio between dim and bright state at optical to NIR wavelengths shows only a moderate wavelength dependence and the NIR color-color diagram suggests no substantial reddening. Taken together, this indicates gray absorption by large grains ($\gtrsim1\,\mu$m) with a dust mass column density of $\gtrsim2\times10^{-4}\,$g$\,$cm$^{-2}$. Comparison with $N_H$ shows that an absorber responsible for the optical/NIR dimming and the X-ray absorption is compatible with the ISM's gas-to-dust ratio, i.e., that grains grow in the disk surface layers without largely altering the gas-to-dust ratio. Lastly, we discuss a scenario in which a common mechanism can explain the long-lasting dimming in RW Aur and recently in AA Tau.
Early-matter-like dark energy is defined as a dark energy component whose equation of state approaches that of cold dark matter (CDM) at early times. Such a component is an ingredient of unified dark matter (UDM) models, which unify the cold dark matter and the cosmological constant of the LambdaCDM concordance model into a single dark fluid. Power series expansions in conformal time of the perturbations of the various components for a model with early-matter-like dark energy are provided. They allow the calculation of the cosmic microwave background (CMB) anisotropy from the primordial initial values of the perturbations. For a phenomenological UDM model, which agrees with the observations of the local Universe, the CMB anisotropy is computed and compared with the CMB data. It is found that a match to the CMB observations is possible if the so-called effective velocity of sound c_eff of the early-matter-like dark energy component is very close to zero. The modifications on the CMB temperature and polarization power spectra caused by varying the effective velocity of sound are studied.
Massive stars having a CO core of $\sim 40 - 60$ M$_\odot$ experience pulsational pair-instability (PPI) after carbon-burning. This instability induces strong pulsations of the whole star and a part of outer envelope is ejected. We investigate the evolution and mass ejection of metal-poor very massive stars which experience PPI. We use stellar models with initial masses of 140, 200, and 250 M$_\odot$ and the metallicity Z=0.004. Their masses decrease to 54.09, 58.65, and 61.03 M$_\odot$ before the neon-burning owing to mass loss and He mass fraction at the surface becomes about 20%. During the PPI period of $\sim 1 - 2000$ years, they experience six, four, and three pulsations, respectively. The larger CO-core model has the longer PPI period and ejects the larger amount of mass. Since almost all surface He has been lost by the pulsations, these stars become type Ic supernovae if they explode. Light curves during the PPI stage and supernovae are investigated and are implicated in luminous supernovae. The luminosity created by the interaction of different PPI ejecta becomes $M_{\rm bol} \sim -16 - -20$. The interaction between the circumstellar shell ejected by PPI and the supernova ejecta can be more luminous. These luminous transients could be an origin of type I super-luminous supernovae and supernovae with precursor.
Arrival directions of 40 neutrino events with energies >~100 TeV, observed by the IceCube experiment, are studied. Their distribution in the Galactic latitude and in the angular distance to the Galactic Center allow to search for the Milky-Way disk and halo-related components, respectively. No statistically significant evidence for the disk component is found, though even 100% disk origin of the flux is allowed at the 90% confidence level. Contrary, the Galactic Center-Anticenter dipole anisotropy, specific for dark-matter decays (annihilation) or for interactions of cosmic rays with the extended halo of circumgalactic gas, is clearly favoured over the isotropic distribution (the probability of a fluctuation of the isotropic signal is ~2%).
We present optical imaging and spectroscopy of supernova (SN) LSQ13fn, a type II supernova with several hitherto-unseen properties. Although it initially showed strong symmetric spectral emission features attributable to \ion{He}{ii}, \ion{N}{iii}, and \ion{C}{iii}, reminiscent of some interacting SNe, it transitioned into an object that would fall more naturally under a type II-Plateau (IIP) classification. However, its spectral evolution revealed several unusual properties: metal lines appeared later than expected, were weak, and some species were conspicuous by their absence. Furthermore, the line velocities were found to be lower than expected given the plateau brightness, breaking the SNe~IIP standardised candle method for distance estimates. We found that, in combination with a short phase of early-time ejecta-circumstellar material interaction, metal-poor ejecta, and a large progenitor radius could reasonably account for the observed behaviour. Comparisons with synthetic model spectra of SNe~IIP of a given progenitor mass would imply a progenitor star metallicity as low as 0.1\,Z$_{\odot}$. LSQ13fn highlights the diversity of SNe~II and the many competing physical effects that come into play towards the final stages of massive star evolution immediately preceding core-collapse.
Transiting planets around stars are discovered mostly through photometric surveys. Unlike radial velocity surveys, photometric surveys do not tend to target slow rotators, inactive and metal-rich stars. Nevertheless, we suspect that observational biases could impact also transiting-planet hosts. This paper aims at evaluating how selection effects reflect on the evolutionary stage of both a limited sample of transiting-planet host stars (TPH) and a wider sample of planet-hosting stars detected through radial velocity analysis. Then, thanks to uniform derivation of stellar ages, a homogeneous comparison between exoplanet hosts and field star age distributions is developed. Stellar parameters have been computed through our custom-developed isochrone placement algorithm, according to Padova evolutionary models. The notable aspects of our algorithm include the treatment of element diffusion, activity checks in terms of $\log{R'_{HK}}$ and $v\sin{i}$ and the evaluation of the stellar evolutionary speed in the Hertzsprung-Russel Diagram in order to better constrain age. Working with TPH, the observational stellar mean density $\rho_{\star}$ allows to compute stellar luminosity even if the distance is not available, by combining $\rho_{\star}$ with the spectroscopic $\log{g}$. The median value of the TPH ages is $\sim5$ Gyr. Even if this sample is not so large, however the result is very similar to what we found for the sample of spectroscopic hosts, whose modal and median values are [3, 3.5) Gyr and $\sim4.8$ Gyr, respectively. Thus these stellar samples suffer almost the same selection effects. We also conclude that the age of our Sun is consistent with the age distribution of solar neighbourhood MS stars with spectral types from late-F to early-K, regardless of harbouring planets or not. We considered the possibility that our selected samples are older than the average disc population.
By considering all asteroid linear polarization data available in the literature, it is possible to obtain updated phase - polarization curves for several tens of objects. In a separate paper (Cellino et al., 2015a, MNRAS, 451, 3473) we have produced new calibrations of different relations between the geometric albedo and several polarimetric parameters, based on an analysis of a limited sample of asteroids for which the albedo is known with sufficient accuracy. In this paper, we present the main polarization parameters and corresponding albedos for a larger dataset of asteroids which we did not use for calibration purposes. We find a good agreement between the albedo values computed using different polarization parameters. Conversely, in the case of the so-called Barbarian asteroids the situation is rather unclear. Moreover, we present an updated analysis of the distributions of different polarimetric parameters, including the so-called inversion angle and the solar phase angle corresponding to the extreme value of negative polarization, and study their mutual relations. We find that the above parameters can be used to clearly distinguish some unusual classes of asteroids. Polarimetric parameters are known to be related to physical properties of asteroid surfaces which are difficult to infer by means of other observing techniques. By using a much larger dataset, in our analysis we confirm and extend some results obtained in the past by other authors, and we explore more systematically some features that had been mostly unexplored before, mainly concerning the morphology of the negative polarization branch.
We present first results from a LOFAR census of non-recycled pulsars. The census includes almost all such pulsars known (194 sources) at declinations Dec$> 8^\circ$ and Galactic latitudes |Gb|$> 3^\circ$, regardless of their expected flux densities and scattering times. Each pulsar was observed contiguously in the frequency range from 110$-$188 MHz and for $\geq 20$ minutes, recording full-Stokes data. We present the dispersion measures, flux densities, and calibrated total intensity profiles for the 158 pulsars detected in the sample. The median uncertainty in census dispersion measures ($1.5 \times 10^{-4}$ pc cm$^{-3}$) is ten times smaller, on average, than in the ATNF pulsar catalogue. We combined census flux densities with those in the literature and fitted the resulting broadband spectra with single or broken power-law functions. For 48 census pulsars such fits are being published for the first time. Typically, the choice between single and broken power-laws, as well as the location of the spectral break, were highly influenced by the spectral coverage of the available flux density measurements. In particular, the inclusion of measurements below 100 MHz appears essential for investigating the low-frequency turnover in the spectra for most of the census pulsars. For several pulsars, we compared the spectral indices from different works and found the typical spread of values to be within 0.5$-$1.5, suggesting a prevailing underestimation of spectral index errors in the literature. The census observations yielded some unexpected individual source results, as we describe in the paper. Lastly, we will provide this unique sample of wide-band, low-frequency pulse profiles via the European Pulsar Network Database.
Current models of gamma-ray lightcurves in pulsars suffer from large uncertainties on the precise location of particle acceleration and radiation. Here, we present an attempt to alleviate these difficulties by solving for the electromagnetic structure of the oblique magnetosphere, particle acceleration, and the emission of radiation self-consistently, using 3D spherical particle-in-cell simulations. We find that the low-energy radiation is synchro-curvature radiation from the polar-cap regions within the light cylinder. In contrast, the high-energy emission is synchrotron radiation that originates exclusively from the Y-point and the equatorial current sheet where relativistic magnetic reconnection accelerates particles. In most cases, synthetic high-energy lightcurves contain two peaks that form when the current sheet sweeps across the observer's line of sight. We find clear evidence of caustics in the emission pattern from the current sheet. High-obliquity solutions can present up to two additional secondary peaks from energetic particles in the wind region accelerated by the reconnection-induced flow near the current sheet. The high-energy radiative efficiency depends sensitively on the viewing angle, and decreases with increasing pulsar inclination. The high-energy emission is concentrated in the equatorial regions where most of the pulsar spindown is released and dissipated. These results have important implications for the interpretation of gamma-ray pulsar data.
We present the first model that couples high-resolution simulations of the
formation of Local Group galaxies with calculations of the galactic habitable
zone (GHZ), a region of space which has sufficient metallicity to form
terrestrial planets without being subject to hazardous radiation. These
simulations allow us to make substantial progress in mapping out the asymmetric
three-dimensional GHZ and its time evolution for the Milky Way (MW) and
Triangulum (M33) galaxies, as opposed to works that generally assume an
azimuthally symmetric GHZ.
Applying typical habitability metrics to MW and M33, we find that while a
large number of habitable planets exist as close as a few kiloparsecs from the
galactic centre, the probability of individual planetary systems being
habitable rises as one approaches the edge of the stellar disc. Tidal streams
and satellite galaxies also appear to be fertile grounds for habitable planet
formation.
In short, we find that both galaxies arrive at similar GHZs by different
evolutionary paths, as measured by the first and third quartiles of surviving
biospheres. For the Milky Way, this interquartile range begins as a narrow band
at large radii, expanding to encompass much of the galaxy at intermediate times
before settling at a range of 2-13kpc. In the case of M33, the opposite
behaviour occurs - the initial and final interquartile ranges are quite
similar, showing gradual evolution. This suggests that galaxy assembly history
strongly influences the time evolution of the GHZ, which will affect the
relative time lag between biospheres in different galactic locations. We end by
noting the caveats involved in such studies and demonstrate that high
resolution cosmological simulations will play a vital role in understanding
habitability on galactic scales, provided that these simulations accurately
resolve chemical evolution.
We report a new detection of neutral deuterium in the sub Damped Lyman Alpha system with low metallicity [O/H]\,=\,$-2.042 \pm 0.005$ at $z_{\rm abs}=2.437$ towards QSO~J\,1444$+$2919. The hydrogen column density in this system is log$N$(H\,{\sc i})~$=19.983\pm0.010$ and the measured value of deuterium abundance is log(D/H)~$=-4.706\pm0.007_{\rm stat}\pm0.067_{\rm syst}$. This system meets the set of strict selection criteria stated recently by Cooke et al. and, therefore, widens the {\it Precision Sample} of D/H. However, possible underestimation of systematic errors can bring bias into the mean D/H value (especially if use a weighted mean). Hence, it might be reasonable to relax these selection criteria and, thus, increase the number of acceptable absorption systems with measured D/H values. In addition, an unweighted mean value might be more appropriate to describe the primordial deuterium abundance. The unweighted mean value of the whole D/H data sample available to date (15 measurements) gives a conservative value of the primordial deuterium abundance (D/H)$_{\rm p}=(2.55\pm 0.19)\times10^{-5}$ which is in good agreement with the prediction of analysis of the cosmic microwave background radiation for the standard Big Bang nucleosynthesis. By means of the derived (D/H)$_{\rm p}$ value the baryon density of the Universe $\Omega_{\rm b}h^2=0.0222\pm0.0013$ and the baryon-to-photon ratio $\eta_{10} = 6.09\pm 0.36$ have been deduced. These values have confident intervals which are less stringent than that obtained for the {\it Precision Sample} and, thus, leave a broader window for new physics. The latter is particularly important in the light of the lithium problem.
With a deep Chandra/HETGS exposure of WR 6, we have resolved emission lines whose profiles show that the X-rays originate from a uniformly expanding spherical wind of high X-ray-continuum optical depth. The presence of strong helium-like forbidden lines places the source of X-ray emission at tens to hundreds of stellar radii from the photosphere. Variability was present in X-rays and simultaneous optical photometry, but neither were correlated with the known period of the system or with each other. An enhanced abundance of sodium revealed nuclear processed material, a quantity related to the evolutionary state of the star. The characterization of the extent and nature of the hot plasma in WR 6 will help to pave the way to a more fundamental theoretical understanding of the winds and evolution of massive stars.
In this paper we study the generation of very high energy (VHE) emission in Crab-like pulsars driven by means of the feedback of Cherenkov drift waves on distribution of magnetospheric electrons. We have found that the unstable Cherenkov drift modes lead to the quasi-linear diffusion (QLD), keeping the pitch angles from vanishing, which in turn, maintains the synchrotron mechanism. Considering the Crab-like pulsars it has been shown that the growth rate of the Cherenkov drift instability (ChDI) is quite high, indicating high efficiency of the process. Analyzing the mechanism for the typical parameters we have found that the Cherenkov drift emission from the extreme UV to hard $X$-rays is strongly correlated with the VHE synchrotron emission in the GeV band.
A better knowledge of Jovian satellites' origins will bring light on the environment that surrounded Jupiter during its formation and can help us to understand the characteristics of this unique satellite system. We developed a semi-analytical model to investigate Jupiter's regular satellite formation and present the results of our population synthesis calculations. We performed simulations adopting a massive, static, low-viscosity circumplanetary disk model, in agreement with a current study of magnetorotational instability in a circum-planetary disk. We find that the high gas density leads to very rapid migration of satellitesimals due to gas drag and type II migration of satellites in a faster disk-dominated mode. A large concentration of solids, large building blocks and longer type II migration time-scales favor formation and survival of large satellites. However, bodies as massive as Ganymede and those located far away from Jupiter, such as Callisto, are difficult to form with this scenario.
The coronagraph instrument on the WFIRST-AFTA mission study has two coronagraphic architectures, shaped pupil and hybrid Lyot, which may be interchanged for use in different observing scenarios. Each architecture relies on newly-developed mask components to function in the presence of the AFTA aperture, and so both must be matured to a high technology readiness level (TRL) in advance of the mission. A series of milestones were set to track the development of the technologies required for the instrument; in this paper, we report on completion of WFIRST-AFTA Coronagraph Milestone 2---a narrowband $10^{-8}$ contrast test with static aberrations for the shaped pupil---and the plans for the upcoming broadband Coronagraph Milestone 5.
We study the counter terms in the Eulerian version of the EFT of Large Scale Structure. We reformulate the equations to solve for the displacement of fluid elements as a bookkeeping variable and study the structure of the counter terms in this formulation. We show that in many cases the time dependence of the amplitude of the counter terms is irrelevant, as solutions obtained for various time dependences differ by terms that can be reabsorbed by higher order counter terms. We show that including all effects due to the non-locality in time and the time dependence of the counter terms there are six new parameters relevant for the two loop power spectrum calculation. We give explicit expressions for all these terms and study the contributions to them from large and small modes. We show that the shape of all these terms is very similar.
The center-of-mass energy of two particles can become arbitrarily large if they collide near the event horizon of an extremal Kerr black hole, which is called the Ba$\rm \tilde n$ados-Silk-West (BSW) effect. We consider such a high-energy collision of two particles which started from infinity and follow geodesics in the equatorial plane and investigate the energy extraction from such a high-energy particle collision and the production of particles in the equatorial plane. We analytically show that, on the one hand, if the produced particles are as massive as the colliding particles, the energy-extraction efficiency is bounded by $2.19$ approximately. On the other hand, if a very massive particle is to be produced as a result of the high-energy collision, which has negative energy and necessarily falls into the black hole, the upper limit of the energy-extraction efficiency is increased to $(2+\sqrt{3})^2 \simeq 13.9$. Thus, higher efficiency of the energy extraction, which is typically as large as 10, provides strong evidence for the production of a heavy particle.
We investigate matter couplings in massive bigravity. We find a new family of such consistent couplings, including and extending known consistent matter couplings, and we investigate their decoupling limits, ADM decompositions, Higuchi bounds and further aspects. We show that differences to previous known consistent couplings only arise beyond the $\Lambda_3$ decoupling limit and discuss the uniqueness of consistent matter couplings and how this is related to the so-called symmetric vielbein condition. Since we work in a vielbein formulation, these results easily generalise to multi-gravity.
The Einstein Telescope is a conceived third generation gravitational-wave detector that is envisioned to be an order of magnitude more sensitive than advanced LIGO, Virgo and Kagra, which would be able to detect gravitational-wave signals from the coalescence of compact objects with waveforms starting as low as 1Hz. With this level of sensitivity, we expect to detect sources at cosmological distances. In this paper we introduce an improved method for the generation of mock data and analyse it with a new low latency compact binary search pipeline called gstlal. We present the results from this analysis with a focus on low frequency analysis of binary neutron stars. Despite compact binary coalescence signals lasting hours in the Einstein Telescope sensitivity band when starting at 5 Hz, we show that we are able to discern various overlapping signals from one another. We also determine the detection efficiency for each of the analysis runs conducted and and show a proof of concept method for estimating the number signals as a function of redshift. Finally, we show that our ability to recover the signal parameters has improved by an order of magnitude when compared to the results of the first mock data and science challenge. For binary neutron stars we are able to recover the total mass and chirp mass to within 0.5% and 0.05%, respectively.
A detailed understanding of a volcano inner structure is one of the key-points for the volcanic hazards evaluation. To this aim, in the last decade, geophysical radiography techniques using cosmic muon particles have been proposed. By measuring the differential attenuation of the muon flux as a function of the amount of rock crossed along different directions, it is possible to determine the density distribution of the interior of a volcano. Up to now, a number of experiments have been based on the detection of the muon tracks crossing hodoscopes, made up of scintillators or nuclear emulsion planes. Using telescopes based on the atmospheric Cherenkov imaging technique, we propose a new approach to study the interior of volcanoes detecting the Cherenkov light produced by relativistic cosmic-ray muons that survive after crossing the volcano. The Cherenkov light produced along the muon path is imaged as a typical annular pattern containing all the essential information to reconstruct particle direction and energy. Our new approach offers the advantage of a negligible background and an improved spatial resolution. To test the feasibility of our new method, we have carried out simulations with a toy-model based on the geometrical parameters of ASTRI SST-2M, i.e. the imaging atmospheric Cherenkov telescope currently under installation onto the Etna volcano. Comparing the results of our simulations with previous experiments based on particle detectors, we gain at least a factor of 10 in sensitivity. The result of this study shows that we resolve an empty cylinder with a radius of about 100 m located inside a volcano in less than 4 days, which implies a limit on the magma velocity of 5 m/h.
Unimodular Gravity (UG) is a restricted version of General Relativity (GR) in which the determinant of the metric is a fixed function and the field equations are given by the trace-free part of the full Einstein equations. The background equations in UG and GR are identical. It was recently claimed that, the first order contribution in the temperature fluctuation of the Cosmic Microwave Background (CMB) in UG is different from GR. In this work, we calculate the first order perturbation equations in UG and show that the Sachs-Wolfe effect in UG, in terms of gauge invariant variables, is identical to GR. We also show that the second order perturbation equation of Mukhnanov-Sasaki variable in UG, is identical to GR. The only difference comes from the gauge choices due the constraint on the metric determinant. Hence, UG and GR are identical and indistinguishable in CMB data on large scales.
Many alternatives to canonical slow-roll inflation have been proposed over the years, one of the main motivations being to have a model, capable of generating observable values of non-Gaussianity. In this work, we (re-)explore the physical implications of a great majority of such models within a single, effective field theory framework (including novel models with large non-Gaussianity discussed for the first time below.) The constraints we apply---both theoretical and experimental---are found to be rather robust, determined to a great extent by just three parameters: the coefficients of the quadratic EFT operators $(\delta N)^2$ and $\delta N \delta E$, and the slow-roll parameter $\varepsilon$. This allows to significantly limit the majority of single-field alternatives to canonical slow-roll inflation. While the existing data still leaves some room for most of the considered models, the situation would change dramatically if the current upper limit on the tensor-to-scalar ratio decreased down to $r < 10^{-2}$. Apart from inflationary models driven by plateau-like potentials, the single-field model that would have a chance of surviving this bound is the recently proposed slow-roll inflation with weakly-broken galileon symmetry. In contrast to \textit{canonical} slow-roll inflation, the latter model can support $r < 10^{-2}$ even if driven by a convex potential, as well as generate observable values for the amplitude of non-Gaussianity.
Cassini states correspond to equilibria of the spin axis of a celestial body when its orbit is perturbed. They were initially described for planetary satellites, but the spin axes of black-hole binaries also present this kind of equilibria. In previous works, Cassini states were reported as spin-orbit resonances, but actually the spin of black-hole binaries is in circulation and there is no resonant motion. Here we provide a general description of the spin dynamics of black-hole binary systems based on a Hamiltonian formalism. In absence of dissipation the problem is integrable and it is easy to identify all possible trajectories for the spin for a given value of the total angular momentum. As the system collapses due to radiation reaction, the Cassini states are shifted to different positions, which modifies the dynamics around them. This is why the final spin distribution may differ from the initial one. Our method provides a simple way of predicting the distribution of the spin of black-hole binaries at the end of the inspiral phase.
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