We report the detection of seven low mass companions to intermediate-mass stars (SpT B/A/F; $M$$\approx$1.5-4.5 solar masses) in the Scorpius-Centaurus Association using nonredundant aperture masking interferometry. Our newly detected objects have contrasts $\Delta L'$$\approx$4-6, corresponding to masses as low as $\sim$20 Jupiter masses and mass ratios of $q$$\approx$0.01-0.08, depending on the assumed age of the target stars. With projected separations $\rho$$\approx$10-30 AU, our aperture masking detections sample an orbital region previously unprobed by conventional adaptive optics imaging of intermediate mass Scorpius-Centaurus stars covering much larger orbital radii ($\approx$30-3000 AU). At such orbital separations, these objects resemble higher mass versions of the directly imaged planetary mass companions to the 10-30 Myr, intermediate-mass stars HR 8799, $\beta$ Pictoris, and HD95086. These newly discovered companions span the brown dwarf desert, and their masses and orbital radii provide a new constraint on models of the formation of low-mass stellar and substellar companions to intermediate-mass stars.
We study 203 extended X-ray sources in the Swift GRB fields that are located within the Sloan Digital Sky Survey (SDSS) DR8 footprint. We search for galaxy over-densities in three-dimensional space using SDSS galaxies and their photometric redshifts near the Swift cluster candidates. We find 103 Swift clusters with a >3 sigma over-density. The remaining targets are potentially located at higher redshifts and require deeper optical follow-up observations for confirmations as galaxy clusters. We present a series of cluster properties including the redshift, BCG magnitude, BCG-to-X-ray center offset, optical richness, and X-ray luminosity. We also detect red sequences in almost half of the 103 confirmed clusters. The X-ray luminosity and optical richness for the SDSS confirmed Swift clusters are correlated and follow previously established relations. The distribution of the separations between the X-ray centroids and the most likely BCG is also consistent with expectation. We compare the observed redshift distribution of the sample with a theoretical model, and find that our sample is complete for z < 0.3 and is still 80% complete up to z < 0.4, consistent with the survey depth of SDSS. These analysis results suggest that our Swift cluster selection algorithm has yielded a statistically well-defined cluster sample for further studying cluster evolution and cosmology. We also match our SDSS confirmed Swift clusters to existing cluster catalogs, and find 42, 2 and 1 matches in optical, X-ray and SZ catalogs, respectively, so the majority of these clusters are new detections.
We investigate the motion of the primary beam outside the light cylinder in the pulsar wind. Inside the light cylinder both primary and secondary plasma move along dipole magnetic field lines where their energies can be arbitrary. But at larger distances the theory predicts quasi-radial motion with the velocity exactly corresponding to the drift velocity which cannot be the same for primary and secondary plasma. Hence, the deceleration of the primary beam is to take place simultaneously resulting in the acceleration of the secondary plasma. We investigate this process in the three-fluid MHD approximation and demonstrate that for most pulsars the energy of the beam remains practically unchanged. Only for young radio pulsars (Crab, Vela) essential deceleration up to the energy of the secondary plasma takes place outside the fast magnetosonic surface $r_{\rm F} \sim (10$-$100) R_{\rm L}$, the energy of secondary plasma itself increasing insufficiently.
We present the first cosmological measurement derived from a galaxy density
field subject to a `clipping' transformation. By enforcing an upper bound on
the galaxy number density field in the Galaxy and Mass Assembly survey (GAMA),
contributions from the nonlinear processes of virialisation and galaxy bias are
greatly reduced. This leads to a galaxy power spectrum which is easier to
model, without calibration from numerical simulations.
We develop a theoretical model for the power spectrum of a clipped field in
redshift space, which is exact for the case of anisotropic Gaussian fields.
Clipping is found to extend the applicability of the conventional Kaiser
prescription by more than a factor of three in wavenumber, or a factor of
thirty in terms of the number of Fourier modes. By modelling the galaxy power
spectrum on scales k < 0.3 h/Mpc and density fluctuations $\delta_g < 4$ we
measure the normalised growth rate $f\sigma_8(z = 0.18) = 0.29 \pm 0.10$.
We measure the intrinsic Faber-Jackson (F-J) relation between velocity dispersion $\sigma$ and luminosity $L$ for massive, luminous red galaxies (LRGs) at redshift z~0.55. We achieve unprecedented precision by using a sample of 600,000 galaxies with spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) of the third Sloan Digital Sky Survey (SDSS-III). We deconvolve the effects of photometric errors, limited spectroscopic signal-to-noise ratio, and red--blue galaxy confusion using a novel hierarchical Bayesian formalism that is generally applicable to any combination of photometric and spectroscopic observables. For a F-J relation of the form $L \propto \sigma^{\beta}$, we find $\beta = 7.8 \pm 1.1$ for $\sigma$ corrected to the effective radius. We find a very small intrinsic scatter of $s = 0.047 \pm 0.004$ in $\log_{10} \sigma$ at fixed $L$. Assuming plausible stellar population models, our measurements are consistent with no evolution in the parameters of the F-J relation over the range 0.5 < z < 0.7 covered by the sample. The steep F-J slope indicates that the scaling relations for the most massive LRGs are systematically different than the relations defined at lower masses, and the small scatter suggests that these galaxies more closely approximate a one-parameter family than their less massive counterparts. The curvature of the F-J relation has been observed previously in lower-mass and/or smaller galaxy samples; this new work provides a definitive measurement of the high-mass limit of the relation. Our results reinforce a picture in which the formation of LRGs is primarily driven by major dissipationless mergers.
We present the analysis of the radio jet evolution of the radio galaxy 3C 120 during a period of prolonged gamma-ray activity detected by the Fermi satellite between December 2012 and October 2014. We find a clear connection between the gamma-ray and radio emission, such that every period of gamma-ray activity is accompanied by the flaring of the mm-VLBI core and subsequent ejection of a new superluminal component. However, not all ejections of components are associated with gamma-ray events detectable by Fermi. Clear gamma-ray detections are obtained only when components are moving in a direction closer to our line of sight.This suggests that the observed gamma-ray emission depends not only on the interaction of moving components with the mm-VLBI core, but also on their orientation with respect to the observer. Timing of the gamma-ray detections and ejection of superluminal components locate the gamma-ray production to within almost 0.13 pc from the mm-VLBI core, which was previously estimated to lie about 0.24 pc from the central black hole. This corresponds to about twice the estimated extension of the broad line region, limiting the external photon field and therefore suggesting synchrotron self Compton as the most probable mechanism for the production of the gamma-ray emission. Alternatively, the interaction of components with the jet sheath can provide the necessary photon field to produced the observed gamma-rays by Compton scattering.
We have observed two kinematically offset active galactic nuclei (AGN), whose ionised gas is at a different line-of-sight velocity to their host galaxies, with the SAMI integral field spectrograph (IFS). One of the galaxies shows gas kinematics very different to the stellar kinematics, indicating a recent merger or accretion event. We demonstrate that the star formation associated with this event was triggered within the last 100 Myr. The other galaxy shows simple disc rotation in both gas and stellar kinematics, aligned with each other, but in the central region has signatures of an outflow driven by the AGN. Other than the outflow, neither galaxy shows any discontinuity in the ionised gas kinematics at the galaxy's centre. We conclude that in these two cases there is no direct evidence of the AGN being in a supermassive black hole binary system. Our study demonstrates that selecting kinematically offset AGN from single-fibre spectroscopy provides, by definition, samples of kinematically peculiar objects, but IFS or other data are required to determine their true nature.
Galaxy proto-clusters at z >~ 2 provide a direct probe of the rapid mass assembly and galaxy growth of present day massive clusters. Because of the need of precise galaxy redshifts for density mapping and the prevalence of star formation before quenching, nearly all the proto-clusters known to date were confirmed by spectroscopy of galaxies with strong emission lines. Therefore, large emission-line galaxy surveys provide an efficient way to identify proto-clusters directly. Here we report the discovery of a large-scale structure at z = 2.44 in the HETDEX Pilot Survey. On a scale of a few tens of Mpc comoving, this structure shows a complex overdensity of Lya emitters (LAE), which coincides with broad-band selected galaxies in the COSMOS/UltraVISTA photometric and zCOSMOS spectroscopic catalogs, as well as overdensities of intergalactic gas revealed in the Lya absorption maps of Lee et al. (2014). We construct mock LAE catalogs to predict the cosmic evolution of this structure. We find that such an overdensity should have already broken away from the Hubble flow, and part of the structure will collapse to form a galaxy cluster with 10^14.5 +- 0.4 M_sun by z = 0. The structure contains a higher median stellar mass of broad-band selected galaxies, a boost of extended Lya nebulae, and a marginal excess of active galactic nuclei relative to the field, supporting a scenario of accelerated galaxy evolution in cluster progenitors. Based on the correlation between galaxy overdensity and the z = 0 descendant halo mass calibrated in the simulation, we predict that several hundred 1.9 < z < 3.5 proto-clusters with z = 0 mass of > 10^14.5 M_sun will be discovered in the 8.5 Gpc^3 of space surveyed by the Hobby Eberly Telescope Dark Energy Experiment.
Molecular oxygen, O_2, has been the target of ground-based and space-borne searches for decades. Of the thousands of lines of sight surveyed, only those toward Rho Oph and Orion H_2 Peak 1 have yielded detections of any statistical significance. The detection of the O_2 N_J =3_3 -1_2 and 5_4 - 3_4 lines at 487.249 GHz and 773.840 GHz, respectively, toward Rho Ophiuchus has been attributed to a short-lived peak in the time-dependent, cold-cloud O_2 abundance, while the detection of the O_2 N_J =3_3 - 1_2, 5_4 - 3_4 lines, plus the 7_6 - 5_6 line at 1120.715 GHz, toward Orion has been ascribed to time-dependent preshock physical and chemical evolution and low-velocity (12 km/s) non-dissociative C-type shocks, both of which are fully shielded from far-ultraviolet (FUV) radiation, plus a postshock region that is exposed to a FUV field. We report a re-interpretation of the Orion O_2 detection based on new C-type shock models that fully incorporate the significant effects the presence of even a weak FUV field can have on the preshock gas, shock structure and postshock chemistry. In particular, we show that a family of solutions exists, depending on the FUV intensity, that reproduces both the observed O_2 intensities and O_2 line ratios. The solution in closest agreement with the shock parameters inferred for H_2 Peak 1 from other gas tracers assumes a 23 km/s shock impacting gas with a preshock density of 8x10^4 cm^-3 and G_0 =1, substantially different from that inferred for the fully-shielded shock case. As pointed out previously, the similarity between the LSR velocity of all three O_2 lines (~11 km/s) and recently measured H_2O 5_32 - 4_41 maser emission at 620.701 GHz toward H_2 Peak 1 suggests that the O_2 emission arises behind the same shocks responsible for the maser emission, though the O_2 emission is almost certainly more extended than the localized high density maser spots
Spectropolarimetric measurements at moderate spectral resolutions are effective tracers of stellar magnetic fields and circumstellar environments when signal to noise ratios (SNRs) above 2000 can be achieved. The LRISp spectropolarimeter is capable of achieving these SNRs on faint targets with the 10m aperture of the Keck telescope, provided several instrumental artifacts can be suppressed. We describe here several methods to overcome instrumental error sources that are required to achieve these high SNRs on LRISp. We explore high SNR techniques such as defocusing and slit-stepping during integration with high spectral and spatial oversampling. We find that the instrument flexure and interference fringes introduced by the achromatic retarders create artificial signals at 0.5\% levels in the red channel which mimic real stellar signals and limit the sensitivity and calibration stability of LRISp. Careful spectral extraction and data filtering algorithms can remove these error sources. For faint targets and long exposures, cosmic ray hits are frequent and present a major limitation to the upgraded deep depletion red-channel CCD. These must be corrected to the same high SNR levels, requiring careful spectral extraction using iterative filtering algorithms. We demonstrate here characterization of these sources of instrumental polarization artifacts and present several methods used to successfully overcome these limitations. We have measured the linear to circular cross-talk and find it to be roughly 5\%, consistent with the known instrument limitations. We show spectropolarimetric signals on brown dwarfs are clearly detectable at 0.2\% amplitudes with sensitivities better than 0.05\% at full spectral sampling in atomic and molecular bands. Future LRISp users can perform high sensitivity observations with high quality calibration when following the described algorithms.
The two main advantages of space-based observation of extreme energy ($\gtrsim5\times10^{19}$ eV) cosmic rays (EECRs) over ground based observatories are the increased field of view and the full-sky coverage with nearly uniform systematics across the entire sky. The former guarantees increased statistics, whereas the latter enables a clean partitioning of the sky into spherical harmonics. The discovery of anisotropies would help to identify the long sought origin of EECRs. We begin an investigation of the reach of a full-sky space-based experiment such as EUSO to detect anisotropies in the extreme-energy cosmic-ray sky compared to ground based partial-sky experiments such as the Pierre Auger Observatory and Telescope Array. The technique is explained here, and simulations for a Universe with just two nonzero multipoles, monopole plus either dipole or quadrupole, are presented. These simulations quantify the advantages of space-based, all-sky coverage.
Supernovae type Ia (SNIa) are used as "standard candles" for cosmological
distance scales. To fit their light curve shape -- absolute luminosity
relation, one needs to assume an intrinsic color and a likelihood of host
galaxy extinction or a convolution of these, a color distribution prior. The
host galaxy extinction prior is typically assumed to be an exponential drop-off
for the current supernova programs ($P(A_V) \propto e^{-A_V/\tau_0}$). We
explore the validity of this prior using the distribution of extinction values
inferred when two galaxies accidentally overlap (an occulting galaxy pair). We
correct the supernova luminosity distances from the SDSS-III Supernova projects
(SDSS-SN) by matching the host galaxies to one of three templates from
occulting galaxy pairs based on the host galaxy mass and the $A_V$-bias -
prior-scale ($\tau_0$) relation from Jha et al. (2007).
We find that introducing an $A_V$ prior that depends on host mass results in
lowered luminosity distances for the SDSS-SN on average but it does not reduce
the scatter in individual measurements. This points, in our view, to the need
for many more occulting galaxy templates to match to SNIa host galaxies to rule
out this possible source of scatter in the SNIa distance measurements. We match
occulting galaxy templates based on both mass and projected radius and we find
that one should match by stellar mass first with radius as a secondary
consideration. We discuss the caveats of the current approach and our aim is to
convince the reader that a library of occulting galaxy pairs observed with HST
will provide sufficient priors to improve (optical) SNIa measurements to the
next required accuracy in Cosmology.
A promising formation channel of SMBHs at redshift 6 is the so-called DC model, which posits that a massive seed BH forms through gravitational collapse of a $\sim 10^5~M_\odot$ SMS. We study the evolution of such a SMS growing by rapid mass accretion. In particular, we examine the impact of time-dependent mass accretion of repeating burst and quiescent phases that are expected to occur with a self-gravitating circumstellar disk. We show that the stellar evolution with such episodic accretion differs qualitatively from that expected with a constant accretion rate, even if the mean accretion rate is the same. Unlike the case of constant mass accretion, whereby the star expands roughly following $R_* \simeq 2.6 \times 10^3 R_\odot (M_*/100~M_\odot)^{1/2}$, the protostar can substantially contract during the quiescent phases between accretion bursts. The stellar effective temperature and ionizing photon emissivity increase accordingly as the star contracts, which can cause strong ionizing feedback and halt the mass accretion onto the star. With a fixed duration of the quiescent phase $\Delta t_{\rm q}$, such contraction occurs in early evolutionary phases, i.e. for $M_* \lesssim 10^3~M_\odot$ with $\Delta t_{\rm q} \simeq 10^3$ yr. For later epochs and larger masses but the same $\Delta t_{\rm q}$, contraction is negligible even during quiescent phases. With larger quiescent times $\Delta t_{\rm q}$, however, the star continues to contract during quiescent phases even for the higher stellar masses. We show that such behavior is well understood by comparing the interval time and the thermal relaxation time for a bloated surface layer. We conclude that the UV radiative feedback becomes effective if the quiescent phase associated by the burst accretion is longer than $\sim 10^3$ yr, which is possible in an accretion disk forming in the direct collapse model.
In this paper, we study several issues in the linear equation-of-motion (EoM) and in-in approaches of computing the two-point correlation functions in multi-field inflation. We prove the equivalence between this EoM approach and the first-principle in-in formalism. We check this equivalence using several explicit examples, including cases with scale-invariant corrections and scale-dependent features. Motivated by the explicit proof, we show that the usual procedures in these approaches can be extended and applied to some interesting model categories beyond what has been studied in the literature so far. These include the density perturbations with strong couplings and correlated multi-field initial states.
The escape dynamics in a simple analytical gravitational model which describes the motion of stars in a Seyfert galaxy is investigated in detail. We conduct a thorough numerical analysis distinguishing between regular and chaotic orbits as well as between trapped and escaping orbits, considering only unbounded motion for several energy levels. In order to distinguish safely and with certainty between ordered and chaotic motion, we apply the Smaller ALingment Index (SALI) method. It is of particular interest to locate the escape basins through the openings around the collinear Lagrangian points $L_1$ and $L_2$ and relate them with the corresponding spatial distribution of the escape times of the orbits. Our exploration takes place both in the physical $(x,y)$ and in the phase $(x,\dot{x})$ space in order to elucidate the escape process as well as the overall orbital properties of the galactic system. Our numerical analysis reveals the strong dependence of the properties of the considered escape basins with the total orbital energy, with a remarkable presence of fractal basin boundaries along all the escape regimes. It was also observed, that for energy levels close to the critical escape energy the escape rates of orbits are large, while for much higher values of energy most of the orbits have low escape periods or they escape immediately to infinity. We also present evidence obtained through numerical simulations that our model can describe the formation and the evolution of the observed spiral structure in Seyfert galaxies. We hope our outcomes to be useful for a further understanding of the escape mechanism in galaxies with active nuclei.
The 11.3 $\mu$m emission feature is a prominent member of the family of unidentified infrared emission (UIE) bands and is frequently attributed to out-of-plane bending modes of polycyclic aromatic hydrocarbon (PAH) molecules. We have performed quantum mechanical calculations of 60 neutral PAH molecules and found that it is difficult to reconcile the observed astronomical feature with any or a mix of these PAH molecules. We have further analyzed the fitting of spectra of several astronomical objects by the NASA PAH database program and found that reasonable fittings to the observed spectra are only possible by including significant contributions from oxygen and/or magnesium containing molecules in the mix. A mixed of pure PAH molecules, even including units of different sizes, geometry and charged states, is unable to fit the astronomical spectra. Preliminary theoretical results on the vibrational spectra of simple molecules with mixed aromatic/aliphatic structures show that these structures have consistent bundles of vibrational modes and could be viable carriers of the UIE bands.
Stationary orbits of dust particles after averaging over a synodic period in mean motion resonances in the circular restricted three-body problem with radiation are investigated. Conditions for the stationary orbits are obtained from averaged resonant equations. The stellar radiation with assumed rotational symmetry significantly simplifies the obtained system of equations for stationary points. In this case dust particles with all dimensions leading to bound orbits in exact resonances can be considered at once. Stationary points exist only at orbits with specific values of eccentricity (universal eccentricities). It is analytically shown that for variability of the longitude of pericenter in the stationary point (the particle's semimajor axis and libration center are stationary) another specific values of the eccentricity are required. These are, in general, different from the universal eccentricities and consequently the longitude of pericenter in the stationary point must also be stationary. An evolution in the exact resonance is periodic only if the longitude of pericenter is stationary. Numerical solution of the obtained system for the stationary orbits shows that for nine major exact mean motion resonances does not exist any stationary solution for the electromagnetic radiation and the radial stellar wind.
In this lecture I discuss the bulk surface heterogeneity of rotating stars, namely gravity darkening. I especially detail the derivation of the omega-model of Espinosa Lara & Rieutord (2011), which gives the gravity darkening in early-type stars. I also discuss the problem of deriving gravity darkening in stars owning a convective envelope and in those that are members of a binary system.
We use an updated version of SimProp, a Monte Carlo simulation scheme for the propagation of ultra-high energy cosmic rays, to compute cosmogenic neutrino fluxes expected on Earth in various scenarios. These fluxes are compared with the newly detected IceCube events at PeV energies and with recent experimental limits at EeV energies of the Pierre Auger Observatory. This comparison allows us to draw some interesting conclusions about the source models for ultra-high energy cosmic rays. We will show how the available experimental observations are almost at the level of constraining such models, mainly in terms of the injected chemical composition and cosmological evolution of sources. The results presented here will also be important in the evaluation of the discovery capabilities of the future planned ultra-high energy cosmic ray and neutrino observatories.
Here we introduce moments of visibility function and discuss how those can be used to estimate the power spectrum of the turbulent velocity of external spiral galaxies. We perform numerical simulation to confirm the credibility of this method and found that for galaxies with lower inclination angles it works fine. This is the only method to estimate the power spectrum of the turbulent velocity fluctuation in the ISM of the external galaxies.
4U 1630-472 is a recurrent X-ray transient classified as a black-hole candidate from its spectral and timing properties. One of the peculiarities of this source is the presence of regular outbursts with a recurrence period between 600 and 730 d that has been observed since the discovery of the source in 1969. We report on a comparative study on the spectral and timing behaviour of three consecutive outbursts occurred in 2006, 2008 and 2010. We analysed all the data collected by the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) and the Rossi X-ray timing Explorer (RXTE) during these three years of activity. We show that, in spite of having a similar spectral and timing behaviour in the energy range between 3 and 30 keV, these three outbursts show pronounced differences above 30 keV. In fact, the 2010 outburst extends at high energies without any detectable cut-off until 150-200 keV, while the two previous outbursts that occurred in 2006 and 2008 are not detected at all above 30 keV. Thus, in spite of a very similar accretion disk evolution, these three outbursts exhibit totally different characteristics of the Compton electron corona, showing a softening in their evolution rarely observed before in a low mass X-ray binary hosting a black hole. We argue the possibility that the unknown perturbation that causes the outbursts to be equally spaced in time could be at the origin of this particular behaviour. Finally we describe several possible scenarios that could explain the regularity of the outbursts, identifying the most plausible, such as a third body orbiting around the binary system.
Context. The inner disc, linking the thin disc with the bulge, has been somehow neglected in the past because of intrinsic difficulties in its study, due, e.g., to crowding and high extinction. Open clusters located in the inner disc are among the best tracers of its chemistry at different ages and distances. Aims. We analyse the chemical patterns of four open clusters located within 7 kpc of the Galactic Centre and of field stars to infer the properties of the inner disc with the Gaia-ESO survey idr2/3 data release. Methods. We derive the parameters of the newly observed cluster, Berkeley 81, finding an age of about 1 Gyr and a Galactocentric distance of 5.4 kpc. We construct the chemical patterns of clusters and we compare them with those of field stars in the Solar neighbourhood and in the inner-disc samples. Results. Comparing the three populations we observe that inner-disc clusters and field stars are both, on average, enhanced in [O/Fe], [Mg/Fe] and [Si/Fe]. Using the idr2/3 results of M67, we estimate the non-local thermodynamic equilibrium (NLTE) effect on the abundances of Mg and Si in giant stars. After empirically correcting for NLTE effects, we note that NGC 6705 and Be 81 still have a high [{\alpha}/Fe]. Conclusions. The location of the four open clusters and of the field population reveals that the evolution of the metallicity [Fe/H] and of [alpha/Fe] can be explained within the framework of a simple chemical evolution model: both [Fe/H] and [{\alpha}/Fe] of Trumpler 20 and of NGC 4815 are in agreement with expectations from a simple chemical evolution model. On the other hand, NGC 6705, and at a lower level Berkeley 81, have higher [{\alpha}/Fe] than expected for their ages, location in the disc, and metallicity. These differences might originate from local enrichment processes as explained in the inhomogeneous evolution framework.
We present new VLT/X-Shooter optical and NIR spectra of a sample of 17 candidate young low-mass stars and BDs in the rho-Ophiucus cluster. We derived SpT and Av for all the targets, and then we determined their physical parameters. All the objects but one have M*<0.6 Msun, and 8 have mass below or close to the hydrogen-burning limit. Using the intensity of various emission lines present in their spectra, we determined the Lacc and Macc for all the objects. When compared with previous works targeting the same sample, we find that, in general, these objects are not as strongly accreting as previously reported, and we suggest that the reason is our more accurate estimate of the photospheric parameters. We also compare our findings with recent works in other slightly older star-forming regions to investigate possible differences in the accretion properties, but we find that the accretion properties for our targets have the same dependence on the stellar and substellar parameters as in the other regions. This leads us to conclude that we do not find evidence for a different dependence of Macc with M* when comparing low-mass stars and BDs. Moreover, we find a similar small (1 dex) scatter in the Macc-M* relation as in some of our recent works in other star-forming regions, and no significant differences in Macc due to different ages or properties of the regions. The latter result suffers, however, from low statistics and sample selection biases in the current studies. The small scatter in the Macc-M* correlation confirms that Macc in the literature based on uncertain photospheric parameters and single accretion indicators, such as the Ha width, can lead to a scatter that is unphysically large. Our studies show that only broadband spectroscopic surveys coupled with a detailed analysis of the photospheric and accretion properties allows us to properly study the evolution of disk accretion rates.
Measurements of oscillation frequencies of the Sun and stars can provide important independent constraints on their internal structure and dynamics. Seismic models of these oscillations are used to connect structure and rotation of the star to its resonant frequencies, which are then compared with observations, the goal being that of minimizing the difference between the two. Even in the case of the Sun, for which structure models are highly tuned, observed frequencies show systematic deviations from modeled frequencies, a phenomenon referred to as the "surface term." The dominant source of this systematic effect is thought to be vigorous near-surface convection, which is not well accounted for in both stellar modeling and mode-oscillation physics. Here we bring to bear the method of homogenization, applicable in the asymptotic limit of large wavelengths (in comparison to the correlation scale of convection), to characterize the effect of small-scale surface convection on resonant-mode frequencies in the Sun. We show that the full oscillation equations, in the presence of temporally stationary 3-D flows, can be reduced to an effective "quiet-Sun" wave equation with altered sound speed, Br\"{u}nt--V\"{a}is\"{a}la frequency and Lamb frequency. We derive the modified equation and relations for the appropriate averaging of three dimensional flows and thermal quantities to obtain the properties of this effective medium. Using flows obtained from three dimensional numerical simulations of near-surface convection, we quantify their effect on solar oscillation frequencies, and find that they are shifted systematically and substantially. We argue therefore that consistent interpretations of resonant frequencies must include modifications to the wave equation that effectively capture the impact of vigorous hydrodynamic convection.
We present near-infrared emission-line flux distributions, excitation and kinematics, as well as stellar kinematics, of the inner 520x520 pc2$ of the Seyfert 2 galaxy NGC5929. The observations were performed with the Gemini's Near-Infrared Integral Field Spectrograph (NIFS) at a spatial resolution of 20 pc and spectral resolution of 40km/s in the J- and K-bands. The flux distributions of H2, [FeII], [PII] and recombination lines are extended over most of the field of view, with the highest intensity levels observed along PA=60/240deg, and well correlated with the radio emission. The H2 and [FeII] line emission are originated in thermal processes, mainly due to heating of the gas by X-rays from the central Active Galactic Nucleus (AGN). Contribution of shocks due to the radio jet is observed at locations co-spatial with the radio hotspots at 0.5" northeast and 0.6" southwest of the nucleus, as evidenced by the emission-line ratio and gas kinematics. The stellar kinematics shows rotation with an amplitude at 250pc from the nucleus of 200 km/s after corrected for the inferred inclination of 18.3deg. The stellar velocity dispersion obtained from the integrated K-band spectrum is sigma*=133+/-8 km/s, which implying on a mass for the supermassive black hole of M=5.2E7 Msun, using the M-sigma* relation. The gas kinematics present three components: (1) gas in the plane of the galaxy in counter-rotation relative to the stars; (2) an outflow perpendicular to the radio jet that seems to be due to an equatorial AGN outflow; (3) turbulence of the gas observed in association with the radio hot spots, supporting an interaction of the radio jet with the gas of the disk. We estimated the mass of ionized and warm molecular gas of ~1.3E6 Msun and ~470 Msun, respectively.
The large separations between the oscillation frequencies of solar-like stars are measures of stellar mean density. The separations have been thought to be mostly constant in the observed range of frequencies. However, detailed investigation shows that they are not constant, and their variations are not random but have very strong diagnostic potential for our understanding of stellar structure and evolution. In this regard, frequencies of the minimum large separation are very useful tools. From these frequencies, in addition to the large separation and frequency of maximum amplitude, Y\i ld\i z et al. recently have developed new methods to find almost all the fundamental stellar properties. In the present study, we aim to find metallicity and helium abundances from the frequencies, and generalize the relations given by Y\i ld\i z et al. for a wider stellar mass range and arbitrary metallicity ($Z$) and helium abundance ($Y$). We show that the effect of metallicity is { significant} for most of the fundamental parameters. For stellar mass, for example, the expression must be multiplied by $(Z/Z_{\sun})^{0.12}$. For arbitrary helium abundance, $ M \propto (Y/Y_{\sun})^{0.25} $. Methods for determination of $Z$ and $Y$ from pure asteroseismic quantities are based on amplitudes (differences between maximum and minimum values of \Dnu) in the oscillatory component in the spacing of oscillation frequencies. Additionally, we demonstrate that the difference between the first maximum and the second minimum is very sensitive to $Z$. It also depends on $\nu_{\rm min1}/\nu_{\rm max}$ and small separation between the frequencies. Such a dependence leads us to develop a method to find $Z$ (and $Y$) from oscillation frequencies. The maximum difference between the estimated and model $Z$ values is about 14 per cent. It is 10 per cent for $Y$.
We have mapped the superwind/halo region of the nearby starburst galaxy M82 in the mid-infrared with $Spitzer-IRS$. The spectral regions covered include the H$_2 S(1)-S(3)$, [NeII], [NeIII] emission lines and PAH features. We estimate the total warm H$_2$ mass and the kinetic energy of the outflowing warm molecular gas to be between $M_{warm}\sim5-17\times10^6$ M$_{\odot}$ and $E_{K}\sim6-20\times10^{53}$ erg. Using the ratios of the 6.2, 7.7 and 11.3 micron PAH features in the IRS spectra, we are able to estimate the average size and ionization state of the small grains in the superwind. There are large variations in the PAH flux ratios throughout the outflow. The 11.3/7.7 and the 6.2/7.7 PAH ratios both vary by more than a factor of five across the wind region. The Northern part of the wind has a significant population of PAH's with smaller 6.2/7.7 ratios than either the starburst disk or the Southern wind, indicating that on average, PAH emitters are larger and more ionized. The warm molecular gas to PAH flux ratios (H$_2/PAH$) are enhanced in the outflow by factors of 10-100 as compared to the starburst disk. This enhancement in the H$_2/PAH$ ratio does not seem to follow the ionization of the atomic gas (as measured with the [NeIII]/[NeII] line flux ratio) in the outflow. This suggests that much of the warm H$_2$ in the outflow is excited by shocks. The observed H$_2$ line intensities can be reproduced with low velocity shocks ($v < 40$ km s$^{-1}$) driven into moderately dense molecular gas ($10^2 <n_H < 10^4$ cm$^{-3}$) entrained in the outflow.
Elemental abundance patterns in the Galactic disk constrain theories of the formation and evolution of the Milky Way. HII region abundances are the result of billions of years of chemical evolution. We made radio recombination line and continuum measurements of 21 HII regions located between Galactic azimuth Az = 90-130 degree, a previously unexplored region. We derive the plasma electron temperatures using the line-to-continuum ratios and use them as proxies for the nebular [O/H] abundances, because in thermal equilibrium the abundance of the coolants (O, N, and other heavy elements) in the ionized gas sets the electron temperature, with high abundances producing low temperatures. Combining these data with our previous work produces a sample of 90 HII regions with high quality electron temperature determinations. We derive kinematic distances in a self-consistent way for the entire sample. The radial gradient in [O/H] is -0.082 +/- 0.014 dex/kpc for Az = 90-130 degree, about a factor of two higher than the average value between Az = 0-60 degree. Monte Carlo simulations show that the azimuthal structure we reported for Az = 0-60 degree is not significant because kinematic distance uncertainties can be as high as 50% in this region. Nonetheless, the flatter radial gradients between Az = 0-60 degree compared with Az = 90-130 degree, are significant within the uncertainty. We suggest that this may be due to radial mixing from the Galactic Bar whose major axis is aligned toward Az ~30 degree.
We present optimal quadratic estimators for the Fourier analysis of cosmological surveys that detect several different types of tracers of large-scale structure. Our estimators can be used to simultaneously fit the matter power spectrum and the biases of the tracers - as well as redshift-space distortions (RSDs), non-Gaussianities (NGs), or any other effects that are manifested through differences between the clusterings of distinct species of tracers. Our estimators reduce to the one by Feldman, Kaiser & Peacock (ApJ 1994, FKP) in the case of a survey consisting of a single species of tracer. We show that the multi-tracer estimators are unbiased, and that their covariance is given by the inverse of the multi-tracer Fisher matrix (Abramo, MNRAS 2013; Abramo & Leonard, MNRAS 2013). When the biases, RSDs and NGs are fixed to their fiducial values, and one is only interested in measuring the underlying power spectrum, our estimators are projected into the estimator found by Percival, Verde & Peacock (MNRAS 2003). We have tested our estimators on simple (lognormal) simulated galaxy maps, and we show that it performs as expected, being either equivalent or superior to the FKP method in all cases we analyzed. Finally, we have shown how to extend the multi-tracer technique to include the 1-halo term of the power spectrum.
Observations on the high-redshift galaxies at $z>6$ imply that their ionizing emissivity is unable to fully reionize the Universe at $z\sim 6$. Either a high escape fraction of ionizing photons from these galaxies or a large population of faint galaxies below the detection limit are required. However, these requirements are somewhat in tension with present observations. In this work, we explored the combined contribution of mini-quasars and stars to the reionization of cosmic hydrogen and helium. Our model is roughly consistent with: (1) the low escape fractions of ionizing photons from the observed galaxies, (2) the optical depth of Cosmic Microwave Background (CMB) measured by the WMAP-7, and (3) the redshift of the end of hydrogen and helium reionization at $z\approx 6$ and $z\approx 3$, respectively. Neither an extremely high escape fraction nor a large population of fainter galaxies is required in this scenario. In our most optimistic model, more than $\sim20\%$ of the cosmic helium is reionized by $z\sim6$, and the ionized fraction of cosmic helium rapidly climbs to more than $50\%$ by $z\sim5$. These results may imply that better measurements of helium reionization, especially at high redshifts, could be helpful in constraining the growth of intermediate-mass black holes (IMBHs) in the early Universe, which would shed some light on the puzzles concerning the formation of supermassive black holes (SMBHs).
The barycenter of a massive black hole binary will lie outside the event horizon of the primary black hole for modest values of mass ratio and binary separation. Analagous to radial velocity shifts in stellar emission lines caused by the tug of planets, the radial velocity of the primary black hole around the barycenter can leave a tell-tale oscillation in the broad component of Fe K$\alpha$ emission from accreting gas. Near-future X-ray telescopes such as Astro-H and Athena will have the energy resolution ($\delta E/E \lesssim 10^{-3}$) to search nearby active galactic nuclei (AGN) for the presence of binaries with mass ratios $q \gtrsim 0.01$, separated by several hundred gravitational radii. The general-relativistic and Lense-Thirring precession of the periapse of the secondary orbit imprints a detectable modulation on the oscillations. The lowest mass binaries in AGN will oscillate many times within typical X-ray exposures, leading to a broadening of the line wings and an over-estimate of black hole spin in these sources. Detection of periodic oscillations in the AGN line centroid energy will reveal a massive black hole binary close to merger and will provide an early warning of gravitational radiation emission.
In our recent paper, we argued that the broad hydrogen lines, as well as the low-ionization lines in quasars, are significantly contributed by the Cerenkov quasi-line emission of the fast electrons in the dense clouds/filaments/sheets ($N_{\rm H}\geq 10^{14}~{\rm cm^{-3}}$); whereas this line-like radiation mechanism is invalid for producing the high ionization lines. Therefore, the observed broad hydrogen lines or low-ionization lines should be blended by both the real line emission via the bound-bound transition in atoms/ions and the Cerenkov quasi-line emission. In this paper, we provide an evidence quantitatively supporting above conclusions. Until now the observed different redshifts of different broad hydrogen lines is still a problem at issue. The Cerenkov line-like radiation mechanism provides a plausible resolution for this difficulty: it is the `Cerenkov line redshift', which is different from line to line, causes the peculiar redshift-differences among Ly$\alpha$, H$\alpha$ and H$\beta$ lines. The good fitting to the observed redshifts of quasars confirms the existence of Cerenkov component in the broad hydrogen lines. Furthermore, we conclude that, in the blended Ly$\alpha$ line, the line-intensity of the Cerenkov component approximately equals that of the accompanying `normal line' (an approximate equipartition of intensity between the two components in the broad Ly$\alpha$ line). This result quantitatively illustrates the importance of the Cerenkov component in the broad lines of quasars.
Analysis of new radial velocity measurements of the active giant PZ Mon is presented. We estimated the radial velocity of center of mass 25.5$\pm$0.3 km s$^{-1}$, the period on the circular orbit $P=34.14\pm0.02$ days, and parameters of the secondary component including the mass $M_2$=0.14 M$_\odot$ which is a smallest among known components of RS CVn type giants. Combined with photometric data we conclude that PZ Mon is a system with synchronous rotation, and there is a big cool spotted area on PZ Mon surface towards to secondary component that provides optical variability.
We present in this paper a new Bayesian semi-blind approach for foreground removal in observations of the 21-cm signal with interferometers. The technique, which we call HIEMICA (HI Expectation-Maximization Independent Component Analysis), is an extension of the Independent Component Analysis (ICA) technique developed for two-dimensional (2D) CMB maps to three-dimensional (3D) 21-cm cosmological signals measured by interferometers. This technique provides a fully Bayesian inference of power spectra and maps and separates the foregrounds from signal based on the diversity of their power spectra. Only relying on the statistical independence of the components, this approach can jointly estimate the 3D power spectrum of the 21-cm signal and, the 2D angular power spectrum and the frequency dependence of each foreground component, without any prior assumptions about foregrounds. This approach has been tested extensively by applying it to mock data from interferometric 21-cm intensity mapping observations. Based on the Expectation-Maximization (EM) algorithm, this blind approach provides much better recovery of the 21-cm power spectrum over all scales than the commonly used Principal Component Analysis (PCA). This technique can be applied straightforwardly to all 21-cm interferometric observations, including epoch of reionization measurements, and can be extended to single-dish observations as well.
The hydrogen-deficient, carbon-rich R Coronae Borealis (RCB) stars are known for being prolific producers of dust which causes their large iconic declines in brightness. Several RCB stars, including R CrB, itself, have large extended dust shells seen in the far-infrared. The origin of these shells is uncertain but they may give us clues to the evolution of the RCB stars. The shells could form in three possible ways. 1) they are fossil Planetary Nebula (PN) shells, which would exist if RCB stars are the result of a final, helium-shell flash, 2) they are material left over from a white-dwarf merger event which formed the RCB stars, or 3) they are material lost from the star during the RCB phase. Arecibo 21-cm observations establish an upper limit on the column density of H I in the R CrB shell implying a maximum shell mass of $\lesssim$0.3 M$_{\odot}$. A low-mass fossil PN shell is still a possible source of the shell although it may not contain enough dust. The mass of gas lost during a white-dwarf merger event will not condense enough dust to produce the observed shell, assuming a reasonable gas-to-dust ratio. The third scenario where the shell around R CrB has been produced during the star's RCB phase seems most likely to produce the observed mass of dust and the observed size of the shell. But this means that R CrB has been in its RCB phase for $\sim$10$^{4}$ yr.
Buchdahl, by imposing a few physical assumptions on the matter, i.e., its density is a nonincreasing function of the radius and the fluid is a perfect fluid, and on the configuration, such as the exterior is the Schwarzschild solution, found that the radius $r_0$ to mass $m$ ratio of a star would obey the Buchdahl bound $r_0/m\geq9/4$. He noted that the bound was saturated by the Schwarzschild interior solution, the solution with $\rho_{\rm m}(r)= {\rm constant}$, where $\rho_{\rm m}(r)$ is the energy density of the matter at $r$, when the central central pressure blows to infinity. Generalizations of this bound have been studied. One generalization was given by Andr\'easson by including electrically charged matter and imposing that $p+2p_T \leq\rho_{\rm m}$, where $p$ is the radial pressure and $p_T$ the tangential pressure. His bound is given by $r_0/m\geq9/\left(1+\sqrt{1+3\,q^2/r_0^2}\right)^{2}$, the Buchdahl-Andr\'easson bound, with $q$ being the star's total electric charge. Following Andr\'easson's proof, the configuration that saturates the Buchdahl bound is an uncharged shell, rather than the Schwarzschild interior solution. By extension, the configurations that saturate the Buchdahl-Andr\'easson bound are charged shells. One expects then, in turn, that there should exist an electrically charged equivalent to the interior Schwarzschild limit. We find here that this equivalent is provided by the equation $\rho_{\rm m}(r) + {Q^2(r)}/ {\left(8\pi\,r^4\right)}= {\rm constant}$, where $Q(r)$ is the electric charge at $r$. This equation was put forward by Cooperstock and de la Cruz, and Florides, and realized in Guilfoyle's stars. When the central pressure goes to infinity Guilfoyle's stars are configurations that saturate the Buchdahl-Andr\'easson bound. It remains to find a proof in Buchdahl's manner such that these configurations are the limiting configurations of the bound.
Not much by themselves, aparently.
We try to reconstruct the scale factor $a(t)$ of the universe from the SNe Ia
data, i.e. the luminosity distance $d_{L}(z)$, using only the cosmological
principle and the assumption that gravitation is governed by a metric theory.
In our hence "model-independent," or "cosmographic" study, we fit functions to
$d_{L}(z)$ rather than $a(t)$, since $d_{L}(z)$ is what is measured. We find
that the acceleration history of the universe cannot be reliably determined in
this approach due to the irregularity and parametrization-dependence of the
results.
However, adding the GRB data to the dataset cures most of the irregularities,
at the cost of compromising the model-independent nature of the study slightly.
Then we can determine the redshift of transition to cosmic acceleration as
$z_{\rm t} \sim 0.50 \pm 0.09$ for a flat universe (larger for positive spatial
curvature).
If Einstein gravity (GR) is assumed, we find a redshift at which the density
of the universe predicted from the $d_{L}(z)$ data is independent of curvature.
We use this point to derive an upper limit on matter density, hence a lower
limit on the density of dark energy. While these limits do not improve the
generally accepted ones, they are derived *only using the $d_{L}(z)$ data*.
It is known that some cosmological perturbations are conformal invariant. This facilitates the studies of perturbations within some gravitational theories alternative to general relativity, for example the scalar-tensor theory, because it is possible to do equivalent analysis in a certain frame in which the perturbation equations are simpler. In this paper we revisit the problem of conformal invariances of cosmological perturbations in terms of the covariant approach in which the perturbation variables have clear geometric and physical meanings. We show that with this approach the conformal invariant perturbations are easily identified.
We analyze the parametric space of the constrained minimal supersymmetric standard model (CMSSM) with mu>0 supplemented by a generalized asymptotic Yukawa coupling quasi-unification condition which yields acceptable masses for the fermions of the third family. We impose constraints from the cold dark matter abundance in the universe and its direct detection experiments, the B-physics, as well as the masses of the sparticles and the lightest neutral CP-even Higgs boson, m_h. We identify two distinct allowed regions with M_{1/2}>m_0 and m_0>>M_{1/2} classified in the hyperbolic branch of the radiative electroweak symmetry breaking. In the first region we obtain, approximately, 44<=tan beta<=52, -3<=A_0/M_{1/2}<=0.1, 122<=m_h/GeV<=127, and mass of the lightest sparticle in the range (0.75-1.43) TeV. Such heavy lightest sparticle masses can become consistent with the cold dark matter requirement on the lightest sparticle relic density thanks to neutralino-stau coannihilations. In the latter region, fixing m_h to its central value from the LHC, we find a wider allowed parameter space with milder electroweak-symmetry-breaking fine-tuning, 40<=tanbeta<=50, -11<=A_0/M_{1/2}<=15 and mass of the lightest sparticle in the range (0.09-1.1) TeV. This sparticle is possibly detectable by the present cold dark matter direct search experiments.
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Context. At least 492 central stars of Galactic planetary nebulae (CSPNs)
have been assigned spectral types. Since many CSPNs are faint, these
classification efforts are frequently made at low spectral resolution. However,
the stellar Balmer absorption lines are contaminated with nebular emission;
therefore in many cases a low-resolution spectrum does not enable the
determination of the H abundance in the CSPN photosphere. Whether or not the
photosphere is H deficient is arguably the most important fact we should expect
to extract from the CSPN spectrum, and should be the basis for an adequate
spectral classification system.
Aims. Our purpose is to provide accurate spectral classifications and
contribute to the knowledge of central stars of planetary nebulae and stellar
evolution.
Methods. We have obtained and studied higher quality spectra of CSPNs
described in the literature as weak emission-line star (WELS). We provide
descriptions of 19 CSPN spectra. These stars had been previously classified at
low spectral resolution. We used medium-resolution spectra taken with the
Gemini Multi-Object Spectrograph (GMOS). We provide spectral types in the
Morgan-Keenan (MK) system whenever possible.
Results. Twelve stars in our sample appear to have normal H rich photospheric
abundances, and five stars remain unclassified. The rest (two) are most
probably H deficient. Of all central stars described by other authors as WELS,
we find that at least 26% of them are, in fact, H rich O stars, and at least 3%
are H deficient. This supports the suggestion that the denomination WELS should
not be taken as a spectral type, because, as a WELS based on low-resolution
spectra, it cannot provide enough information about the photospheric H
abundance.
Thermal mid-infrared emission of quasars requires an obscuring structure that can be modeled as a magneto-hydrodynamic wind in which radiation pressure on dust shapes the outflow. We have taken the dusty wind models presented by Keating and collaborators that generated quasar mid-infrared spectral energy distributions (SEDs), and explored their properties (such as geometry, opening angle, and ionic column densities) as a function of Eddington ratio and X-ray weakness. In addition, we present new models with a range of magnetic field strengths and column densities of the dust-free shielding gas interior to the dusty wind. We find this family of models -- with input parameters tuned to accurately match the observed mid-IR power in quasar SEDs -- provides reasonable values of the Type 1 fraction of quasars and the column densities of warm absorber gas, though it does not explain a purely luminosity-dependent covering fraction for either. Furthermore, we provide predictions of the cumulative distribution of E(B-V) values of quasars from extinction by the wind and the shape of the wind as imaged in the mid-infrared. Within the framework of this model, we predict that the strength of the near-infrared bump from hot dust emission will be correlated primarily with L/L_Edd rather than luminosity alone, with scatter induced by the distribution of magnetic field strengths. The empirical successes and shortcomings of these models warrant further investigations into the composition and behaviour of dust and the nature of magnetic fields in the vicinity of actively accreting supermassive black holes.
It is widely accepted that cosmic rays (CRs) up to at least PeV energies are Galactic in origin. Accelerated particles are injected into the interstellar medium where they propagate to the farthest reaches of the Milky Way, including a surrounding halo. The composition of CRs coming to the solar system can be measured directly and has been used to infer the details of CR propagation that are extrapolated to the whole Galaxy. In contrast, indirect methods, such as observations of gamma-ray emission from CR interactions with interstellar gas, have been employed to directly probe the CR densities in distant locations throughout the Galactic plane. In this article we use 73 months of data from the Fermi Large Area Telescope in the energy range between 300 MeV and 10 GeV to search for gamma-ray emission produced by CR interactions in several high- and intermediate-velocity clouds located at up to ~ 7 kpc above the Galactic plane. We achieve the first detection of intermediate-velocity clouds in gamma rays and set upper limits on the emission from the remaining targets, thereby tracing the distribution of CR nuclei in the halo for the first time. We find that the gamma-ray emissivity per H atom decreases with increasing distance from the plane at 97.5% confidence level. This corroborates the notion that CRs at the relevant energies originate in the Galactic disk. The emissivity of the upper intermediate-velocity Arch hints at a 50% decline of CR densities within 2 kpc from the plane. We compare our results to predictions of CR propagation models.
X-ray flares were discovered in the afterglow phase of gamma-ray bursts (GRBs) by the {\em Swift} satellite a decade ago and known as a canonical component in GRB X-ray afterglows. In this paper, we constrain the Lorentz factors of GRB X-ray flares using two different methods. For the first method, we estimate the lower limit on the bulk Lorentz factor with the flare duration and jet break time. In the second method, the upper limit on the Lorentz factor is derived by assuming that the X-ray flare jet has undergone saturated acceleration. We also re-estimate the initial Lorentz factor with GRB afterglow onsets, and find the coefficient of the theoretical Lorentz factor is 1.67 rather than the commonly used 2 for interstellar medium (ISM) and 1.44 for the wind case. We find that the correlation between the limited Lorentz factor and the isotropic radiation energy of X-ray flares in the ISM case is more consistent with that of prompt emission than the wind case in a statistical sense. For a comparison, the lower limit on Lorentz factor is statistically larger than the extrapolation from prompt bursts in the wind case. Our results indicate that X-ray flares and prompt bursts are produced by the same physical mechanism.
We designed and built a new astronomical photo-polarimeter that can measure linear polarization simultaneously in three spectral bands. It has a Calcite beamdisplacement prism as the analyzer. The ordinary and extra-ordinary emerging beams in each spectral bands are quasi-simultaneously detected by the same photomultiplier by using a high speed rotating chopper. A rotating superachromatic Pancharatnam halfwave plate is used to modulate the light incident on the analyzer. The spectral bands are isolated using appropriate dichroic and glass filters. We show that the reduction of 50% in the efficiency of the polarimeter because of the fact that the intensities of the two beams are measured alternately is partly compensated by the reduced time to be spent on the observation of the sky background. The use of a beam-displacement prism as the analyzer completely removes the polarization of background skylight, which is a major source of error during moonlit nights, especially, in the case of faint stars. The field trials that were carried out by observing several polarized and unpolarized stars show the performance of the polarimeter to be satisfactory.
We extract the resonant orbits from an N-body bar that is a good representation of the Milky Way, using the method recently introduced by Molloy et al. (2015). By decomposing the bar into its constituent orbit families, we show that they are intimately connected to the boxy-peanut shape of the density. We highlight the imprint due solely to resonant orbits on the kinematic landscape towards the Galactic centre. The resonant orbits are shown to have distinct kinematic features and may be used to explain the cold velocity peak seen in the APOGEE commissioning data (Nidever et al. 2012). We show that high velocity peaks are a natural consequence of the motions of stars in the 2:1 orbit family. The locations of the peaks vary with bar angle and, with the tacit assumption that the observed peaks are due to the 2:1 family, we find that the locations of the high velocity peaks correspond to bar angles in the range 10 < theta_bar < 25 (deg). However, some important questions about the nature of the peaks remain, such as their apparent absence in other surveys of the Bulge and the deviations from symmetry between equivalent fields in the north and south.
We describe a new iteration method to estimate asteroid coordinates, which is
based on the subpixel Gaussian model of a discrete object image. The method
operates by continuous parameters (asteroid coordinates) in a discrete
observational space (the set of pixels potential) of the CCD frame. In this
model, a kind of the coordinate distribution of the photons hitting a pixel of
the CCD frame is known a priori, while the associated parameters are determined
from a real digital object image. The developed method, being more flexible in
adapting to any form of the object image, has a high measurement accuracy along
with a low calculating complexity due to a maximum likelihood procedure, which
is implemented to obtain the best fit instead of a least-squares method and
Levenberg-Marquardt algorithm for the minimisation of the quadratic form.
Since 2010, the method was tested as the basis of our CoLiTec (Collection
Light Technology) software, which has been installed at several observatories
of the world with the aim of automatic discoveries of asteroids and comets on a
set of CCD frames. As the result, four comets (C/2010 X1 (Elenin), P/2011
NO1(Elenin), C/2012 S1 (ISON), and P/2013 V3 (Nevski)) as well as more than
1500 small Solar System bodies (including five NEOs, 21 Trojan asteroids of
Jupiter, and one Centaur object) were discovered. We discuss these results that
allowed us to compare the accuracy parameters of a new method and confirm its
efficiency.
In 2014, the CoLiTec software was recommended to all members of the
Gaia-FUN-SSO network for analysing observations as a tool to detect faint
moving objects in frames.
How rapidly collapsing parsec-scale massive molecular clumps feed high-mass stars, and how they fragment to form OB clusters, have been outstanding questions in the field of star-formation. In this work, we report the resolved structures and kinematics of the approximately face-on, rotating massive molecular clump, G33.92+0.11. Our high resolution Atacama Large Millimeter/submillimeter Array (ALMA) images show that the spiral arm-like gas overdensities form in the eccentric gas accretion streams. First, we resolved that the dominant part of the $\sim$0.6 pc scale massive molecular clump (3.0$^{+2.8}_{-1.4}$$\cdot$10$^{3}$ $M_{\odot}$) G33.92+0.11 A is tangled with several 0.5-1 pc size molecular arms spiraling around it, which may be connected further to exterior gas accretion streams. Within G33.92+0.11 A, we resolved the $\sim$0.1 pc width gas mini-arms connecting with the two central massive (100-300 $M_{\odot}$) molecular cores. The kinematics of arms and cores elucidate a coherent accretion flow continuing from large to small scales. We demonstrate that the large molecular arms are indeed the cradles of dense cores, which are likely current or future sites of high-mass star formation. Since these deeply embedded massive molecular clumps preferentially form the highest mass stars in the clusters, we argue that dense cores fed by or formed within molecular arms play a key role in making the upper end of the stellar and core mass functions.
We explore a diffusive shock acceleration (DSA) model for radio relics in which a spherical shock impinges on a magnetized cloud of fossil relativistic electrons in the cluster periphery. Such a scenario could explain uniformity of the surface brightness and spectral curvature in the integrated spectra of thin arc-like radio relics. Toward this end, we perform DSA simulations of spherical shocks with the parameters relevant for the Sausage radio relic in cluster CIZA J2242.8+5301, and calculate the ensuing radio synchrotron emission from re-accelerated electrons. The surface brightness profile of radio-emitting postshock region and the volume-integrated radio spectrum are calculated as well. We find that the observed width of the Sausage relic can be explained reasonably well by shocks with speed $u_s \sim 3,000 \kms$ and sonic Mach number $M_s \sim 3$. These shocks produce curved radio spectra that steepen gradually over $(0.1-10) \nu_{\rm br}$ with break frequency $ \nu_{\rm br}\sim 1$ GHz, if the duration of electron acceleration is $\sim 60 - 80$ Myr. However, the abrupt increase of spectral index above $\sim 1.5$ GHz observed in the Sausage relic seems to indicate that additional physical processes, other than radiative losses, operate for electrons with $\gamma_e \gtrsim 10^4$.
Semi-regular (SR) variables are not a homogeneous class and their variability
is often explained due to pulsations and/or binarity. This study focuses on
IRAS 19135+3937, an SRd variable with an infra-red excess indicative of a dusty
disc. A time-series of high-resolution spectra, UBV photometry as well as a
very accurate light curve obtained by the Kepler satellite, allowed us to study
the object in unprecedented detail. We discovered it to be a binary with a
period of 127 days. The primary has a low surface gravity and an atmosphere
depleted in refractory elements. This combination of properties unambiguously
places IRAS 19135+3937 in the subclass of post-Asymptotic Giant Branch stars
with dusty discs.
We show that the light variations in this object can not be due to
pulsations, but are likely caused by the obscuration of the primary by the
circumbinary disc during orbital motion. Furthermore, we argue that the
double-peaked Fe emission lines provide evidence for the existence of a gaseous
circumbinary Keplerian disc inside the dusty disc. A secondary set of
absorption lines has been detected near light minimum, which we attribute to
the reflected spectrum of the primary on the disc wall, which segregates due to
the different Doppler shift. This corroborates the recent finding that
reflection in the optical by this type of discs is very efficient. The system
also shows a variable Halpha profile indicating a collimated outflow
originating around the companion. IRAS 19135+3937 thus encompasses all the
major emergent trends about evolved disc systems, that will eventually help to
place these objects in the evolutionary context.
MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is an integral-field spectroscopic survey of 10,000 nearby galaxies that is one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV). MaNGA's 17 pluggable optical fiber-bundle integral field units (IFUs) are deployed across a 3 deg field, they yield spectral coverage 3600-10,300 Ang at a typical resolution R ~ 2000, and sample the sky with 2" diameter fiber apertures with a total bundle fill factor of 56%. Observing over such a large field and range of wavelengths is particularly challenging for obtaining uniform and integral spatial coverage and resolution at all wavelengths and across each entire fiber array. Data quality is affected by the IFU construction technique, chromatic and field differential refraction, the adopted dithering strategy, and many other effects. We use numerical simulations to constrain the hardware design and observing strategy for the survey with the aim of ensuring consistent data quality that meets the survey science requirements while permitting maximum observational flexibility. We find that MaNGA science goals are best achieved with IFUs composed of a regular hexagonal grid of optical fibers with rms displacement of 5 microns or less from their nominal packing position, this goal is met by the MaNGA hardware, which achieves 3 microns rms fiber placement. We further show that MaNGA observations are best obtained in sets of three 15-minute exposures dithered along the vertices of a 1.44 arcsec equilateral triangle, these sets form the minimum observational unit, and are repeated as needed to achieve a combined signal-to-noise ratio of 5 per Angstrom per fiber in the r-band continuum at a surface brightness of 23 AB/arcsec^2. (abbrev.)
This is the first version (v1) of the Gravitational LENses and DArk MAtter (GLENDAMA) database accessible at this http URL The new database contains more than 6000 ready-to-use (processed) astronomical frames corresponding to 15 objects that fall into three classes: (1) lensed QSO (8 objects), (2) binary QSO (3 objects), and (3) accretion-dominated radio-loud QSO (4 objects). Data are also divided into two categories: freely available and available upon request. The second category includes observations related to our yet unpublished analyses. Although this v1 of the GLENDAMA archive incorporates an X-ray monitoring campaign for a lensed QSO in 2010, the rest of frames (imaging, polarimetry and spectroscopy) were taken with NUV, visible and NIR facilities over the period 1999$-$2014. The monitorings and follow-up observations of lensed QSOs are key tools for discussing the accretion flow in distant QSOs, the redshift and structure of intervening (lensing) galaxies, and the physical properties of the Universe as a whole.
With the use of a background Milky-Way-like potential model, we performed stellar orbital and magnetohydrodynamic (MHD) simulations. As a first experiment, we studied the gaseous response to a bisymmetric spiral arm potential: the widely employed cosine potential model and a self-gravitating tridimensional density distribution based model called PERLAS. Important differences are noticeable in these simulations, while the simplified cosine potential produces two spiral arms for all cases, the more realistic density based model produces a response of four spiral arms on the gaseous disk, except for weak arms -i.e. close to the linear regime- where a two-armed structure is formed. In order to compare the stellar and gas response to the spiral arms, we have also included a detailed periodic orbit study and explored different structural parameters within observational uncertainties. The four armed response has been explained as the result of ultra harmonic resonances, or as shocks with the massive bisymmetric spiral structure, among other. From the results of this work, and comparing the stellar and gaseous responses, we tracked down an alternative explanation to the formation of branches, based only on the orbital response to a self-gravitating spiral arms model. The presence of features such as branches, might be an indication of transiency of the arms.
We present 2 - 5 micron adaptive optics (AO) imaging and polarimetry of the famous hypergiant stars IRC +10420 and VY Canis Majoris. The imaging polarimetry of IRC +10420 with MMT-Pol at 2.2 micron resolves nebular emission with intrinsic polarization of 30%, with a high surface brightness indicating optically thick scattering. The relatively uniform distribution of this polarized emission both radially and azimuthally around the star confirms previous studies that place the scattering dust largely in the plane of the sky. Using constraints on scattered light consistent with the polarimetry at 2.2 micron, extrapolation to wavelengths in the 3 - 5 micron band predicts a scattered light component significantly below the nebular flux that is observed in our LBT/LMIRCam 3 - 5 micron AO imaging. Under the assumption this excess emission is thermal, we find a color temperature of ~ 500 K is required, well in excess of the emissivity-modified equilibrium temperature for typical astrophysical dust. The nebular features of VY CMa are found to be highly polarized (up to 60%) at 1.3 micron, again with optically thick scattering required to reproduce the observed surface brightness. This star's peculiar nebular feature dubbed the "Southwest Clump" is clearly detected in the 3.1 micron polarimetry as well, which, unlike IRC+10420, is consistent with scattered light alone. The high intrinsic polarizations of both hypergiants' nebulae are compatible with optically thick scattering for typical dust around evolved dusty stars, where the depolarizing effect of multiple scatters is mitigated by the grains' low albedos.
The 2:1 mean-motion resonance with Jupiter harbours two distinct groups of
asteroids. The short-lived population is known to be a transient group
sustained in steady state by the Yarkovsky semimajor axis drift. The long-lived
asteroids, however, can exhibit dynamical lifetimes comparable to
$4\,\mathrm{Gyr}$. They reside near two isolated islands of the phase space
denoted $\mathrm{A}$ and $\mathrm{B}$, with an uneven population ratio
$\mathrm{B}/\mathrm{A} \simeq 10$. The orbits of $\mathrm{A}$-island asteroids
are predominantly highly inclined, compared to island $\mathrm{B}$. The
size-frequency distribution is steep but the orbital distribution lacks any
evidence of a collisional cluster. These observational constraints are somewhat
puzzling and therefore the origin of the long-lived asteroids has not been
explained so far.
With the aim to provide a viable explanation, we first update the resonant
population and revisit its physical properties. Using an $N$-body model with
seven planets and the Yarkovsky effect included, we demonstrate that the
dynamical depletion of island $\mathrm{A}$ is faster, in comparison with island
$\mathrm{B}$. Then we investigate (i) the survivability of primordial resonant
asteroids and (ii) capture of the population during planetary migration,
following a recently described scenario with an escaping fifth giant planet and
a jumping-Jupiter instability. We also model the collisional evolution of the
resonant population over past $4\,\mathrm{Gyr}$. Our conclusion is that the
long-lived group was created by resonant capture from a narrow part of
hypothetical outer main-belt family during planetary migration. Primordial
asteroids surviving the migration were probably not numerous enough to
substantially contribute to the observed population.
By careful searching of synthetic and observed spectra in a sample of cool giant and supergiant stars, we have updated the continuum band-passes of near-infrared Wing three filter system. This photometric system measures the strength of Titanium Oxide (TiO) absorption in Near-Infrared (NIR) at 719 nm. We show that new reference continuum band-passes are essentially free from molecular absorptions and the updated TiO-index defines the temperature variation in a sample of cool giants with less scatter. A TiO-index vs. effective temperature calibration is derived based on new continuum band-passes.
We report on the SDO/AIA and Hinode/EIS observations of a transient coronal loop. The loop brightens up in the same location after the disappearance of an arcade formed during a B8.9-class microflare three hours earlier. EIS captures this loop during its brightening phase as observed in most of the AIA filters. We use the AIA data to study the evolution of the loop, as well as to perform the DEM diagnostics as a function of $\kappa$. Fe XI--XIII lines observed by EIS are used to perform the diagnostics of electron density and subsequently the diagnostics of $\kappa$. Using ratios involving the Fe XI 257.772\AA selfblend, we diagnose $\kappa$ $\lesssim$ 2, i.e., an extremely non-Maxwellian distribution. Using the predicted Fe line intensities derived from the DEMs as a function of $\kappa$, we show that, with decreasing $\kappa$, all combinations of ratios of line intensities converge to the observed values, confirming the diagnosed $\kappa$ $\lesssim$ 2. These results represent the first positive diagnostics of $\kappa$-distributions in the solar corona despite the limitations imposed by calibration uncertainties.
Using new integral field observations of 106 galaxies in three nearby clusters we investigate how the intrinsic scatter of the Fundamental Plane depends on the way in which the velocity dispersion and effective radius are measured. Our spatially resolved spectroscopy, combined with a cluster sample with negligible relative distance errors allows us to derive a Fundamental Plane with minimal systematic uncertainties. From the apertures we tested, we find that velocity dispersions measured within a circular aperture with radius equal to one effective radius minimises the intrinsic scatter of the Fundamental Plane. Using simple yet powerful Jeans dynamical models we determine dynamical masses for our galaxies. Replacing luminosity in the Fundamental Plane with dynamical mass, we demonstrate that the resulting Mass Plane has further reduced scatter, consistent with zero intrinsic scatter. Using these dynamical models we also find evidence for a possibly non-linear relationship between dynamical mass-to-light ratio and velocity dispersion.
With the use of a detailed Milky Way nonaxisymmetric potential, observationally and dynamically constrained, the e?ects of the bar and the spiral arms in the Galaxy are studied in the disc and in the stellar halo. Especially the trapping of stars in the disc and Galactic halo by resonances on the Galactic plane, induced by the Galactic bar, has been analysed in detail. To this purpose, a new method is presented to delineate the trapping regions using empirical diagrams of some orbital properties obtained in the Galactic potential. In these diagrams we plot in the inertial Galactic frame a characteristic orbital energy versus a characteristic orbital angular momentum, or versus the orbital Jacobi constant in the reference frame of the bar, when this is the only nonaxisymmetric component in the Galactic potential. With these diagrams some trapping regions are obtained in the disc and halo using a sample of disc stars and halo stars in the solar neighbourhood. We compute several families of periodic orbits on the Galactic plane, some associated with this resonant trapping. In particular, we ?nd that the trapping e?ect of these resonances on the Galactic plane can extend several kpc from this plane, trapping stars in the Galactic halo. The purpose of our analysis is to investigate if the trapping regions contain some known moving groups in our Galaxy. We have applied our method to the Kapteyn group, a moving group in the halo, and we have found that this group appears not to be associated with a particular resonance on the Galactic plane.
Palladium (Pd) and silver (Ag) are the key elements for probing the weak component in the rapid neutron-capture process (r-process) of stellar nucleosynthesis. We performed a detailed analysis of the high-resolution and high signal-to-noise ratio near-UV spectra from the archive of HIRES on the Keck telescope, UVES on the VLT, and HDS on the Subaru Telescope, to determine the Pd and Ag abundances of 95 stars. This sample covers a wide metallicity range with -2.6 $\lesssim$ [Fe/H] $\lesssim$ +0.1, and most of them are dwarfs. The plane-parallel LTE MAFAGS-OS model atmosphere was adopted, and the spectral synthesis method was used to derive the Pd and Ag abundances from Pd I {\lambda} 3404 {\AA} and Ag I {\lambda} 3280/3382 {\AA} lines. We found that both elements are enhanced in metal-poor stars, and their ratios to iron show flat trends at -0.6 < [Fe/H] < +0.1. The abundance ratios of [Ag/H] and [Pd/H] are well correlated over the whole abundance range. This implies that Pd and Ag have similar formation mechanisms during the Galactic evolution.
The dynamics of magnetic fields in closed regions of solar and stellar coronae are investigated with a reduced magnetohydrodynamic (MHD) model in the framework of Parker scenario for coronal heating. A novel analysis of reduced MHD equilibria shows that their magnetic fields have an asymmetric structure in the axial direction with variation length-scale $z_\ell \sim \ell B_0/b$, where $B_0$ is the intensity of the strong axial guide field, $b$ that of the orthogonal magnetic field component, and $\ell$ the scale of $\mathbf{b}$. Equilibria are then quasi-invariant along the axial direction for variation scales larger than approximatively the loop length $z_\ell \gtrsim L_z$, and increasingly more asymmetric for smaller variation scales $z_\ell \lesssim L_z$. The $critical$ $length$ $z_\ell \sim L_z$ corresponds to the magnetic field intensity threshold $b \sim \ell B_0/L_z$. Magnetic fields stressed by photospheric motions cannot develop strong axial asymmetries. Therefore fields with intensities below such threshold evolve quasi-statically, readjusting to a nearby equilibrium, without developing nonlinear dynamics nor dissipating energy. But stronger fields cannot access their corresponding asymmetric equilibria, hence they are out-of-equilibrium and develop nonlinear dynamics. The subsequent formation of current sheets and energy dissipation is $necessary$ for the magnetic field to relax to equilibrium, since dynamically accessible equilibria have variation scales larger than the loop length $z_\ell \gtrsim L_z$, with intensities smaller than the threshold $b \lesssim \ell B_0/L_z$. The dynamical implications for magnetic fields of interest to solar and stellar coronae are investigated numerically and the impact on coronal physics discussed.
We report the first results of a programme aimed at studying the properties
of high redshift galaxies with on-going massive and dominant episodes of star
formation (HII galaxies). We use the $L(\mathrm{H}\beta) - \sigma$ distance
estimator based on the correlation between the ionized gas velocity dispersions
and Balmer emission line luminosities of HII galaxies and Giant HII regions to
trace the expansion of the Universe up to $z \sim 2.33$. This approach provides
an independent constraint on the equation of state of dark energy and its
possible evolution with look-back time.
Here we present high-dispersion (8,000 to 10,000 resolution) spectroscopy of
HII galaxies at redshifts between 0.6 and 2.33, obtained at the VLT using
XShooter. Using six of these HII galaxies we obtain broad constraints on the
plane $\Omega_m - w_0$. The addition of 19 high-z HII galaxies from the
literature improves the constraints and highlights the need for high quality
emission line profiles, fluxes and reddening corrections. The 25 high-z HII
galaxies plus our local compilation of 107 HII galaxies up to $z=0.16$ were
used to impose further constraints. Our results are consistent with recent
studies, although weaker due to the as yet small sample and low quality of the
literature data of high-z HII galaxies.
We show that much better and competitive constraints can be obtained using a
larger sample of high redshift HII galaxies with high quality data that can be
easily obtained with present facilities like KMOS at the VLT.
We use the Arepo moving mesh code to simulate the evolution of molecular clouds exposed to a harsh environment similar to that found in the galactic center (GC), in an effort to understand why the star formation efficiency (SFE) of clouds in this environment is so small. Our simulations include a simplified treatment of time-dependent chemistry and account for the highly non-isothermal nature of the gas and the dust. We model clouds with a total mass of 1.3x10^5 M_{sun} and explore the effects of varying the mean cloud density and the virial parameter, alpha = E_{kin}/|E_{pot}|. We vary the latter from alpha = 0.5 to alpha = 8.0, and so many of the clouds that we simulate are gravitationally unbound. We expose our model clouds to an interstellar radiation field (ISRF) and cosmic ray flux (CRF) that are both a factor of 1000 higher than the values found in the solar neighbourhood. As a reference, we also run simulations with local solar neighbourhood values of the ISRF and the CRF in order to better constrain the effects of the extreme conditions in the GC on the SFE. Despite the harsh environment and the large turbulent velocity dispersions adopted, we find that all of the simulated clouds form stars within less than a gravitational free-fall time. Increasing the virial parameter from alpha = 0.5 to alpha = 8.0 decreases the SFE by a factor ~4-10, while increasing the ISRF/CRF by a factor of 1000 decreases the SFE again by a factor ~2-6. However, even in our most unbound clouds, the SFE remains higher than that inferred for real GC clouds. We therefore conclude that high levels of turbulence and strong external heating are not enough by themselves to explain the low SFE at the center of the Galaxy.
Over the last decade there has been immense progress in the follow-up of short and long GRBs, resulting in a significant rise in the detection rate of X-ray and optical afterglows, in the determination of GRB redshifts, and of the identification of the underlying host galaxies. Nevertheless, our theoretical understanding on the progenitors and central engines powering these vast explosions is lagging behind, and a newly identified class of `ultra-long' GRBs has fuelled speculation on the existence of a new channel of GRB formation. In this paper we present high signal-to-noise X-shooter observations of the host galaxy of GRB130925A, which is the fourth unambiguously identified ultra-long GRB, with prompt gamma-ray emission detected for ~20ks. The GRB line of sight was close to the host galaxy nucleus, and our spectroscopic observations cover both this region along the bulge/disk of the galaxy, in addition to a bright star-forming region within the outskirts of the galaxy. From our broad wavelength coverage we obtain accurate metallicity and dust-extinction measurements at both the galaxy nucleus, and outer star-forming region, and measure a super-solar metallicity at both locations, placing this galaxy within the 10-20% most metal-rich GRB host galaxies. Such a high metal enrichment has implications on the progenitor models of both long and ultra-long GRBs, although the edge-on orientation of the host galaxy does not allow us to rule out a large metallicity variation along our line of sight. The spatially resolved spectroscopic data presented in this paper offer important insight into variations in the metal and dust abundance within GRB host galaxies. They also illustrate the need for IFU observations on a larger sample of GRB host galaxies at varies metallicities to provide a more quantitative view on the relation between the GRB circumburst and the galaxy-whole properties.
IceCube has detected the diffuse TeV-PeV neutrino emission, for which the flat spectrum radio quasars (FSRQs) have been proposed to be the strong candidate sources. Here we assume that there is a correlation between the gamma-ray and neutrino fluxes from FSRQs, and use the \textit{Fermi}-LAT detected gamma-ray flux from FSRQs to constrain their neutrino flux, and then test if they can account for the diffuse neutrino emission. We first obtain the gamma-ray/neutrino flux ratio by the diffuse gamma-ray flux from \textit{Fermi}-LAT observations of FSRQs and the diffuse neutrino flux from IceCube detection, then apply this ratio to individual FSRQs, and predict their neutrino flux, to be compared with the upper limits that IceCube provides for individual FSRQs, especially those in the northern sky with more stringent constraint by IceCube. We find that a large fraction of candidate FSRQs from the northern sky in the IceCube point source search has predicted neutrino flux violating the IceCube limit, and in the stacking search the predicted neutrino flux of the FSRQs in the northern sky is close to the current IceCube limit. The sensitivity of IceCube after several years of running time may reach the level that can clearly examine the FSRQ origin of the diffuse neutrino emission. The caveat in the assumptions are also discussed.
We use $N$-body/smoothed particle hydrodynamics simulations of encounters between an early-type galaxy (ETG) and a late-type galaxy (LTG) to study the effects of hot halo gas on the evolution for a case with the mass ratio of the ETG to LTG of 2:1 and the closest approach distance of $\sim$100 kpc. We find that the dynamics of the cold disk gas in the tidal bridge and the amount of the newly formed stars depend strongly on the existence of a gas halo. In the run of interacting galaxies not having a hot gas halo, the gas and stars accreted into the ETG do not include newly formed stars. However, in the run using the ETG with a gas halo and the LTG without a gas halo, a shock forms along the disk gas tidal bridge and induces star formation near the closest approach. The shock front is parallel to a channel along which the cold gas flows toward the center of the ETG. As a result, the ETG can accrete star-forming cold gas and newly born stars at and near its center. When both galaxies have hot gas halos, a shock is formed between the two gas halos somewhat before the closest approach. The shock hinders the growth of the cold gas bridge to the ETG and also ionizes it. Only some of the disk stars transfer through the stellar bridge. We conclude that the hot halo gas can give significant hydrodynamic effects during distant encounters.
We present results from 43 GHz (VLBA, six epochs from 2012.2 to 2013.2) and 86 GHz (GMVA, one epoch in 2012.4) observations toward the basis of the jet in the TeV Blazar Mrk 501. The 43-GHz data analysis reveals a new feature located northeast of the radio core, with a flux density of several tens of mJy, perpendicularly to the jet axis. The 86-GHz image shows the jet feature located 0.75 mas southeast of the radio core, which is consistent with the previous result. The location of Gaussian model for 0.75 mas feature does not coincide with those for the jets in the 43-GHz image, however, a distribution of emission is found. We also discuss the spectral indices of the core, the northeast feature, and the jet feature between 43 GHz and 86 GHz, which show flat-to-steep, steep, and flat-to-invert, respectively.
The wavelength displacement of the Diffuse Interstellar Bands at 4502, 5705, 5780, 6284, and 7224 \AA\ with respect to the well known, narrow atomic/molecular interstellar lines (of Ca{\sc ii} and Na{\sc i}) have been measured in the spectra of the 2 Orion Trapezium stars HD 37022 and HD 37020, using the HARPS\textendash N spectrograph, fed with the 3.5 m Telescopio Nazionale Galileo, and the BOES spectrograph, fed with the 1.8m Korean telescope. The red shift is $\sim$25 km/s for all these DIBs. We discuss the various possible origins of this very peculiar wavelength shift in the light of the particular physical conditions in the Orion Trapezium. The above mentioned shift is seemingly absent in the DIBs at 6196 and 6993 \AA.
We present a non-parametric approach to reconstruct the interaction between dark energy and dark matter directly from SNIa Union 2.1 data using Gaussian Processes, which is a fully Bayesian approach for smoothing data. In this method, once the equation of state ($w$) of dark energy is specified, the interaction can be reconstructed with respect to redshift. For the decaying vacuum energy case with $w=-1$, the reconstructed interaction is consistent with the $\Lambda$CDM model, namely, there is no evidence for the interaction. This also holds for the constant $w$ cases from $-0.9$ to $-1.1$ and for the CPL parameterization case. If the equation of state deviates obviously from $-1$, the reconstructed interaction exits at $95\%$ confidence level. This shows the degeneracy between the interaction and the equation of state of dark energy when they get constraints from the observational data.
Tidal Disruption Events (TDEs) can be perfect probes of dormant SMBHs in normal galaxies. During the rising phase, the accretion luminosity can increase by orders of magnitude in several weeks and the emergent ionizing radiation illuminates the fresh accretion flow. In this paper, we simulated the evolution of the expected spectral line profile of iron due to such a flare by using a ray-tracing code with effects of general relativity (GR) taken into account. We found that the time-dependent profile changes significantly with black hole spin, inclination angle with respect to the black-hole equatorial plane, and the expansion velocity of the ionization front. At low values of spin, a "loop" feature appears in the line profile vs. time plot when the inclination is no less than $30^\circ$ and the expansion velocity $v_{\rm exp}$ is no less than half speed of light, due to a shadow in the emission of the truncated disk. In the light curve two peaks occur depending on the inclination angle. At large $v_{\rm exp}$, a shallow "nose" feature may develop ahead of the loop, its duration depends on the expansion velocity and the inclination angle. We explore the entire interval of black hole spin parameter ranging from extreme prograde to extreme retrograde rotation, $-1<a<1$. In the prograde case, a low-energy tail appears to be more pronounced in the evolving centroid energy of the line. Our results demonstrate the importance to search for X-ray spectral lines in the early phase of TDE flares in order to constrain black hole mass and spin, as well as properties of the innermost accretion flow.
We present the first general circulation model simulations that quantify and reproduce patches of extremely cold air required for CO$_2$ condensation and cloud formation in the Martian mesosphere. They are created by subgrid-scale gravity waves (GWs) accounted for in the model with the interactively implemented spectral parameterization. Distributions of GW-induced temperature fluctuations and occurrences of supersaturation conditions are in a good agreement with observations of high-altitude CO$_2$ ice clouds. Our study confirms the key role of GWs in facilitating CO$_2$ cloud formation, discusses their tidal modulation, and predicts clouds at altitudes higher than have been observed to date.
We examine the role of small-scale transients in the formation and evolution of solar coronal plumes. We study the dynamics of plume footpoints seen in the vicinity of a coronal hole using the Atmospheric Imaging Assembly (AIA) images, the Helioseismic and Magnetic Imager (HMI) magnetogram on board the Solar Dynamics Observatory (SDO) and spectroscopic data from the Interface Region Imaging Spectrograph (IRIS). Quasi-periodic brightenings are observed in the base of the plumes and are associated with magnetic flux changes. With the high spectral and spatial resolution of IRIS, we identify the sources of these oscillations and try to understand what role the transients at the foot points can play in sustaining the coronal plumes. IRIS sit and stare observation provide a unique opportunity to study the evolution of foot points of the plumes. We notice enhanced line width, intensity and large deviation from the average Doppler shift in the line profiles at specific instances which indicate the presence of flows at the foot points of plumes. We propose that outflows (jet-like features) as a result of small scale reconnections affect the line profiles. These jet-like features may be also responsible for the generation of propagating disturbances within the plumes which are observed to be propagating to larger distances as recorded from multiple AIA channels. These propagating disturbances can be explained in terms of slow magnetoacoustic waves.
Coronal holes are the dark patches in the solar corona associated with relatively cool, less dense plasma and unipolar fields. The fast component of the solar wind emanates from these regions. Several observations reveal the presence of magnetohydrodynamic (MHD) waves in coronal holes which are believed to play a key role in the acceleration of fast solar wind. The recent advent of high-resolution instruments had brought us many new insights on the properties of MHD waves in coronal holes which are reviewed in this article. The advances made in the identification of compressive slow MHD waves in both polar and equatorial coronal holes, their possible connection with the recently discovered high- speed quasi-periodic upflows, their dissipation, and the detection of damping in Alfven waves from the spectral line width variation are discussed in particular.
The small solar-system bodies that reside between 30 and 50 AU are often referred to as the Trans Neptunian Objects, or TNOs. A far-infrared (FIR) mission with survey capabilities, like the prospective Cryogenic Aperture Large Infrared Space Telescope Observatory (CALISTO; Goldsmith et al. 2008), offers the potential for the first time of really probing the population of TNOs, and related populations, down to moderates sizes, and out to distances exceeding 100 AU from the Sun.
A giant planet embedded in a protoplanetary disk forms a gap. An analytic relationship among the gap depth, planet mass $M_{p}$, disk aspect ratio $h_p$, and viscosity $\alpha$ has been found recently, and the gap depth can be written in terms of a single parameter $K= (M_{p}/M_{\ast})^2 h_p^{-5} \alpha^{-1}$. We discuss how observed gap features can be used to constrain the disk and/or planet parameters based on the analytic formula for the gap depth. The constraint on the disk aspect ratio is critical in determining the planet mass so the combination of the observations of the temperature and the image can provide a constraint on the planet mass. We apply the formula for the gap depth to observations of HL~Tau and HD~169142. In the case of HL~Tau, we propose that a planet with $\gtrsim 0.3$ is responsible for the observed gap at $30$~AU from the central star based on the estimate that the gap depth is $\lesssim 1/3$. In the case of HD~169142, the planet mass that causes the gap structure recently found by VLA is $\gtrsim 0.4 M_J$. We also argue that the spiral structure, if observed, can be used to estimate the lower limit of the disk aspect ratio and the planet mass.
Numerical methods to improve the treatment of magnetic fields in smoothed field magnetohydrodynamics (SPMHD) are developed and tested. Chapter 2 is a review of SPMHD. In Chapter 3, a mixed hyperbolic/parabolic scheme is developed which cleans divergence error from the magnetic field. Average divergence error is an order of magnitude lower for all test cases considered, and allows for the stable simulation of the gravitational collapse of magnetised molecular cloud cores. The effectiveness of the cleaning may be improved by explicitly increasing the hyperbolic wave speed or by cycling the cleaning equations between timesteps. In the latter, it is possible to achieve DivB=0. Chapter 4 develops a switch to reduce dissipation of the magnetic field from artificial resistivity. Compared to the existing switch in the literature, this leads to sharper shock profiles in shocktube tests, lower overall dissipation of magnetic energy, and importantly, is able to capture magnetic shocks in the highly super-Alfvenic regime. Chapter 5 compares these numerical methods against grid-based MHD methods (using the Flash code) in simulations of the small-scale dynamo amplification of a magnetic field in driven, isothermal, supersonic turbulence. Both codes exponentially amplify the magnetic energy at a constant rate, though SPMHD shows a resolution dependence that arises from the scaling of the numerical dissipation terms. The time-averaged saturated magnetic spectra have similar shape, and both codes have PDFs of magnetic field strength that are log-normal, which become lopsided as the magnetic field saturates. We conclude that SPMHD is able to reliably simulate the small-scale dynamo amplification of magnetic fields. Chapter 6 concludes the thesis and presents some preliminary work demonstrating that SPMHD can activate the magneto-rotational instability in 2D shearing box tests.
We present a comprehensive re-analysis of stellar photometric variability in the field of the open cluster M37 following the application of a new photometry and de-trending method to MMT/Megacam image archive. This new analysis allows a rare opportunity to explore photometric variability over a broad range of time-scales, from minutes to a month. The intent of this work is to examine the entire sample of over 30,000 objects for periodic, aperiodic, and sporadic behaviors in their light curves. We show a modified version of the fast $\chi^{2}$ periodogram algorithm (F$\chi^{2}$) and change-point analysis (CPA) as tools for detecting and assessing the significance of periodic and non-periodic variations. The benefits of our new photometry and analysis methods are evident. A total of 2306 stars exhibit convincing variations that are induced by flares, pulsations, eclipses, starspots, and unknown causes in some cases. This represents a 60% increase in the number of variables known in this field. Moreover, 30 of the previously identified variables are found to be false positives resulting from time-dependent systematic effects. New catalog includes 61 eclipsing binary systems, 92 multiperiodic variable stars, 132 aperiodic variables, and 436 flare stars, as well as several hundreds of rotating variables. Based on extended and improved catalog of variables, we investigate the basic properties (e.g., period, amplitude, type) of all variables. The catalog can be accessed through the web interface (this http URL).
The Magellanic clouds are uniquely placed to study the stellar contribution to dust emission. Individual stars can be resolved in these systems even in the mid-infrared, and they are close enough to allow detection of infrared excess caused by dust.We have searched the Spitzer Space Telescope data archive for all Infrared Spectrograph (IRS) staring-mode observations of the Small Magellanic Cloud (SMC) and found that 209 Infrared Array Camera (IRAC) point sources within the footprint of the Surveying the Agents of Galaxy Evolution in the Small Magellanic Cloud (SAGE-SMC) Spitzer Legacy programme were targeted, within a total of 311 staring mode observations. We classify these point sources using a decision tree method of object classification, based on infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information. We find 58 asymptotic giant branch (AGB) stars, 51 young stellar objects (YSOs), 4 post-AGB objects, 22 Red Supergiants (RSGs), 27 stars (of which 23 are dusty OB stars), 24 planetary nebulae (PNe), 10Wolf-Rayet (WR) stars, 3 Hii regions, 3 R Coronae Borealis (R CrB) stars, 1 Blue Supergiant and 6 other objects, including 2 foreground AGB stars. We use these classifications to evaluate the success of photometric classification methods reported in the literature.
We use self-consistent N-body simulations to study the interaction of massive classical bulges (ClBs) with a bar that forms self-consistently in the disc. We show that the ClB gains significant angular momentum from the bar which, surprisingly, scales approximately linearly with the ClB mass. It is also tightly correlated with the ratio of the bulge size to the bar size. Most of the angular momentum gain occurs via low-order resonances, particularly 5:2 resonant orbits. A density wake forms in the ClB which corotates and aligns with the bar at the end of the evolution. The spin-up process creates a characteristic linear rotation profile and mild tangential anisotropy in the ClB. The induced rotation is small in the centre but significant beyond ~bulge half mass radii, where it leads to mass-weighted V/\sigma ~ 0.2, and reaches a local V/\sigma_in ~ 0.5 at around the scale of the bar. In all models a box/peanut bulge also forms suggesting that composite bulges may be common.
For most hierarchical triple stars, the classical double two-body model of zeroth-order cannot describe the motions of the components under the current observational accuracy. In this paper, Marchal's first-order analytical solution is implemented and a more efficient simplified version is applied to real triple stars. The results show that, for most triple stars, the proposed first-order model is preferable to the zeroth-order model either in fitting observational data or in predicting component positions.
Interstellar dust in galaxies can be traced either through its extinction effects on the star light, or through its thermal emission at infrared wavelengths. Recent radiative transfer studies of several nearby edge-on galaxies have found an apparent inconsistency in the dust energy balance: the radiative transfer models that successfully explain the optical extinction underestimate the observed fluxes by an average factor of three. We investigate the dust energy balance for IC4225 and NGC5166, two edge-on spiral galaxies observed by the Herschel Space Observatory in the frame of the H-ATLAS survey. We start from models which were constrained from optical data and extend them to construct the entire spectral energy distribution of our galaxies. These predicted values are subsequently compared to the observed far-infrared fluxes. We find that including a young stellar population in the modelling is necessary as it plays a non-negligible part in the heating of the dust grains. While the modelling approach for both galaxies is nearly identical, we find two very different results. As is often seen in other edge-on spiral galaxies, the far-infrared emission of our radiative transfer model of IC4225 underestimates the observed fluxes by a factor of about three. For NGC5166 on the other hand, we find that both the predicted spectral energy distribution as well as the simulated images match the observations particularly well. We explore possible reasons for this difference and conclude that it is unlikely that one single mechanism is the cause of the dust energy balance problem in spiral galaxies. We discuss the different approaches that can be considered in order to get a conclusive answer on the origin this discrepancy.
(abridged for arXiv) The BEER algorithm, introduced by Faigler & Mazeh (2011), searches stellar lightcurves for the BEaming, Ellipsoidal, and Reflection photometric modulations caused by a short-period companion. Applying the search to the first five long-run center CoRoT fields, we identified $481$ non-eclipsing candidates with periodic flux amplitudes of $0.5-87$ mmag. Optimizing the Anglo-Australian-Telescope pointing coordinates and the AAOmega fiber-allocations with dedicated softwares, we acquired $6-7$ medium-resolution spectra of $281$ candidates in a seven-night campaign. Analysis of the red-arm AAOmega spectra, which covered the range of $8342-8842$ \AA{}, yielded a radial-velocity precision of $\sim1$ km/s. Spectra containing lines of more than one star were analyzed with TODCOR$-$the two-dimensional correlation algorithm. The measured radial velocities confirmed the binarity of seventy of the BEER candidates$-45$ single-line binaries, $18$ double-line binaries, and $7$ diluted binaries. We show that red giants introduce a major source of false candidates, and demonstrate a way to improve BEER's performance in extracting higher-fidelity samples from future searches of CoRoT lightcurves. The periods of the confirmed binaries span a range of $0.3-10$ days, and show a rise in the number of binaries per $\Delta$log$P$ towards longer periods. The estimated mass ratios of the double-line binaries and the mass-ratios assigned to the single-line binaries, assuming an isotropic inclination distribution, span a range of $0.03-1$. On the low-mass end we have detected two brown-dwarf candidates on a $\sim1$ day period orbit. This is the first time non-eclipsing beaming binaries are detected in CoRoT data, and we estimate that $\sim300$ such binaries can be detected in the CoRoT long-run lightcurves.
The question of possible small-scale dynamo action in the surface layers of the Sun is revisited with realistic 3D MHD simulations. As in other MHD problems, dynamo action is found to be a sensitive function of the magnetic Prandtl number ${\rm P_{\rm m} }=\nu/\eta$; it disappears below a critical value ${\rm P_{\rm c}}$ which is a function of the numerical resolution. At a grid spacing of 3.5 km, ${\rm P_{\rm c}}$ based on the hyperdiffusivities implemented in the code (STAGGER) is $\approx 1$, increasing with increasing grid spacing. As in other settings, it remains uncertain whether small scale dynamo action is present in the astrophysical limit where ${\rm P_{\rm m} }<<1$ and magnetic Reynolds number ${\rm R_m}\gg 1$. The question is discussed in the context of the strong effect that external stray fields are observed to have in generating and maintaining dynamo action in other numerical and laboratory systems, and in connection with the type-II hypertransient behavior of dynamo action observed in the absence of such external fields.
Recent observations of brown dwarf spectroscopic variability in the infrared infer the presence of patchy cloud cover. This paper proposes a mechanism for producing inhomogeneous cloud coverage due to the depletion of cloud particles through the Coulomb explosion of dust in atmospheric plasma regions. Charged dust grains Coulomb-explode when the electrostatic stress of the grain exceeds its mechanical tensile stress, which results in grains below a critical radius $a<a^{\rm Coul}_{\rm crit}$ being broken up. This work outlines the criteria required for the Coulomb explosion of dust clouds in substellar atmospheres, the effect on the dust particle size distribution function, and the resulting radiative properties of the atmospheric regions. Our results show that for an atmospheric plasma region with an electron temperature of $T_{e}=10$~eV ($\approx10^{5}$~K), the critical grain radius varies from $10^{-7}$ to $10^{-4}$~cm, depending on the grains' tensile strength. Higher critical radii up to $10^{-3}$~cm are attainable for higher electron temperatures. We find that the process produces a bimodal particle size distribution composed of stable nanoscale seed particles and dust particles with $a\geq a^{\rm Coul}_{\rm crit}$, with the intervening particle sizes defining a region devoid of dust. As a result, the dust population is depleted, and the clouds become optically thin in the wavelength range $0.1-10~\mu$m, with a characteristic peak that shifts to higher wavelengths as more sub-micrometer particles are destroyed. In an atmosphere populated with a distribution of plasma volumes, this will yield regions of contrasting radiative properties, thereby giving a source of inhomogeneous cloud coverage. The results presented here may also be relevant for dust in supernova remnants and protoplanetary disks.
Deep HI observations of the outer parts of disc galaxies demonstrate the frequent presence of extended, well-developed spiral arms far beyond the optical radius. To understand the nature and the origin of such outer spiral structure, we investigate the propagation in the outer gaseous disc of large-scale spiral waves excited in the bright optical disc. Using hydrodynamical simulations, we show that non-axisymmetric density waves, penetrating in the gas through the outer Lindblad resonance, can exhibit relatively regular spiral structures outside the bright optical stellar disc. For low-amplitude structures, the results of numerical simulations match the predictions of a simple WKB linear theory. The amplitude of spiral structure increases rapidly with radius. Beyond $\approx 2$ optical radii, spirals become nonlinear (the linear theory becomes quantitatively and qualitatively inadequate) and unstable to Kelvin-Helmholtz instability. In numerical simulations, in models for which gas is available very far out, spiral arms can extend out to 25 disc scale-lengths. A comparison between the properties of the models we have investigated and the observed properties of individual galaxies may shed light into the problem of the amount and distribution of dark matter in the outer halo.
We present a comparison of 14 galaxy formation models: 12 different semi-analytical models and 2 halo-occupation distribution models for galaxy formation based upon the same cosmological simulation and merger tree information derived from it. The participating codes have proven to be very successful in their own right but they have all been calibrated independently using various observational data sets, stellar models, and merger trees. In this paper we apply them without recalibration and this leads to a wide variety of predictions for the stellar mass function, specific star formation rates, stellar-to- halo mass ratios, and the abundance of orphan galaxies. The scatter is much larger than seen in previous comparison studies primarily because the codes have been used outside of their native environment within which they are well tested and calibrated. The purpose of the `nIFTy comparison of galaxy formation models' is to bring together as many different galaxy formation modellers as possible and to investigate a common approach to model calibration. This paper provides a unified description for all participating models and presents the initial, uncalibrated comparison as a baseline for our future studies where we will develop a common calibration framework and address the extent to which that reduces the scatter in the model predictions seen here.
The Orion cloud complex presents a variety of star formation mechanisms and properties and it is still one of the most intriguing targets for star formation studies. We present VISTA/VIRCAM near-infrared observations of the L1630N star forming region, including the stellar clusters NGC 2068 and NGC 2071, in the Orion molecular cloud B and discuss them in combination with Spitzer data. We select 186 young stellar object (YSO) candidates in the region on the basis of multi-colour criteria, confirm the YSO nature of the majority of them using published spectroscopy from the literature, and use this sample to investigate the overall star formation properties in L1630N. The K-band luminosity function of L1630N is remarkably similar to that of the Trapezium cluster, i.e., it presents a broad peak in the range 0.3-0.7 M$_\odot$ and a fraction of sub-stellar objects of $\sim$20%. The fraction of YSOs still surrounded by disk/envelopes is very high ($\sim$85%) compared to other star forming regions of similar age (1-2 Myr), but includes some uncertain corrections for diskless YSOs. Yet, a possibly high disk fraction together with the fact that 1/3 of the cloud mass has a gas surface density above the threshold for star formation ($\sim$129 M$_\odot$ pc$^{-2}$), points towards a still on-going star formation activity in L1630N. The star formation efficiency (SFE), star formation rate (SFR) and density of star formation of L1630N are within the ranges estimated for galactic star forming regions by the Spitzer "core to disk" and "Gould's Belt" surveys. However, the SFE and SFR are lower than the average value measured in the Orion A cloud and, in particular, lower than that in the southern regions of L1630. This might suggest different star formation mechanisms within the L1630 cloud complex.
This article discusses various methods of representing and manipulating arbitrary coverage information in two dimensions, with a focus on space- and time-efficiency when working with these coverages, storing them on disk and transmitting them between computers. While these considerations were originally motivated by the specific task of representing sky coverage and catalogue cross-matching for astronomical surveys, they can be profitably applied in many other situations as well.
According to the recycling scenario, millisecond pulsars (MSPs) have evolved from low-mass X-ray binaries (LMXBs). Their orbits are expected to be circular due to tidal interactions during the binary evolution, as observed in most of the binary MSPs. There are some peculiar systems that do not fit this picture. Three recent examples are PSRs J2234$+$06, J1946$+$3417 and J1950$+$2414, all of which are MSPs in eccentric orbits but with mass functions compatible with expected He white dwarf companions. It has been suggested these MSPs may have formed from delayed accretion-induced collapse of massive white dwarfs, or the eccentricity may be induced by dynamical interaction between the binary and a circumbinary disk. Assuming that the core density of accreting neutron stars in LMXBs may reach the density of quark deconfinement, which can lead to phase transition from neutron stars to strange quark stars, we show that the resultant MSPs are likely to have an eccentric orbit, due to the sudden loss of the gravitational mass of the neutron star during the transition. The eccentricities can be reproduced with a reasonable estimate of the mass loss. This scenario might also account for the formation of the youngest known X-ray binary Cir X$-$1, which also possesses a low-field compact star in an eccentric orbit.
Classical Sweet-Parker models of reconnection predict that reconnection rates depend inversely on the resistivity, usually parameterized using the dimensionless Lundquist number ($\Lund$). We describe magnetohydrodynamic (MHD) simulations using a static, nested grid that show the development of a three-dimensional instability in the plane of a current sheet between reversing field lines without a guide field. The instability leads to rapid reconnection of magnetic field lines at a rate independent of $\Lund$ over at least the range $3.2\times 10^3 \lesssim \Lund \lesssim 3.2 \times 10^5$ resolved by the simulations. We find that this instability occurs even for cases with $\Lund \lesssim 10^4$ that in our models appear stable to the recently described, two-dimensional, plasmoid instability. Our results suggest that three-dimensional, MHD processes alone produce fast (resistivity independent) reconnection without recourse to kinetic effects or external turbulence. The unstable reconnection layers provide a self-consistent environment in which the extensively studied turbulent reconnection process can occur.
We study the simple gauge invariant model ${f^2}FF$ as a way to generate primordial magnetic fields (PMF) in Natural Inflation (NI). We compute both magnetic and electric spectra generated by the ${f^2}FF$ model in NI for different values of model parameters and find that both de Sitter and power law expansion lead to the same results at sufficiently large number of e-foldings. We also find that the necessary scale invariance property of the PMF cannot be obtained in NI in first order of slow roll limits under the constraint of inflationary potential, $V\left( 0 \right) \simeq 0$. Furthermore, if this constraint is relaxed to achieve scale invariance, then the model suffers from the backreaction problem for almost all values of model parameters. We show that there is a narrow range of the height of the potential $\Lambda $ around ${\Lambda _{\min }} \approx 0.00874{M_{{\rm{Pl}}}}$ and of the co-moving wave number $k$ around ${k_{\min }} \sim 0.0173{\rm{Mp}}{{\rm{c}}^{ - 1}}$, at which the problem of backreaction might be avoided. The value of ${\Lambda _{\min }}$ lies within the range of $\Lambda $ compatible with the BICEP2 results, and the range of $k$ lies within some the observable scale. However, the relatively short range of $k$ presents a serious challenge to the viability of this model.
It has recently been shown that the presence of a spectator pseudoscalar field, coupled to photons through a Chern-Simons term, can amplify the primordial tensor spectrum without observationally disrupting the primordial scalar spectrum. The amplification occurs due to an instability that develops for the vector fields. We extend previous studies to account for the contribution arising from an inhomogeneous vector background, which emerges as the dominant correction to the primordial tensor spectrum. These semiclassical contributions dominate over the quantum loop contributions and possibly enhance the primordial tensor spectrum such as to have observational effects even though the loop corrections might be undetectable. A similar effect would occur by replacing the visible electromagnetic U(1) by an unbroken dark U(1).
We describe an overall picture of galactic-scale star formation. Recent high-resolution magneto-hydrodynamical simulations of two-fluid dynamics with cooling/heating and thermal conduction have shown that the formation of molecular clouds requires multiple episodes of supersonic compression. This finding enables us to create a scenario in which molecular clouds form in interacting shells or bubbles on a galactic scale. First we estimate the ensemble-averaged growth rate of molecular clouds over a timescale larger than a million years. Next we perform radiation hydrodynamics simulations to evaluate the destruction rate of magnetized molecular clouds by the stellar FUV radiation. We also investigate the resultant star formation efficiency within a cloud which amounts to a low value (a few percent) if we adopt the power-law exponent -2.5 for the mass distribution of stars in the cloud. We finally describe the time evolution of the mass function of molecular clouds over a long timescale (>1Myr) and discuss the steady state exponent of the power-law slope in various environments.
Galaxy evolution scenarios predict that the feedback of star formation and nuclear activity (AGN) can drive the transformation of gas-rich spiral mergers into ULIRGs, and, eventually, lead to the build-up of QSO/elliptical hosts. We study the role that star formation and AGN feedback have in launching and maintaining the molecular outflows in two starburst-dominated advanced mergers, NGC1614 and IRAS17208-0014, by analyzing the distribution and kinematics of their molecular gas reservoirs. We have used the PdBI array to image with high spatial resolution (0.5"-1.2") the CO(1-0) and CO(2-1) line emissions in NGC1614 and IRAS17208-0014, respectively. The velocity fields of the gas are analyzed and modeled to find the evidence of molecular outflows in these sources and characterize the mass, momentum and energy of these components. While most (>95%) of the CO emission stems from spatially-resolved (~2-3kpc-diameter) rotating disks, we also detect in both mergers the emission from high-velocity line wings that extend up to +-500-700km/s, well beyond the estimated virial range associated with rotation and turbulence. The kinematic major axis of the line wing emission is tilted by ~90deg in NGC1614 and by ~180deg in IRAS17208-0014 relative to their respective rotating disk major axes. These results can be explained by the existence of non-coplanar molecular outflows in both systems. In stark contrast with NGC1614, where star formation alone can drive its molecular outflow, the mass, energy and momentum budget requirements of the molecular outflow in IRAS17208-0014 can be best accounted for by the existence of a so far undetected (hidden) AGN of L_AGN~7x10^11 L_sun. The geometry of the molecular outflow in IRAS17208-0014 suggests that the outflow is launched by a non-coplanar disk that may be associated with a buried AGN in the western nucleus.
We present the target selection process for the Multi-object APO Radial Velocity Exoplanets Large-area Survey (MARVELS), which is part of the Sloan Digital Sky Survey (SDSS) III. MARVELS is a medium-resolution ($R \sim 11000$) multi-fiber spectrograph capable of obtaining radial velocities for 60 objects at a time in order to find brown dwarfs and giant planets. The survey was configured to target dwarf stars with effective temperatures approximately between $4500$ and $6250 \, \mbox{K}$. For the first 2 years MARVELS relied on low-resolution spectroscopic pre-observations to estimate the effective temperature and $\log(g)$ for candidate stars and then selected suitable dwarf stars from this pool. Ultimately, the pre-observation spectra proved ineffective at filtering out giant stars; many giants were incorrectly classified as dwarfs, resulting in a giant contamination rate of $\sim$30\% for the first phase of the MARVELS survey. Thereafter, the survey instead applied a reduced proper motion cut to eliminate giants and used the Infrared Flux Method to estimate effective temperatures, using only extant photometric and proper-motion catalog information. The target selection method introduced here may be useful for other surveys that need to rely on extant catalog data for selection of specific stellar populations.
Propagating disturbances are often observed in active region fan-like coronal loops. They were thought to be due to slow mode MHD waves based on some of the observed properties. But the recent studies involving spectroscopy indicate that they could be due to high speed quasi-periodic upflows which are difficult to distinguish from upward propagating slow waves. In this context, we have studied a fan loop structure in the active region AR 11465 using simultaneous spectroscopic and imaging observations from Extreme-ultraviolet Imaging Spectrometer (EIS) on board Hinode and Atmospheric Imaging Assembly (AIA) on board SDO. Analysis of the data shows significant oscillations at different locations. We explore the variations in different line parameters to determine whether the waves or flows could cause these oscillations to improve the current understanding on the nature of these disturbances.
The past decade has seen the rise of various radio astronomy arrays, particularly for low-frequency observations below 100MHz. These developments have been primarily driven by interesting and fundamental scientific questions, such as studying the dark ages and epoch of re-ionization, by detecting the highly red-shifted 21cm line emission. However, Earth-based radio astronomy below frequencies of 30MHz is severely restricted due to man-made interference, ionospheric distortion and almost complete non-transparency of the ionosphere below 10MHz. Therefore, this narrow spectral band remains possibly the last unexplored frequency range in radio astronomy. A straightforward solution to study the universe at these frequencies is to deploy a space-based antenna array far away from Earths' ionosphere. Various studies in the past were principally limited by technology and computing resources, however current processing and communication trends indicate otherwise. We briefly present the achievable science cases, and discuss the system design for selected scenarios, such as extra-galactic surveys. An extensive discussion is presented on various sub-systems of the potential satellite array, such as radio astronomical antenna design, the on-board signal processing, communication architectures and joint space-time estimation of the satellite network. In light of a scalable array and to avert single point of failure, we propose both centralized and distributed solutions for the ULW space-based array. We highlight the benefits of various deployment locations and summarize the technological challenges for future space-based radio arrays.
Context. Some circumstellar-interacting (CSI) supernovae (SNe) are produced by the explosions of massive stars that have lost mass shortly before the SN explosion. There is evidence that the precursors of some SNe IIn were luminous blue variable (LBV) stars. For a small number of CSI SNe, outbursts have been observed before the SN explosion. Eruptive events of massive stars are named as SN impostors (SN IMs) and whether they herald a forthcoming SN or not is still unclear. The large variety of observational properties of CSI SNe suggests the existence of other progenitors, such as red supergiant (RSG) stars with superwinds. Furthermore, the role of metallicity in the mass loss of CSI SN progenitors is still largely unexplored. Aims. Our goal is to gain insight on the nature of the progenitor stars of CSI SNe by studying their environments, in particular the metallicity at their locations. Methods. We obtain metallicity measurements at the location of 60 transients (including SNe IIn, SNe Ibn, and SN IMs), via emission-line diagnostic on optical spectra obtained at the Nordic Optical Telescope and through public archives. Metallicity values from the literature complement our sample. We compare the metallicity distributions among the different CSI SN subtypes and to those of other core-collapse SN types. We also search for possible correlations between metallicity and CSI SN observational properties. Results. We find that SN IMs tend to occur in environments with lower metallicity than those of SNe IIn. Among SNe IIn, SN IIn-L(1998S-like) SNe show higher metallicities, similar to those of SNe IIL/P, whereas long-lasting SNe IIn (1988Z-like) show lower metallicities, similar to those of SN IMs. The metallicity distribution of SNe IIn can be reproduced by combining the metallicity distributions of SN IMs (that may be produced by major outbursts of massive stars like LBVs) and SNe IIP (produced by RSGs). The same applies to the distributions of the Normalized Cumulative Rank (NCR) values, which quantifies the SN association to H II regions. For SNe IIn, we find larger mass-loss rates and higher CSM velocities at higher metallicities. The luminosity increment in the optical bands during SN IM outbursts tend to be larger at higher metallicity, whereas the SN IM quiescent optical luminosities tend to be lower. Conclusions. The difference in metallicity between SNe IIn and SN IMs suggests that LBVs are only one of the progenitor channels for SNe IIn, with 1988Z-like and 1998S-like SNe possibly arising from LBVs and RSGs, respectively. Finally, even though linedriven winds likely do not primarily drive the late mass-loss of CSI SN progenitors, metallicity has some impact on the observational properties of these transients. Key words. supernovae: general - stars: evolution - galaxies: abundances
The convective envelopes of cool main-sequence stars harbour magnetic fields with a complex global and local structure. These fields affect the near-surface convection and the outer stellar atmospheres in many ways and are responsible for the observable magnetic activity of stars. Our aim is to understand the local structure in unipolar regions with moderate average magnetic flux density. These correspond to plage regions covering a substantial fraction of the surface of the Sun (and likely also the surface of other Sun-like stars) during periods of high magnetic activity. We analyse the results of 18 local-box magnetohydrodynamics simulations covering the upper layers of the convection zones and the photospheres of cool main-sequence stars of spectral types F to early M. The average vertical field in these simulations ranges from 20 to 500G. We find a substantial variation of the properties of the surface magnetoconvection between main-sequence stars of different spectral types. As a consequence of a reduced efficiency of the convective collapse of flux tubes, M dwarfs lack bright magnetic structures in unipolar regions of moderate field strength. The spatial correlation between velocity and the magnetic field as well as the lifetime of magnetic structures and their sizes relative to the granules vary significantly along the model sequence of stellar types.
We present an updated version of the {\it SimProp} Monte Carlo code to study the propagation of ultra high energy cosmic rays in astrophysical backgrounds computing the cosmogenic neutrino fluxes expected on earth. The study of secondary neutrinos provides a powerful tool to constrain the source models of these extremely energetic particles. We will show how the newly detected IceCube neutrino events at PeV energies together with the the latest experimental results of the Pierre Auger Observatory and Telescope Array experiment are almost at the level of excluding several hypothesis on the astrophysical sources of ultra high energy cosmic rays. Results presented here can be also used to evaluate the discovery capabilities of future high energy cosmic rays and neutrino detectors.
Magnetic fields affect the local structure of the photosphere of stars. They can considerably influence the radiative properties near the optical surface, flow velocities, and the temperature and pressure profiles. We aim at understanding qualitatively the influence of small magnetic flux concentrations in unipolar plage regions on the centre-to-limb variation of the intensity and its contrast and on the shape of spectral line profiles in cool main-sequence stars. We analyse the bolometric and continuum intensity and its angular dependence of 24 radiative magnetohydrodynamic simulations of the near-surface layers of main-sequence stars with six different sets of stellar parameters (spectral types F to early M) and four different average magnetic field strengths (including the non-magnetic case). We also calculated disc-integrated profiles of three spectral lines. The small magnetic flux concentrations formed in the magnetic runs of simulations have a considerable impact on the intensity and its centre-to-limb variation. Spectral lines are not only broadened owing to the Zeeman effect, but are also strongly affected by the modified thermodynamical structure and flow patterns. This indirect magnetic impact on the line profiles is often bigger than that of the Zeeman effect. The effects of the magnetic field on the radiation leaving the star can be considerable and is not restricted to spectral line broadening and polarisation by the Zeeman effect. The inhomogeneous structure of the magnetic field on small length scales and its impact on (and spatial correlation with) the local thermodynamical structure and the flow field near the surface influence the measurement of the global field properties and stellar parameters. These effects need to be taken into account in the interpretation of observations.
Previous work on possible surface reflectance biosignatures for Earth-like planets has typically focused on analogues to spectral features produced by photosynthetic organisms on Earth, such as the vegetation red edge. Although oxygenic photosynthesis, facilitated by pigments evolved to capture photons, is the dominant metabolism on our planet, pigmentation has evolved for multiple purposes to adapt organisms to their environment. We present an interdisciplinary study of the diversity and detectability of nonphotosynthetic pigments as biosignatures, which includes a description of environments that host nonphotosynthetic biologically pigmented surfaces, and a lab-based experimental analysis of the spectral and broadband color diversity of pigmented organisms on Earth. We test the utility of broadband color to distinguish between Earth-like planets with significant coverage of nonphotosynthetic pigments and those with photosynthetic or nonbiological surfaces, using both 1-D and 3-D spectral models. We demonstrate that, given sufficient surface coverage, nonphotosynthetic pigments could significantly impact the disk-averaged spectrum of a planet. However, we find that due to the possible diversity of organisms and environments, and the confounding effects of the atmosphere and clouds, determination of substantial coverage by biologically produced pigments would be difficult with broadband colors alone and would likely require spectrally resolved data.
The initial conditions for $N$-body simulations are usually generated by applying the Zel'dovich approximation to the initial displacements of the particles using an initial power spectrum of density fluctuations generated by an Einstein-Boltzmann solver. We show that the initial displacements generated in this way generally receive a first-order relativistic correction. We define a new gauge, the $N$-body gauge, in which this relativistic correction is absent and show that a conventional Newtonian $N$-body simulation includes all first-order relativistic contributions if we identify the coordinates in Newtonian simulations with those in the $N$-body gauge.
Observations suggest that high-redshift galaxies are either very dusty or essentially dust free. The evolution from one regime to the other must also be very fast, since evolved and dusty galaxies show up at redshifts corresponding to a Universe which is only about 500 Myr old. In the present paper models which predicts the existence of an apparent dichotomy between dusty and dust-free galaxies at high redshift are considered. Galaxies become dusty as soon as they reach an evolved state and the transition is very rapid. A special case suggests that while stellar dust production is overall relatively insignificant -- contrary to what has been argued recently -- it can at the same time be consistent with efficient dust production in supernovae in the local Universe. Special attention will be given to the recent discovery of a dusty normal galaxy (A1689-zD1) at a very high redshift z = 7.5 +/- 0.2.
The fitting of radial velocity curves is a frequent procedure in binary stars and exoplanet research. In the majority of cases the fitting routines need to be fed with a set of initial parameter values and priors from which to begin the computations and their results can be affected by local minima. We present a new code, the rvfit code, for fitting radial velocities of stellar binaries and exoplanets using an Adaptive Simulated Annealing (ASA) global minimization method, which fastly converges to a global solution minimum without the need to provide preliminary parameter values. We show the performance of the code using both synthetic and real data sets: double-lined binaries, single-lined binaries, and exoplanet systems. In all examples the keplerian orbital parameters fitted by the rvfit code and their computed uncertainties are compared with literature solutions. Finally, we provide the source code with a working example and a detailed description on how to use it.
We estimate the effective area available for cosmic-ray detection with a network of smartphones under optimistic conditions. To measure cosmic-ray air showers with a minimally-adequate precision and a detection area similar to existing ground-based detectors, the fraction of participating users needs to unrealistically large. We conclude that the prospects of cosmic-ray research using smartphones are very limited.
Kerr black holes have their angular momentum, $J$, bounded by their mass, $M$: $Jc\leqslant GM^2$. There are, however, known black hole solutions violating this Kerr bound. We propose a very simple universal bound on the rotation, rather than on the angular momentum, of four-dimensional, stationary and axisymmetric, asymptotically flat black holes, given in terms of an appropriately defined horizon linear velocity, $v_H$. The $v_H$ bound is simply that $v_H$ cannot exceed the velocity of light. We verify the $v_H$ bound for known black hole solutions, including some that violate the Kerr bound, and conjecture that only extremal Kerr black holes saturate the $v_H$ bound.
We consider theories where dark matter is composed of a thermal relic of weak scale mass, whose couplings to the Standard Model (SM) are however too small to give rise to the observed abundance. Instead, the abundance is set by annihilation to light hidden sector states that carry no charges under the SM gauge interactions. In such a scenario the constraints from direct and indirect detection, and from collider searches for dark matter, can easily be satisfied. The masses of such light hidden states can be protected by symmetry if they are Nambu-Goldstone bosons, fermions, or gauge bosons. These states can then contribute to the cosmic energy density as dark radiation, leading to observable signals in the cosmic microwave background (CMB). Furthermore, depending on whether or not the light hidden sector states self-interact, the fraction of the total energy density that free-streams is either decreased or increased, leading to characteristic effects on both the scalar and tensor components of the CMB anisotropy that allows these two cases to be distinguished. The magnitude of these signals depends on the number of light degrees of freedom in the hidden sector, and on the temperature at which it kinetically decouples from the SM. We consider a simple model that realizes this scenario, based on a framework in which the SM and hidden sector are initially in thermal equilibrium through the Higgs portal, and show that the resulting signals are compatible with recent Planck results, while large enough to be detected in upcoming experiments such as CMBPol and CMB Stage-IV. Invisible decays of the Higgs into hidden sector states at colliders can offer a complementary probe of this model.
The paper contains description of the main properties of the galactic dark matter (DM) particles, available approaches for detection of DM, main features of direct DM detection, ways to estimate prospects for the DM detection, the first collider search for a DM candidate within an Effective Field Theory, complete review of ATLAS results of the DM candidate search with LHC RUN I, and less complete review of "exotic" dark particle searches with other accelerators and not only. From these considerations it follows that one is unable to prove, especially model-independently,a discovery of a DM particle with an accelerator, or collider. One can only obtain evidence on existence of a weakly interacting neutral particle, which could be, or could not be the DM candidate. The current LHC DM search program uses only the missing transverse energy signature. Non-observation of any excess above Standard Model expectations forces the LHC experiments to enter into the same fighting for the best exclusion curve, in which (almost) all direct and indirect DM search experiments permanently take place. But this fighting has very little (almost nothing) to do with a real possibility of discovering a DM particle. The true DM particles possess an exclusive galactic signature --- annual modulation of a signal, which is accessible today only for direct DM detection experiments. There is no way for it with a collider, or accelerator. Therefore to prove the DM nature of a collider-discovered candidate one must find the candidate in a direct DM experiment and demonstrate the galactic signature for the candidate. Furthermore, being observed, the DM particle must be implemented into a modern theoretical framework. The best candidate is the supersymmetry, which looks today inevitable for coherent interpretation of all available DM data.
We describe the primeval inflationary phase of the early Universe within a quantum field theoretical (QFT) framework that can be viewed as the effective action of vacuum decay in the early times. Interestingly enough, the model accounts for the "graceful exit" of the inflationary phase into the standard radiation regime. The underlying QFT framework considered here is Supergravity (SUGRA), more specifically an existing formulation in which the Starobinsky-type inflation (de-Sitter background) emerges from the quantum corrections to the effective action after integrating out the gravitino fields in their (dynamically induced) massive phase. We also demonstrate that the structure of the effective action in this model is consistent with the generic idea of renormalization group (RG) running of the cosmological parameters, specifically it follows from the corresponding RG equation for the vacuum energy density as a function of the Hubble rate, $\rho_{\Lambda}(H)$. Overall our combined approach amounts to a concrete-model realization of inflation triggered by vacuum decay in a fundamental physics context which, as it turns out, can also be extended for the remaining epochs of the cosmological evolution until the current dark energy era.
The transit of primordial black holes through a white dwarf causes localized heating around the trajectory of the black hole through dynamical friction. For sufficiently massive black holes, this heat can initiate runaway thermonuclear fusion causing the white dwarf to explode as a supernova. The shape of the observed distribution of white dwarfs with masses up to $1.25 M_{\odot}$ rules out primordial black holes with masses $\sim 10^{19}$ gm - $10^{20}$ gm as a dominant constituent of the local dark matter density. Black holes with masses as large as $10^{24}$ gm will be excluded if recent observations by the NuStar collaboration of a population of white dwarfs near the galactic center are confirmed. Black holes in the mass range $10^{20}$ gm - $10^{22}$ gm are also constrained by the observed supernova rate, though these bounds are subject to astrophysical uncertainties. These bounds can be further strengthened through measurements of white dwarf binaries in gravitational wave observatories. The mechanism proposed in this paper can constrain a variety of other dark matter scenarios such as Q balls, annihilation/collision of large composite states of dark matter and models of dark matter where the accretion of dark matter leads to the formation of compact cores within the star. White dwarfs, with their astronomical lifetimes and sizes, can thus act as large space-time volume detectors enabling a unique probe of the properties of dark matter, especially of dark matter candidates that have low number density. This mechanism also raises the intriguing possibility that a class of supernova may be triggered through rare events induced by dark matter rather than the conventional mechanism of accreting white dwarfs that explode upon reaching the Chandrasekhar mass.
We show that General Relativity coupled to a quantum field theory generically leads to non-local effects in the matter sector. These non-local effects can be described by non-local higher dimensional operators which remarkably have an approximate shift symmetry. When applied to inflationary models, our results imply that small non-Gaussianities are a generic feature of models based on General Relativity coupled to matter fields. However, these effects are too small to be observable in the Cosmic Microwave Background.
Continuing work initiated in earlier publications [Ichita, Yamada and Asada, Phys. Rev. D {\bf 83}, 084026 (2011); Yamada and Asada, Phys. Rev. D {\bf 86}, 124029 (2012)], we examine the post-Newtonian (PN) effects on the stability of the triangular solution in the relativistic three-body problem for general masses. For three finite masses, a condition for stability of the triangular solution is obtained at the first post-Newtonian (1PN) order, and it recovers previous results for the PN restricted three-body problem when one mass goes to zero. The stability regions still exist even at the 1PN order, though the PN triangular configuration for general masses is less stable than the PN restricted three-body case as well as the Newtonian one.
The magnetohydrodynamic linear stability with the localized bulk flow oriented parallel to the neutral sheet is investigated, by including the Hall effect and the guide magnetic field. We observe three different unstable modes: a "streaming tearing" mode at a slow flow speed, a "streaming sausage" mode at a medium flow speed, and a "streaming kink" mode at a fast flow speed. The streaming tearing and sausage modes have a standard tearing mode-like structure with symmetric density fluctuations in the neutral sheet, while the kink mode has an asymmetric fluctuation. The growth rate of the streaming tearing mode decreases with increasing magnetic Reynolds number, while the growth rates of the sausage and kink modes do not depend strongly on the Reynolds number. The sausage and kink modes can be unstable for not only super-Alfv\'enic flow but also sub-Alfv\'enic flow when the lobe density is low. The wavelengths of these unstable modes are of the same order of magnitude as the thickness of the plasma sheet. Their maximum growth rates are higher than that of a standard tearing mode, and under a strong guide magnetic field, the growth rates of the sausage and kink modes are enhanced, while under a weak guide magnetic field, they are suppressed. For a thin plasma sheet with the Hall effect, the fluctuations of the streaming modes can exist over the plasma sheet. These unstable modes may be regarded as being one of the processes generating Alfv\'enic turbulence in the plasma sheet during magnetic reconnection.
The recently observed excess in gamma-ray signal near the Galactic center suggests that dark matter particles may annihilate into charged fermions that produce gamma-ray to be observed. In this paper, we consider a leptonic dark matter, which annihilates into the standard model leptons, $\mu^+ \mu^-$ and $\tau^+ \tau^-$, by the interaction of the gauged lepton number ${\rm U(1)}_{L_\mu-L_\tau}$ and fits the observed excess. Interestingly, the necessary annihilation cross section for the observed gamma-ray flux provides a good fit to the value for the relic abundance of dark matter. We identify the preferred parameter space of the model after taking the existing experimental constraints from the precision measurements including the muon $(g-2)$, tau decay, neutrino trident production, dark matter direct detection, and the LHC experiments.
We discuss a high-scale SUSY breaking scenario with the wino dark matter in the five-dimensional supergravity model on $S^1/Z_2$. The extra U(1) symmetries broken by the orbifold projection control the flavor structure of soft SUSY-breaking parameters as well as the Yukawa couplings, and a scalar component of the one of moduli multiplets, which arise from extra-dimensional components of the U(1) vector multiplets, induces the slow-roll inflation. Because of the supersymmetric moduli stabilization as well as the moduli inflation, it is found that the correct dark matter relic abundance is non-thermally generated by the gravitino decaying into the wino.
Bekenstein has put forward the idea that, in a quantum theory of gravity, a black hole should have a discrete energy spectrum with concomitant discrete line emission. The quantized black-hole radiation spectrum is expected to be very different from Hawking's semi-classical prediction of a thermal black-hole radiation spectrum. One naturally wonders: Is it possible to reconcile the {\it discrete} quantum spectrum suggested by Bekenstein with the {\it continuous} semi-classical spectrum suggested by Hawking ? In order to address this fundamental question, in this essay we shall consider the zero-point quantum-gravity fluctuations of the black-hole spacetime. In a quantum theory of gravity, these spacetime fluctuations are closely related to the characteristic gravitational resonances of the corresponding black-hole spacetime. Assuming that the energy of the black-hole radiation stems from these zero-point quantum-gravity fluctuations of the black-hole spacetime, we derive the effective temperature of the quantized black-hole radiation spectrum. Remarkably, it is shown that this characteristic temperature of the {\it discrete} (quantized) black-hole radiation agrees with the well-known Hawking temperature of the {\it continuous} (semi-classical) black-hole spectrum.
We study the relativistic dynamics of a pressure-less and irrotational fluid of dark matter (CDM) with a cosmological constant ($\Lambda$), up to second order in cosmological perturbation theory. In our analysis we also account for primordial non-Gaussianity. We consider three gauges: the synchronous-comoving gauge, the Poisson gauge and the total matter gauge, where the first is the unique relativistic Lagrangian frame of reference, and the latters are convenient choices for Eulerian frames. Our starting point is the metric and fluid variables in the Poisson gauge. We then perform a gauge-transformation to the synchronous-comoving gauge, and subsequently to the total matter gauge. Our expressions for the metrics, densities, velocities, and the gauge generators are novel and coincide with known results in the limit of a vanishing cosmological constant.
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In light of recent findings from the kinematic morphology-density relation, we investigate whether the same trends exist in the original morphology density relation, using the same data as Dressler. In addition to Dressler's canonical relations, we find that further refinements are possible when considering the average local projected density of galaxies in a cluster. Firstly, the distribution of ellipticals in a cluster depends on the relative local density of galaxies in that cluster: equivalent rises in the elliptical fraction occur at higher local densities for clusters with higher average local densities. This is not true for the late-type fraction, where the variation with local density within a cluster is independent of the average local density of galaxies in that cluster, and is as Dressler originally found. Furthermore, the overall ratio of ellipticals to early-types in a cluster does not depend on the average density of galaxies in that cluster (unlike the ratio of lenticulars to disk systems), and is fixed at around 30%. In the paradigm of fast and slow rotators, we show that such an elliptical fraction in the early-type population is consistent with a slow rotator fraction of 15% in the early-type population, using the statistics of the ATLAS3D survey. We also find the scatter in the overall ratio of ellipticals to early-types is greatest for clusters with lower average densities, such that clusters with the highest elliptical fractions have the lowest average local densities. Finally, we show that average local projected density correlates well with global projected density, but the latter has difficulty in accurately characterising the density of irregular cluster morphologies.
Stars with a different vertical motion relative to the galactic disk have a different average acceleration. According to Modified Newtonian Dynamics (MOND) theories they should therefore have a different average orbital velocity while revolving around the Milky Way. We show that this property can be used to constrain MOND theories by studying stars in the local neighborhood. With the Hipparcos dataset we can only place marginal constraints. However, the forthcoming GAIA catalogue with its significantly fainter cutoff should allow placing a stringent constraint. The method cannot be used to prove MOND, since halo stars can contribute a similar signal which would be hard to discern.
In our recent investigation of the Oosterhoff dichotomy in the multiple population paradigm (Jang et al. 2014), we have suggested that the RR Lyrae variables in the Oosterhoff groups I, II, and III globular clusters (GCs) are produced mostly by the first, second, and third generation stars (G1, G2, and G3), respectively. Here we show, for the first time, that the observed dichotomies in the inner and outer halo GCs can be naturally reproduced when these models are extended to all metallicity regimes, while maintaining reasonable agreements in the horizontal-branch type versus [Fe/H] correlations. In order to achieve this, however, specific star formation histories are required for the inner and outer halos. In the inner halo GCs, the star formation commenced and ceased earlier with relatively short formation timescale between the subpopulations (~0.5 Gyr), while in the outer halo, the formation of G1 was delayed by ~0.8 Gyr with more extended timescale between G1 and G2 (~1.4 Gyr). This is consistent with the dual origin of the Milky Way halo. Despite the difference in detail, our models show that the Oosterhoff period groups observed in both outer and inner halo GCs are all manifestations of the "population-shift" effect within the instability strip, for which the origin can be traced back to the two or three discrete episodes of star formation in GCs.
We introduce a dust model for cosmological simulations implemented in the moving-mesh code AREPO and present a suite of cosmological hydrodynamical zoom-in simulations to study dust formation within galactic haloes. Our model accounts for the stellar production of dust, accretion of gas-phase metals onto existing grains, destruction of dust through local supernova activity, and dust driven by winds from star-forming regions. We find that accurate stellar and active galactic nuclei feedback is needed to reproduce the observed dust-metallicity relation and that dust growth largely dominates dust destruction. Our simulations predict a dust content of the interstellar medium which is consistent with observed scaling relations at $z = 0$, including scalings between dust-to-gas ratio and metallicity, dust mass and gas mass, dust-to-gas ratio and stellar mass, and dust-to-stellar mass ratio and gas fraction. We find that roughly two-thirds of dust at $z = 0$ originated from Type II supernovae, with the contribution from asymptotic giant branch stars below 20 per cent for $z \gtrsim 5$. While our suite of Milky Way-sized galaxies forms dust in good agreement with a number of key observables, it predicts a high dust-to-metal ratio in the circumgalactic medium, which motivates a more realistic treatment of thermal sputtering of grains and dust cooling channels.
The outer halo regions of early-type galaxies carry key information about their past accretion history. However, spectroscopically probing the stellar component at such galactocentric radii is still challenging. Using Keck/DEIMOS, we have been able to measure the metallicities of the stellar and globular cluster components in 12 early-type galaxies out to more than $10~\rm{R_{e}}$. We find similar metallicity gradients for the metal-poor and metal-rich globular cluster subpopulations, suggesting a common formation process for the two subpopulations. This is in conflict with most current theoretical predictions, where the metal-poor globular clusters are thought to be purely accreted and metal-rich globular clusters mostly formed in-situ. Moreover, we find that the globular cluster metallicity gradients show a trend with galaxy mass, being steeper in lower-mass galaxies than in higher-mass galaxies. This is similar to what we find for the outermost galaxy stars and suggests a more active accretion history, with a larger role played by major mergers, in the most massive galaxies. This conclusion is qualitatively consistent with expectations from two-phase galaxy assembly models. Finally, we find that the small difference in metallicity between galaxy stars and metal-rich globular clusters at $1~\rm{R_{e}}$ may correlate with galaxy mass. The origin of this difference is not currently clear.
A recent reanalysis of archival data has lead several authors to arrive at strikingly different conclusions for a number of planet-hosting candidate stars. In particular, some radial velocities measured using FEROS spectra have been shown to be inaccurate, throwing some doubt on the validity of a number of planet detections. Motivated by these results, we have begun the Reanalysis of Archival FEROS specTra (RAFT) program and here we discuss the first results from this work. We have reanalyzed FEROS data for the stars HD 11977, HD 47536, HD 70573, HD 110014 and HD 122430, all of which are claimed to have at least one planetary companion. We have reduced the raw data and computed the radial velocity variations of these stars, achieving a long-term precision of ~ 10 m/s on the known stable star tau Ceti, and in good agreement with the residuals to our fits. We confirm the existence of planets around HD 11977, HD 47536 and HD 110014, but with different orbital parameters than those previously published. In addition, we found no evidence of the second planet candidate around HD 47536, nor any companions orbiting HD 122430 and HD 70573. Finally, we report the discovery of a second planet around HD 110014, with a minimum mass of 3.1 Mjup and a orbital period of 130 days. Analysis of activity indicators allow us to confirm the reality of our results and also to measure the impact of magnetic activity on our radial velocity measurements. These results confirm that very metal-poor stars down to [Fe/H]~ -0.7 dex, can indeed form giant planets given the right conditions.
It has been recently found that the characteristic photometric parameters of antitruncated discs in S0 galaxies follow tight scaling relations. We investigate if similar scaling relations are satisfied by galaxies of other morphological types. We have analysed the trends in several photometric planes relating the characteristic surface brightness and scalelengths of the breaks and the inner and outer discs of local antitruncated S0-Scd galaxies, using published data and fits performed to the surface brightness profiles of two samples of Type-III galaxies in the R and Spitzer 3.6 microns bands. We have performed linear fits to the correlations followed by different galaxy types in each plane, as well as several statistical tests to determine their significance. We have found that: 1) the antitruncated discs of all galaxy types from Sa to Scd obey tight scaling relations both in R and 3.6 microns, as observed in S0s; 2) the majority of these correlations are significant accounting for the numbers of the available data samples; 3) the trends are clearly linear when the characteristic scalelengths are plotted on a logarithmic scale; and 4) the correlations relating the characteristic surface brightnesses of the inner and outer discs and the breaks with the various characteristic scalelengths significantly improve when the latter are normalized to the optical radius of the galaxy. The results suggest that the scaling relations of Type-III discs are independent of the morphological type and the presence (or absence) of bars within the observational uncertainties of the available datasets, although larger and deeper samples are required to confirm this. The tight structural coupling implied by these scaling relations impose strong constraints on the mechanisms proposed for explaining the formation of antitruncated stellar discs in the galaxies across the whole Hubble Sequence (Abridged).
We investigate the ability of current implementations of galaxy group finders to recover colour-dependent halo occupation statistics. To test the fidelity of group catalogue inferred statistics, we run three different group finders used in the literature over a mock that includes galaxy colours in a realistic manner. Overall, the resulting mock group catalogues are remarkably similar, and most colour-dependent statistics are recovered with reasonable accuracy. However, it is also clear that certain systematic errors arise as a consequence of correlated errors in group membership determination, central/satellite designation, and halo mass assignment. We introduce a new statistic, the halo transition probability (HTP), which captures the combined impact of all these errors. As a rule of thumb, errors tend to equalize the properties of distinct galaxy populations (i.e. red vs. blue galaxies or centrals vs. satellites), and to result in inferred occupation statistics that are more accurate for red galaxies than for blue galaxies. A statistic that is particularly poorly recovered from the group catalogues is the red fraction of central galaxies as function of halo mass. Group finders do a good job in recovering galactic conformity, but also have a tendency to introduce weak conformity when none is present. We conclude that proper inference of colour-dependent statistics from group catalogues is best achieved using forward modelling (i.e., running group finders over mock data), or by implementing a correction scheme based on the HTP, as long as the latter is not too strongly model-dependent.
We present a study of the recent star formation of 30 Doradus in the Large Magellanic Cloud (LMC) using the panchromatic imaging survey Hubble Tarantula Treasury Project (HTTP). In this paper we focus on the stars within 20 pc of the center of the massive ionizing cluster of 30 Doradus, NGC 2070. We recovered the star formation history by comparing deep optical and NIR color-magnitude diagrams (CMDs) with state-of-the-art synthetic CMDs generated with the latest PARSEC models, which include all stellar phases from pre-main sequence to post- main sequence. For the first time in this region we are able to measure the star formation using intermediate and low mass stars simultaneously. Our results suggest that NGC2070 experienced a prolonged activity. In particular, we find that the star formation in the region: i) exceeded the average LMC rate ~ 20 Myr ago; ii) accelerated dramatically ~ 7 Myr ago; and iii) reached a peak value 1-3 Myr ago. We did not find significant deviations from a Kroupa initial mass function down to 0.5 Msun. The average internal reddening E(B-V) is found to be between 0.3 and 0.4 mag.
Reverberation mapping is now a well-established technique for investigating spatially-unresolved structures in the nuclei of distant galaxies with actively-accreting supermassive black holes. Structural parameters for the broad emission-line region, with angular sizes of microarcseconds, can be constrained through the substitution of time resolution for spatial resolution. Many reverberation experiments over the last 30 years have led to a practical understanding of the requirements necessary for a successful program. With reverberation measurements now in hand for 60 active galaxies, and more on the horizon, we are able to directly constrain black hole masses, derive scaling relationships that allow large numbers of black hole mass estimates throughout the observable Universe, and begin investigating the detailed geometry and kinematics of the broad line region. Reverberation mapping is therefore one of the few techniques available that will allow a deeper understanding of the physical mechanisms involved in AGN feeding and feedback at very small scales, as well as constraints on the growth and evolution of black holes across cosmic time. In this contribution, I will briefly review the background, implementation, and major results derived from this high angular resolution technique.
The efficiency of dust formation in oxygen-rich AGB stars should (in theory) be metallicity dependent since they are not producing their own raw material for dust production. Metal-poor carbon stars may not be very efficient dust producers either, because of more radiative heating of the grains forming in their atmospheres. We have just confirmed that inefficient dust and wind formation in simulations of metal-poor carbon stars is a real physical effect, albeit within the limitations of our simulations. Taken at face value, this implies that the amount of dust supplied by low-metallicity AGB stars to the build up of the cosmic dust component is clearly limited. Consequently, one may also ask how large a contribution AGB stars can make in general, when compared to recent observations of cosmic dust, which are suggesting major contributions from other sources?
We study the baryon content of low mass galaxies selected from the Sloan Digital Sky Survey (SDSS DR8), focusing on galaxies in isolated environments where the complicating physics of galaxy-galaxy interactions are minimized. We measure neutral hydrogen (HI) gas masses and line-widths for 148 isolated galaxies with stellar mass between $10^7$ and $10^{9.5} M_{\odot}$. We compare isolated low mass galaxies to more massive galaxies and galaxies in denser environments by remeasuring HI emission lines from the Arecibo Legacy Fast ALFA (ALFALFA) survey 40% data release. All isolated low mass galaxies either have large atomic gas fractions or large atomic gas fractions cannot be ruled out via their upper limits. We measure a median atomic gas fraction of $f_{\rm gas} = 0.82 \pm 0.13$ for our isolated low mass sample with no systems below 0.30. At all stellar masses, the correlations between galaxy radius, baryonic mass and velocity width are not significantly affected by environment. Finally, we estimate a median baryon to total dynamical mass fraction of $f_{\rm baryon, disk} = 0.15 \pm 0.18$. We also estimate two different median baryon to halo mass fractions using the results of semi-analytic models $(f_{\rm baryon, halo} = 0.04 \pm 0.06)$ and abundance matching $(f_{\rm baryon, halo} = 0.04 \pm 0.02)$. Baryon fractions estimated directly using HI observations appear independent of environment and maximum circular velocity, while baryon fractions estimated using abundance matching show a significant depletion of baryons at low maximum circular velocities.
I briefly review advances in the understanding and modeling of relativistic stellar dynamics around massive black holes (MBHs) in galactic nuclei, following the inclusion of coherent relaxation and of secular processes in a new formal analytic description of the dynamics.
The sunspot activity is the end result of the cyclic destruction and regeneration of magnetic fields by the dynamo action. We propose a new method to analyze the daily sunspot areas data recorded since 1874. By computing the power spectral density of daily data series using the Mexican hat wavelet, we found a power spectrum with a well-defined shape, characterized by three features. The first term is the 22 yr solar magnetic cycle, estimated in our work to be of 18.43 yr. The second term is related to the daily volatility of sunspots. This term is most likely produced by the turbulent motions linked to the solar granulation. The last term corresponds to a periodic source associated with the solar magnetic activity, for which the maximum of power spectral density occurs at 22.67 days. This value is part of the 22-27 day periodicity region that shows an above-average intensity in the power spectra. The origin of this 22.67 day periodic process is not clearly identified, and there is a possibility that it can be produced by convective flows inside the star. The study clearly shows a north-south asymmetry. The 18.43 yr periodical source is correlated between the two hemispheres, but the 22.67 day one is not correlated. It is shown that towards the large timescales an excess occurs in the northern hemisphere, especially near the previous two periodic sources. To further investigate the 22.67 day periodicity we made a Lomb-Scargle spectral analysis. The study suggests that this periodicity is distinct from others found nearby.
HERO (Hybrid Evaluator for Radiative Objects) is a 3D general relativistic radiative transfer code which has been tailored to the problem of analyzing radiation from simulations of relativistic accretion discs around black holes. HERO is designed to be used as a postprocessor. Given some fixed fluid structure for the disc (i.e. density and velocity as a function of position from a hydrodynamics or magnetohydrodynamics simulation), the code obtains a self-consistent solution for the radiation field and for the gas temperatures using the condition of radiative equilibrium. The novel aspect of HERO is that it combines two techniques: 1) a short characteristics (SC) solver that quickly converges to a self consistent disc temperature and radiation field, with 2) a long characteristics (LC) solver that provides a more accurate solution for the radiation near the photosphere and in the optically thin regions. By combining these two techniques, we gain both the computational speed of SC and the high accuracy of LC. We present tests of HERO on a range of 1D, 2D and 3D problems in flat space and show that the results agree well with both analytical and benchmark solutions. We also test the ability of the code to handle relativistic problems in curved space. Finally, we discuss the important topic of ray-defects, a major limitation of the SC method, and describe our strategy for minimizing the induced error.
The initial success of the Rigidly Rotating Magnetosphere (RRM) model application to the B2Vp star sigma OriE by Townsend, Owocki & Groote (2005) triggered a renewed era of observational monitoring of this archetypal object. We utilize high-resolution spectropolarimetry and the magnetic Doppler imaging (MDI) technique to simultaneously determine the magnetic configuration, which is predominately dipolar, with a polar strength Bd = 7.3-7.8 kG and a smaller non-axisymmetric quadrupolar contribution, as well as the surface distribution of abundance of He, Fe, C, and Si. We describe a revised RRM model that now accepts an arbitrary surface magnetic field configuration, with the field topology from the MDI models used as input. The resulting synthetic Ha emission and broadband photometric observations generally agree with observations, however, several features are poorly fit. To explore the possibility of a photospheric contribution to the observed photometric variability, the MDI abundance maps were used to compute a synthetic photospheric light curve to determine the effect of the surface inhomogeneities. Including the computed photospheric brightness modulation fails to improve the agreement between the observed and computed photometry. We conclude that the discrepancies cannot be explained as an effect of inhomogeneous surface abundance. Analysis of the UV light variability shows good agreement between observed variability and computed light curves, supporting the accuracy of the photospheric light variation calculation. We thus conclude that significant additional physics is necessary for the RRM model to acceptably reproduce observations of not only sigma Ori E, but also other similar stars with significant stellar wind-magnetic field interactions.
A classical nova occurs when material accreting onto the surface of a white dwarf in a close binary system ignites in a thermonuclear runaway. Complex structures observed in the ejecta at late stages could result from interactions with the companion during the common envelope phase. Alternatively, the explosion could be intrinsically bipolar, resulting from a localized ignition on the surface of the white dwarf or as a consequence of rotational distortion. Studying the structure of novae during the earliest phases is challenging because of the high spatial resolution needed to measure their small sizes. Here we report near-infrared interferometric measurements of the angular size of Nova Delphini 2013, starting from one day after the explosion and continuing with extensive time coverage during the first 43 days. Changes in the apparent expansion rate can be explained by an explosion model consisting of an optically thick core surrounded by a diffuse envelope. The optical depth of the ejected material changes as it expands. We detect an ellipticity in the light distribution, suggesting a prolate or bipolar structure that develops as early as the second day. Combining the angular expansion rate with radial velocity measurements, we derive a geometric distance to the nova of 4.54 +/- 0.59 kpc from the Sun.
Using self-consistent three-dimensional (3D) N-body simulations, we investigate the physical properties of non-axisymmetric features in a disk galaxy created by a tidal interaction with its companion. The primary galaxy consists of a stellar disk, a bugle, and a live halo, corresponding to Milky-Way type galaxies, while the companion is represented by a halo alone. We vary the companion mass and the pericenter distance to explore situations with differing tidal strength parameterized by either the relative tidal force P or the relative imparted momentum S. We find that the formation of a tidal tail in the outer parts requires P > 0.05 or S > 0.07. A stronger interaction results in a stronger, less wound tail that forms earlier. Similarly, a stronger tidal forcing produces stronger, more loosely wound spiral arms in the inner parts. The arms are approximately logarithmic in shape, with both amplitude and pitch angle decaying with time. The derived pattern speed decreases with radius and is close to the Omega-kappa/2 curve at late time, with Omega and kappa denoting the angular and epicycle frequencies, respectively. This suggests that the tidally-induced spiral arms are most likely kinematic density waves weakly modified by self-gravity. Compared to the razor-thin counterparts, arms in the 3D models are weaker, have a smaller pitch angle, and wind and decay more rapidly. The 3D density structure of the arms is well described by the concentrated and sinusoidal models when the arms are in the nonlinear and linear regimes, respectively. We demonstrate that dynamical friction between interacting galaxies transfers the orbital angular momentum of one galaxy to the spin angular momentum of the companion halo.
A search for high-energy neutrinos coming from the direction of the Galactic Centre is performed using the data recorded by the ANTARES neutrino telescope from 2007 to 2012. The event selection criteria are chosen to maximise the sensitivity to possible signals produced by the self-annihilation of weakly interacting massive particles accumulated around the centre of the Milky Way with respect to the atmospheric background. After data unblinding, the number of neutrinos observed in the line of sight of the Galactic Centre is found to be compatible with background expectations. The 90% C.L. upper limits in terms of the neutrino+anti-neutrino flux, $\rm \Phi_{\nu_{\mu}+\bar{\nu}_\mu}$, and the velocity averaged annihilation cross-section, $\rm <\sigma_{A}v>$, are derived for the WIMP self-annihilation channels into $\rm b\bar{b},W^{+}W^{-},\tau^{+}\tau^{-},\mu^{+}\mu^{-},\nu\bar{\nu}$. The ANTARES limits for $\rm <\sigma_{A}v>$ are shown to be the most stringent for a neutrino telescope over the WIMP masses $\rm 25\,GeV < M_{WIMP} < 10\,TeV$.
A Coronal Mass Ejection (CME) is an inhomogeneous structure consisting of different features which evolve differently with the propagation of the CME. Simultaneous heliospheric tracking of different observed features of a CME can improve our understanding about relative forces acting on them. It also helps to estimate accurately their arrival times at the Earth and identify them in in- situ data. This also enables to find association between remotely observed features and in-situ observations near the Earth. In this paper, we attempt to continuously track two density enhanced features, one at the front and another at the rear edge of the 6 October 2010 CME. This is achieved by using time-elongation maps constructed from STEREO/SECCHI observations. We derive the kinematics of the tracked features using various reconstruction methods. The estimated kinematics are used as inputs in the Drag Based Model (DBM) to estimate the arrival time of the tracked features of the CME at L1. On comparing the estimated kinematics as well as the arrival times of the remotely observed features with in-situ observations by ACE and Wind, we find that the tracked bright feature in the J-map at the rear edge of 6 October 2010 CME corresponds most probably to the enhanced density structure after the magnetic cloud detected by ACE and Wind. In-situ plasma and compositional parameters provide evidence that the rear edge density structure may correspond to a filament associated with the CME while the density enhancement at the front corresponds to the leading edge of the CME. Based on this single event study, we discuss the relevance and significance of heliospheric imager (HI) observations in identification of the three-part structure of the CME.
Structural properties posses valuable information about the formation and evolution of galaxies, and are important for understanding the past, present, and future universe. Here we use unsupervised machine learning methodology to analyze a network of similarities between galaxy morphological types, and automatically deduce a morphological sequence of galaxies. Application of the method to the EFIGI catalog show that the morphological scheme produced by the algorithm is largely in agreement with the De Vaucouleurs system, demonstrating the ability of computer vision and machine learning methods to automatically profile galaxy morphological sequences. The unsupervised analysis method is based on comprehensive computer vision techniques that compute the visual similarities between the different morphological types. Rather than relying on human cognition, the proposed system deduces the similarities between sets of galaxy images in an automatic manner, and is therefore not limited by the number of galaxies being analyzed. The source code of the method is publicly available, and the protocol of the experiment is included in the paper so that the experiment can be replicated, and the method can be used to analyze user-defined datasets of galaxy images.
We present a sample of about 120,000 red clump candidates selected from the LAMOST DR2 catalog based on the empirical distribution model in the effective temperature vs. surface gravity plane. Although, in general, red clump stars are considered as the standard candle, they do not exactly stay in a narrow range of absolute magnitude, but may extend to more than 1 magnitude depending on their initial mass. Consequently, conventional oversimplified distance estimations with assumption of fixed luminosity may lead to systematic bias related to the initial mass or the age, which may potentially affect the study of the evolution of the Galaxy with red clump stars. We therefore employ an isochrone-based method to estimate the absolute magnitude of red clump stars from their observed surface gravities, effective temperatures, and metallicities. We verify that the estimation well removes the systematics and provide an initial mass/age independent distance estimates with accuracy less than 10%.
Helioseismology has taught us a great deal about the stratification and kinematics of the solar interior, sufficient for us to embark upon dynamical studies more detailed than have been possible before. The most sophisticated studies to date have been the very impressive numerical simulations of the convection zone, from which, especially in recent years, a great deal has been learnt. Those simulations, and the seismological evidence with which they are being confronted, are reviewed elsewhere in this volume. Our understanding of the global dynamics of the radiative interior of the Sun is in a much more primitive state. Nevertheless, some progress has been made, and seismological inference has provided us with evidence of more to come. Some of that I summarize here, mentioning in passing hints that are pointing the way to the future.
The magnetorotational instability (MRI) drives vigorous turbulence in a region of protoplanetary disks where the ionization fraction is sufficiently high. It has recently been shown that the electric field induced by the MRI can heat up electrons and thereby affect the ionization balance in the gas. In particular, in a disk where abundant dust grains are present, the electron heating causes a reduction of the electron abundance, thereby preventing further growth of the MRI. By using the nonlinear Ohm's law that takes into account electron heating, we investigate where in protoplanetary disks this negative feedback between the MRI and ionization chemistry becomes important. We find that the "e-heating zone," the region where the electron heating limits the saturation of the MRI, extends out to 80 AU in the minimum-mass solar nebula with abundant submicron-sized grains. This region is considerably larger than the conventional dead zone whose radial extent is $\sim20$ AU in the same disk model. Our simple estimate based on the scaling between the Maxwell stress and current density shows that that the MRI turbulence in the e-heating zone should have a significantly low saturation level, with the viscosity parameter $\alpha$ being from $10^{-5}$ to $10^{-3}$ at the midplane. This implies that the MRI should be "virtually dead" deep inside the e-heating zone. We also find that (sub)micron-sized grains in the e-heating zone are so negatively charged that their collisional growth is unlikely to occur.
Coronagraphic imagery of the circumstellar disk around HD 169142 in H-band polarized intensity (PI) with Subaru/HiCIAO is presented. The emission scattered by dust particles at the disk surface in 0.2" <= r <= 1.2", or 29 <= r <= 174 AU, is successfully detected. The azimuthally-averaged radial profile of the PI shows a double power-law distribution, in which the PIs in r=29-52 AU and r=81.2-145 AU respectively show r^{-3}-dependence. These two power-law regions are connected smoothly with a transition zone (TZ), exhibiting an apparent gap in r=40-70 AU. The PI in the inner power-law region shows a deep minimum whose location seems to coincide with the point source at \lambda = 7 mm. This can be regarded as another sign of a protoplanet in TZ. The observed radial profile of the PI is reproduced by a minimally flaring disk with an irregular surface density distribution or with an irregular temperature distribution or with the combination of both. The depletion factor of surface density in the inner power-law region (r< 50 AU) is derived to be <= 0.16 from a simple model calculation. The obtained PI image also shows small scale asymmetries in the outer power-law region. Possible origins for these asymmetries include corrugation of the scattering surface in the outer region, and shadowing effect by a puffed up structure in the inner power-law region.
In the last decade, a combination of high sensitivity, high spatial resolution observations and of coordinated multi-wavelength surveys has revolutionized our view of extra-galactic black hole (BH) astrophysics. We now know that supermassive black holes reside in the nuclei of almost every galaxy, grow over cosmological times by accreting matter, interact and merge with each other, and in the process liberate enormous amounts of energy that influence dramatically the evolution of the surrounding gas and stars, providing a powerful self-regulatory mechanism for galaxy formation. The different energetic phenomena associated to growing black holes and Active Galactic Nuclei (AGN), their cosmological evolution and the observational techniques used to unveil them, are the subject of this chapter. In particular, I will focus my attention on the connection between the theory of high-energy astrophysical processes giving rise to the observed emission in AGN, the observable imprints they leave at different wavelengths, and the methods used to uncover them in a statistically robust way. I will show how such a combined effort of theorists and observers have led us to unveil most of the SMBH growth over a large fraction of the age of the Universe, but that nagging uncertainties remain, preventing us from fully understating the exact role of black holes in the complex process of galaxy and large-scale structure formation, assembly and evolution.
We report the discovery of a new ultra-faint Milky Way satellite candidate, Horologium II, detected in the Dark Energy Survey Y1A1 public data. Horologium II features a half light radius of $r_{h}=47\pm10$ pc and a total luminosity of $M_{V}=-2.6^{+0.2}_{-0.3}$ that place it in the realm of ultra-faint dwarf galaxies on the size-luminosity plane. The stellar population of the new satellite is consistent with an old ($\sim13.5$ Gyr) and metal-poor ([Fe/H]$\sim-2.1$) isochrone at a distance modulus of $(m-M)=19.46$, or a heliocentric distance of 78 kpc, in the color-magnitude diagram. Horologium II has a distance similar to the Sculptor dwarf spheroidal galaxy (79 kpc) and the recently reported ultra-faint satellites Eridanus III (87 kpc) and Horologium I (79 kpc). All four satellites are well aligned on the sky, which suggests a possible common origin. As Sculptor is moving on a retrograde orbit within the Vast Polar Structure when compared to the other classical MW satellite galaxies including the Magellanic Clouds, this hypothesis can be tested once proper motion measurements become available.
Local starbursts have a higher efficiency of converting gas into stars, as compared to typical star-forming galaxies at a given stellar mass, possibly indicative of different modes of star formation. With the peak epoch of galaxy formation occurring at z > 1, it remains to be established whether such an efficient mode of star formation is occurring at high-redshift. To address this issue, we measure the CO molecular gas content of seven high-redshift starburst galaxies with ALMA and IRAM/PdBI. Our sample is selected from the FMOS-COSMOS near-infrared spectroscopic survey of star-forming galaxies at z ~ 1.6 with Subaru. All galaxies have star formation rates (~300-800 Msolar/yr) elevated, by at least four times, above the star-forming main sequence. We detect CO emission in all cases at high significance, indicative of plentiful gas supplies (f_gas ~ 30-50%). Even more compelling, we firmly establish for the first time that starbursts at high redshift systematically have a lower ratio of CO to total infrared luminosity as compared to typical 'main-sequence' star-forming galaxies, although with an offset less than expected based on past studies of local starbursts. We put forward a hypothesis that there exists a continuous increase in star formation efficiency with elevation from the main sequence with galaxy mergers as a possible physical driver. In support of this scenario, our high-redshift sample is similar in other respects to local starbursts such as being metal rich and having a higher ionization state of the ISM.
If the origin of high energy backgrounds of neutrinos, gamma rays, and cosmic ray positrons, is the decay of mesons produced in high energy collisions of the primary cosmic rays with matter inside the cosmic accelerators, then their fluxes, spectra and sky distributions are simply related. Here we show, that the flux of astronomical neutrinos above 35 TeV measured with IceCube is that expected from the sub-TeV gamma ray background measured with Fermi-LAT, and that the Galactic gamma ray background itself is that expected from the flux of sub-TeV CR positrons measured with AMS. These successful relations, without the use of any free adjustable parameters, indicate that the high energy neutrino, gamma ray, and positron backgrounds have a common origin - hadronic meson production by cosmic rays that takes place mostly inside the cosmic ray accelerators rather than in the interstellar medium of galaxies or through the decay/annihilation of dark matter particles.
We study the H2 molecular content in high redshift damped Lyman-alpha systems (DLAs) as a function of the HI column density. We find a significant increase of the H2 molecular content around log N(HI) (cm^-2)~21.5-22, a regime unprobed until now in intervening DLAs, beyond which the majority of systems have log N(H2) > 17. This is in contrast with lines of sight towards nearby stars, where such H2 column densities are always detected as soon as log N(HI)>20.7. This can qualitatively be explained by the lower average metallicity and possibly higher surrounding UV radiation in DLAs. However, unlike in the Milky Way, the overall molecular fractions remain modest, showing that even at a large N(HI) only a small fraction of overall HI is actually associated with the self-shielded H2 gas. Damped Lyman-alpha systems with very high-N(HI) probably arise along quasar lines of sight passing closer to the centre of the host galaxy where the gas pressure is higher. We show that the colour changes induced on the background quasar by continuum (dust) and line absorption (HI Lyman and H2 Lyman & Werner bands) in DLAs with log N(HI)~22 and metallicity ~1/10 solar is significant, but not responsible for the long-discussed lack of such systems in optically selected samples. Instead, these systems are likely to be found towards intrinsically fainter quasars that dominate the quasar luminosity function. Colour biasing should in turn be severe at higher metallicities.
The far-infrared and submillimeter portions of the electromagnetic spectrum provide a unique view of the astrophysical processes present in the early universe. Micro-Spec ($\mu$-Spec), a high-efficiency direct-detection spectrometer concept working in the 450-1000-$\mu$m wavelength range, will enable a wide range of spaceflight missions that would otherwise be challenging due to the large size of current instruments and the required spectral resolution and sensitivity. This paper focuses on the $\mu$-Spec two-dimensional multimode region, where the light of different wavelengths diffracts and converges onto a set of detectors. A two-step optimization process is used to generate geometrical configurations given specific requirements on spectrometer size, operating spectral range, and performance. The canonically employed focal-plane constraints for the power combiner were removed to probe the design space in its entirety. A new four-stigmatic-point optical design solution is identified and explored for use in far-infrared and submillimeter spectroscopy.
The problem of cosmic-ray scattering in the turbulent electromagnetic fields of the interstellar medium and the solar wind is of great importance due to the variety of applications of the resulting diffusion coefficients. Examples are diffusive shock acceleration, cosmic-ray observations, and, in the solar system, the propagation of coronal mass ejections. In recent years, it was found that the simple diffusive motion that had been assumed for decades is often in disagreement both with numerical and observational results. Here, an overview is given of the interaction processes of cosmic rays and turbulent electromagnetic fields. First, the formation of turbulent fields due to plasma instabilities is treated, where especially the non-linear behavior of the resulting unstable wave modes is discussed. Second, the analytical and the numerical side of high-energy particle propagation will be reviewed by presenting non-linear analytical theories and Monte-Carlo simulations. For the example of the solar wind, the impact of anisotropic and dynamical turbulence models will be discussed. In addition, it will be shown how further complications can be treated that arise from the large-scale magnetic field geometry and turbulent electric fields. The transport properties of energetic particles can thus be calculated for current turbulence models so that they withstand a comparison with measurements taken in the solar wind.
gamma ray altitude control system is an important equipment for deep space exploration and sample return mission, its main purpose is a low altitude measurement of the spacecraft based on Compton Effect at the moment when it lands on extraterrestrial celestial or sampling returns to the Earth land, and an ignition altitude correction of the spacecraft retrograde landing rocket at different landing speeds. This paper presents an ignition altitude correction method of the spacecraft at different landing speeds, based on the number of particles gamma ray reflected field gradient graded. Through the establishment of a theoretical model, its algorithm feasibility is proved by a mathematical derivation and verified by an experiment, and also the adaptability of the algorithm under different parameters is described. The method provides a certain value for landing control of the deep space exploration spacecraft landing the planet surface.
We present images from the Solar Blind Channel on HST that resolve hundreds of far ultraviolet (FUV) emitting stars in two ~1 kpc$^2$ interarm regions of the grand-design spiral M101. The luminosity functions of these stars are compared with predicted distributions from simple star formation histories, and are best reproduced when the star formation rate has declined recently (past 10-50 Myr). This pattern is consistent with stars forming within spiral arms and then streaming into the interarm regions. We measure the diffuse FUV surface brightness after subtracting all of the detected stars, clusters and background galaxies. A residual flux is found for both regions which can be explained by a mix of stars below our detection limit and scattered FUV light. The amount of scattered light required is much larger for the region immediately adjacent to a spiral arm, a bright source of FUV photons.
In order to obtain robust cosmological constraints from Type Ia supernova (SN Ia) data, we have applied Markov Chain Monte Carlo (MCMC) to SN Ia lightcurve fitting. We develop a method for sampling the resultant probability density distributions (pdf) of the SN Ia lightcuve parameters in the MCMC likelihood analysis to constrain cosmological parameters. Applying this method to the Joint Lightcurve Analysis (JLA) data set of SNe Ia, we find that sampling the SN Ia lightcurve parameter pdf's leads to cosmological parameters closer to that of a flat Universe with a cosmological constant, compared to the usual practice of using only the best fit values of the SN Ia lightcurve parameters. Our method will be useful in the use of SN Ia data for precision cosmology.
Major mergers between massive clusters have a profound effect in the intracluster gas, which may be used as a probe of the dynamics of structure formation at the high end of the mass function. An example of such a merger is observed at the northern component of Abell 1758, comprised of two massive sub-clusters separated by approximately 750 kpc. One of the clusters exhibits an offset between the dark matter and the intracluster gas. We aim to determine whether it is possible to reproduce the specific morphological features of this cluster by means of a major merger. We perform dedicated SPH (smoothed particle hydrodynamics) N-body simulations in an attempt to simultaneously recover several observed features of Abell 1758, such as the X-ray morphology and the separation between the two peaks in the projected galaxy luminosity map. We propose a specific scenario for the off-axis collision of two massive clusters. This model adequately reproduces several observed features and suggests that Abell 1758 is seen approximately 0.4 Gyr after the first pericentric passage, and that the clusters are already approaching their maximum separation. This means that their relative velocity is as low as 380 km/s. At the same time, the simulated model entails shock waves of ~4500 km/s, which are currently undetected presumably due to the low-density medium. We explain the difference between these velocities and argue that the predicted shock fronts, while plausible, cannot be detected from currently available data.
We explore the influence of turbulence on the transport of energetic particles by using test-particle simulations. We compute parallel and perpendicular diffusion coefficients for two-component turbulence, isotropic turbulence, a model based on Goldreich-Sridhar scaling, noisy reduced magnetohydrodynamic turbulence, and a noisy slab model. We show that diffusion coefficients have a similar rigidity dependence regardless which turbulence model is used and, thus, we conclude that the influence of turbulence on particle transport is not as strong as originally thought. Only fundamental quantities such as particle rigidity and the Kubo number are relevant. In the current paper we also confirm the unified nonlinear transport theory for noisy slab turbulence. To double-check the validity and accuracy of our numerical results, we use a second test-particle code. We show that both codes provide very similar results confirming the validity of our conclusions.
We have performed \emph{ab initio} neutrino radiation hydrodynamics simulations in three and two spatial dimensions (3D and 2D) of core-collapse supernovae from the same 15 $M_\odot$ progenitor through 440 ms after core bounce. Both 3D and 2D models achieve explosions, however, the onset of explosion (shock revival) is delayed by $\sim$100 ms in 3D relative to the 2D counterpart and the growth of the diagnostic explosion energy is slower. This is consistent with previously reported 3D simulations utilizing iron-core progenitors with dense mantles. In the $\sim$100 ms before the onset of explosion, diagnostics of neutrino heating and turbulent kinetic energy favor earlier explosion in 2D. During the delay, the angular scale of convective plumes reaching the shock surface grows and explosion in 3D is ultimately lead by a single, large-angle plume, giving the expanding shock a directional orientation not dissimilar from those imposed by axial symmetry in 2D simulations. We posit that shock revival and explosion in the 3D simulation may be delayed until sufficiently large plumes form, whereas such plumes form more rapidly in 2D, permitting earlier explosions.
We present bhlight, a numerical scheme for solving the equations of general relativistic radiation magnetohydrodynamics (GRRMHD) using a direct Monte Carlo solution of the frequency-dependent radiative transport equation. bhlight is designed to evolve black hole accretion flows at intermediate accretion rate, in the regime between the classical radiatively efficient disk and the radiatively inefficient accretion flow (RIAF), in which global radiative effects play a sub-dominant but non-negligible role in disk dynamics. We describe the governing equations, numerical method, idiosyncrasies of our implementation, and a suite of test and convergence results. We also describe example applications to radiative Bondi accretion and to a slowly accreting Kerr black hole in axisymmetry.
We investigate non-thermal gravitino production after tribrid inflation in supergravity, which is a variant of supersymmetric hybrid inflation where three fields are involved in the inflationary model and where the inflaton field resides in the matter sector of the theory. In contrast to conventional supersymmetric hybrid inflation, where non-thermal gravitino production imposes severe constraints on the inflationary model, we find that the "non-thermal gravitino problem" is generically absent in models of tribrid inflation, mainly due to two effects: (i) With the inflaton in tribrid inflation (after inflation) being lighter than the waterfall field, the latter has a second decay channel with a much larger rate than for the decay into gravitinos. This reduces the branching ratio for the decay of the waterfall field into gravitinos. (ii) The inflaton generically decays later than the waterfall field, and does not produce gravitinos when it decays. This leads to a dilution of the gravitino population from the decays of the waterfall field. The combination of both effects generically leads to a strongly reduced gravitino production in tribrid inflation.
Although there is overwhelming evidence of dark matter from its gravitational interaction, we still do not know its precise gravitational interaction strength or whether it obeys the equivalence principle. Using the latest available cosmological data and working within the framework of $\Lambda\mbox{CDM}$, we first update the measurement of the Newton's constant for all matter: $G_N=7.26^{+0.27}_{-0.27}\times 10^{-11}\,\mbox{m}^{3}\mbox{kg}^{-1}\mbox{s}^{-2}$, which differs by $2.2 \sigma$ from the standard laboratory-based value. In general relativity, dark matter equivalence principle breaking can be mimicked by a long-range dark matter force mediated by an ultra light scalar field. Using the Planck three year data, we find that the dark matter "fifth-force" strength is constrained to be weaker than $10^{-4}$ of the gravitational force. We also introduce a phenomenological, post-Newtonian two-fluid description to explicitly break the equivalence principle by introducing a difference between dark matter inertial and gravitational masses. Depending on the decoupling time of the dark matter and ordinary matter fluids, the ratio of the dark matter gravitational mass to inertial mass is constrained to be unity at the $10^{-6}$ level.
Inhomogeneous phases may appear when a stress is applied to a system and the system can minimize the free energy breaking the rotational invariance. Various examples are known in Nature of this sort, as the paramagnetic to ferromagnetic phase transition, or the fluid/solid phase transition. If the rotational symmetry is broken down to a discrete symmetry, the system is typically named a crystal. We breifly review crystalline color superconductors, which arise in cold quark matter with mismatched Fermi spheres.
We present a two stage hybrid inflationary scenario in non-minimal supergravity which can predict values of the tensor-to-scalar ratio of the order of few times 0.01. For the parameters considered, the underlying supersymmetric particle physics model possesses two inflationary paths, the trivial and the semi-shifted one. The trivial path is stabilized by supergravity corrections and supports a first stage of inflation with a limited number of e-foldings. The tensor-to-scalar ratio can become appreciable while the value of the scalar spectral index remains acceptable as a result of the competition between the relatively mild supergravity corrections and the strong radiative corrections to the inflationary potential. The additional number of e-foldings required for solving the puzzles of hot big bang cosmology are generated by a second stage of inflation taking place along the semi-shifted path. This is possible only because the semi-shifted path is almost perpendicular to the trivial one and, thus, not affected by the strong radiative corrections along the trivial path and also because the supergravity effects remain mild. At the end of inflation, cosmic strings are produced, which may contribute to the primordial curvature perturbation. The requirement that this contribution be restricted to an acceptable level limits the possible values of the tensor-to-scalar ratio not to exceed about 0.03.
We examine vacuum fluctuations in theories with modified dispersion relations which represent dimensional reduction at high energies. By changing units of energy and momentum we can obtain a description rendering the dispersion relations undeformed and transferring all the non-trivial effects to the integration measure in momentum space. Using this description we propose a general quantization procedure, which should be applicable whether or not the theory explicitly introduces a preferred frame. Based on this scheme we evaluate the power spectrum of quantum vacuum fluctuations. We find that in {\it all} theories which run to 2 dimensions in the ultraviolet the vacuum fluctuations, in the ultraviolet regime, are scale-invariant. This is true in flat space but also for "inside the horizon" modes in an expanding universe. We spell out the conditions upon the gravity theory for this scale-invariance to be preserved as the modes are frozen-in outside the horizon. We also digress on the meaning of dimensionality (in momentum and position space) and suggest that the spectral index could itself provide an operational definition of dimensionality.
We investigate the influence of spatially inhomogeneous chiral symmetry-breaking condensates in a magnetic field background on the equation of state for compact stellar objects. After building a hybrid star composed of nuclear and quark matter using the Maxwell construction, we find, by solving the Tolman-Oppenheimer-Volkoff equations for stellar equilibrium, that our equation of state supports stars with masses around 2 $M_\odot$ for values of the magnetic field that are in accordance with those inferred from magnetar data. The inclusion of a weak vector interaction term in the quark part allows to reach 2 solar masses for relatively small central magnetic fields, making this composition a viable possibility for describing the internal degrees of freedom of this class of astrophysical objects.
Assuming the possibility of existence of a supercivilization we extend the idea of Freeman Dyson considering pulsars instead of stars. It is shown that instead of a spherical shell the supercivilization must use ring-like constructions. We have found that a size of the "ring" should be of the order of $(10^{-4}-10^{-1})$AU with temperature interval $(300-600)$K for relatively slowly rotating pulsars and $(10-350)$AU with temperature interval $(300-700)$K for rapidly spinning neutron stars, respectively. Although for the latter the Dyson construction is unrealistically massive and cannot be considered seriously. Analyzing the stresses in terms of the radiation and wind flows it has been argued that they cannot significantly affect the ring construction, indicating that the search for infrared ring-like sources close to slowly rotating pulsars seems to be quite promising.
Diffusive cosmic-ray transport in nonuniform large-scale magnetic fields in the presence of boundaries is considered. Reflecting and absorbing boundary conditions are derived for a modified telegraph equation with a convective term. Analytical and numerical solutions of illustrative boundary problems are presented. The applicability and accuracy of the telegraph approximation for focused cosmic-ray transport in the presence of boundaries are discussed, and potential applications to modeling cosmic-ray transport are noted.
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We present Hubble Space Telescope UV spectra of the 4.6 h period double white dwarf SDSS J125733.63+542850.5. Combined with Sloan Digital Sky Survey optical data, these reveal that the massive white dwarf (secondary) has an effective temperature T2 = 13030 +/- 70 +/- 150 K and a surface gravity log g2 = 8.73 +/- 0.05 +/- 0.05 (statistical and systematic uncertainties respectively), leading to a mass of M2 = 1.06 Msun. The temperature of the extremely low-mass white dwarf (primary) is substantially lower at T1 = 6400 +/- 37 +/- 50 K, while its surface gravity is poorly constrained by the data. The relative flux contribution of the two white dwarfs across the spectrum provides a radius ratio of R1/R2 = 4.2, which, together with evolutionary models, allows us to calculate the cooling ages. The secondary massive white dwarf has a cooling age of about 1 Gyr, while that of the primary low-mass white dwarf is likely to be much longer, possibly larger than 5 Gyrs, depending on its mass and the strength of chemical diffusion. These results unexpectedly suggest that the low-mass white dwarf formed long before the massive white dwarf, a puzzling discovery which poses a paradox for binary evolution.
High--velocity features (HVF), especially of Ca II, are frequently seen in Type Ia supernovae observed prior to B-band maximum (Bmax). These HVF start at more than 25,000 km/s in the days after first light, and slow to about 18,000 km/s near Bmax. To recreate the Ca II near-infrared triplet (CaNIR) HVF in SN 2011fe, we consider the interaction between a Type Ia supernova and a compact circumstellar shell, employing a hydrodynamic 1-D simulation using FLASH. We generate synthetic spectra from the hydrodynamic results using syn++. We show that the CaNIR HVF and its velocity evolution is better explained by a supernova model interacting with a shell than a model without a shell, and briefly discuss the implications for progenitor models.
We exploit long-baseline ALMA sub-mm observations of the lensed star-forming galaxy SDP 81 at z=3.042 to investigate the properties of inter-stellar medium on scales of 50-100pc. The kinematics of the CO gas within this system are well described by a rotationally-supported disk with an inclination-corrected rotation speed, v=320+/-20km/s and a dynamical mass of M=(3.5+/-1.0)x10^10Mo within a radius of 1.5 kpc. The disk is gas rich and unstable, with a Toomre parameter, Q=0.30+/-0.10 and so should collapse in to star-forming regions with Jeans length L_J~130pc. We identify five star-forming regions within the ISM on these scales and show that their scaling relations between luminosity, line-widths and sizes are significantly offset from those typical of molecular clouds in local Galaxies (Larson's relations). These offsets are likely to be caused by the high external hydrostatic pressure for the interstellar medium (ISM), P/kB=(40+/-20)x10^7K/cm3, which is ~10,000x higher than the typical ISM pressure in the Milky Way. The physical conditions of the star-forming ISM and giant molecular clouds appears to be similar to the those found in the densest environments in the local Universe, such as those in the Galactic center.
We report Hubble Space Telescope/Cosmic Origins Spectrograph observations of the Ly$\alpha$ emission and interstellar absorption lines in a sample of ten star-forming galaxies at z~0.2. Selected on the basis of high equivalent width optical emission lines, the sample, dubbed "Green Peas," make some of the best analogs for young galaxies in an early Universe. We detect Ly$\alpha$ emission in all ten galaxies, and 9/10 show double-peaked line profiles suggestive of low H I column density. We measure Ly$\alpha$/H$\alpha$ flux ratios of 0.5-5.6, implying that 5% to 60% of Ly$\alpha$ photons escape the galaxies. These data confirm previous findings that low-ionization metal absorption (LIS) lines are weaker when Ly$\alpha$ escape fraction and equivalent width are higher. However, contrary to previously favored interpretations of this trend, increased Ly$\alpha$ output cannot be the result of a varying H I covering: the Lyman absorption lines (Ly$\beta$ and higher) show a covering fraction near unity for gas with N_{H I} >~ 10^{16} cm^{-2}. Moreover, we detect no correlation between Ly$\alpha$ escape and the outflow velocity of the LIS lines, suggesting that kinematic effects do not explain the range of Ly$\alpha$/H$\alpha$ flux ratios in these galaxies. In contrast, we detect a strong anti-correlation between the Ly$\alpha$ escape fraction and the velocity separation of the Ly$\alpha$ emission peaks, driven primarily by the velocity of the blue peak. As this velocity separation is sensitive to H I column density, we conclude that Ly$\alpha$ escape in these Green Peas is likely regulated by the H I column density rather than outflow velocity or H I covering fraction.
We present high-resolution 870-um ALMA continuum maps of 30 bright sub-millimeter sources in the UKIDSS UDS field. These sources are selected from deep, 1-square degrees 850-um maps from the SCUBA--2 Cosmology Legacy Survey, and are representative of the brightest sources in the field (median SCUBA2 flux S_850=8.7+/-0.4 mJy). We detect 52 sub-millimeter galaxies (SMGs) at >4-sigma significance in our 30 ALMA maps. In 61+/-17% of the ALMA maps the single-dish source comprises a blend of >=2 SMGs, where the secondary SMGs are Ultra--Luminous Infrared Galaxies (ULIRGs) with L_IR>10^12 Lo. The brightest SMG contributes on average 80+/-4% of the single-dish flux density, and in the ALMA maps containing >=2 SMGs the secondary SMG contributes 25+/-3% of the integrated ALMA flux. We construct source counts and show that multiplicity boosts the apparent single-dish cumulative counts by 20% at S_870>7.5mJy, and by 60% at S_870>12mJy. We combine our sample with previous ALMA studies of fainter SMGs and show that the counts are well-described by a double power-law with a break at 8.5+/-0.6mJy. The break corresponds to a luminosity of ~6x10^12Lsol or a star-formation rate of ~1000Mo/yr. For the typical sizes of these SMGs, which are resolved in our ALMA data with r=1.2+/-0.1kpc, this yields a limiting SFR density of ~100Msol/yr/kpc2. Finally, the number density of S_870>2mJy SMGs is 80+/-30 times higher than that derived from blank-field counts. An over-abundance of faint SMGs is inconsistent with line-of-sight projections dominating multiplicity in the brightest SMGs, and indicates that a significant proportion of these high-redshift ULIRGs must be physically associated.
We present a comprehensive study of spectroscopic radius measurements of twelve neutron stars obtained during thermonuclear bursts or in quiescence. We incorporate, for the first time, a large number of systematic uncertainties in the measurement of the apparent angular sizes, Eddington fluxes, and distances, in the composition of the interstellar medium, and in the flux calibration of X-ray detectors. We also take into account the results of recent theoretical calculations of rotational effects on neutron star radii, of atmospheric effects on surface spectra, and of relativistic corrections to the Eddington critical flux. We employ Bayesian statistical frameworks to obtain neutron star radii from the spectroscopic measurements as well as to infer the equation of state from the radius measurements. Combining these with the results of experiments in the vicinity of nuclear saturation density and the observations of ~2 Msun neutron stars, we place strong and quantitative constraints on the properties of the equation of state between ~2-8 times the nuclear saturation density. We find that around M=1.5 Msun, the preferred equation of state predicts a radius of 10.8-0.4+0.5 km. When interpreting the pressure constraints in the context of high density equations of state based on interacting nucleons, our results suggest a weaker contribution of the three-body interaction potential than previously considered.
Measuring neutron star radii with spectroscopic and timing techniques relies on the combination of multiple observables to break the degeneracies between the mass and radius introduced by general relativistic effects. Here, we explore a frequentist and a Bayesian framework to obtain the most likely value and the uncertainty in such a measurement. We find that, for the expected range of masses and radii and for realistic measurement errors, the frequentist approach suffers from biases that are larger than the accuracy in the radius measurement required to distinguish between the different equations of state. In contrast, in the Bayesian framework, the inferred uncertainties are larger, but the most likely values do not suffer from such biases. We also investigated ways of quantifying the degree of consistency between different spectroscopic measurements from a single source. We showed that a careful assessment of the systematic uncertainties in the measurements eliminates the need for introducing ad hoc biases, which lead to artificially large inferred radii.
A brief set of notes about the database design for 3D maps of dust extinction in the WFAU Archives, which support data from UKIRT-WFCAM, VISTA and VST. The notes also detail typical use cases, such as getting colour-excesses, extinction-corrections, spectral energy distributions and colour-magnitude diagrams and demonstrate the SQL queries to return data, along with examples from VVV DR2 with bulge extinction maps from Chen et al. (2013).
Type Ia supernovae are destructive explosions of carbon oxygen white dwarfs. Although they are used empirically to measure cosmological distances, the nature of their progenitors remains mysterious, One of the leading progenitor models, called the single degenerate channel, hypothesizes that a white dwarf accretes matter from a companion star and the resulting increase in its central pressure and temperature ignites thermonuclear explosion. Here we report observations of strong but declining ultraviolet emission from a Type Ia supernova within four days of its explosion. This emission is consistent with theoretical expectations of collision between material ejected by the supernova and a companion star, and therefore provides evidence that some Type Ia supernovae arise from the single degenerate channel.
We study the environments of 49 WISE/NVSS-selected dusty, hyper-luminous, z~2 quasars using the Atacama Large Millimeter/Sub-millimeter Array (ALMA) 345GHz images. We find that 17 of the 49 WISE/NVSS sources show additional sub-mm galaxies within the ALMA primary beam, probing scales within ~150 kpc. We find a total of 23 additional sub-mm sources, four of which in the field of a single WISE/NVSS source. The measured 870 um source counts are ~10 times expectations for unbiased regions, suggesting such hyper-luminous dusty quasars are excellent at probing high-density peaks.
To study the atomic, molecular and ionized emission of Giant Molecular Clouds (GMCs), we have initiated a Large Program with the VLA: 'THOR - The HI, OH, Recombination Line survey of the Milky Way'. We map the 21cm HI line, 4 OH lines, 19 H_alpha recombination lines and the continuum from 1 to 2 GHz of a significant fraction of the Milky Way (l=15-67deg, |b|<1deg) at ~20" resolution. In this paper, we focus on the HI emission from the W43 star-formation complex. Classically, the HI 21cm line is treated as optically thin with column densities calculated under this assumption. This might give reasonable results for regions of low-mass star-formation, however, it is not sufficient to describe GMCs. We analyzed strong continuum sources to measure the optical depth, and thus correct the HI 21cm emission for optical depth effects and weak diffuse continuum emission. Hence, we are able to measure the HI mass of W43 more accurately and our analysis reveals a lower limit of M=6.6x10^6 M_sun, which is a factor of 2.4 larger than the mass estimated with the assumption of optically thin emission. The HI column densities are as high as N(HI)~150 M_sun/pc^2 ~ 1.9x10^22 cm^-2, which is an order of magnitude higher than for low mass star formation regions. This result challenges theoretical models that predict a threshold for the HI column density of ~10 M_sun/pc^2, at which the formation of molecular hydrogen should set in. By assuming an elliptical layered structure for W43, we estimate the particle density profiles. While at the cloud edge atomic and molecular hydrogen are well mixed, the center of the cloud is strongly dominated by molecular hydrogen. We do not identify a sharp transition between hydrogen in atomic and molecular form. Our results are an important characterization of the atomic to molecular hydrogen transition in an extreme environment and challenges current theoretical models.
We present radio and infrared observations indicating on-going star formation activity inside the $\sim2-5$ pc circumnuclear ring at the Galactic center. Collectively these measurements suggest a continued disk-based mode of on-going star formation has taken place near Sgr A* over the last few million years. First, VLA observations with spatial resolution 2.17$"\times0.81"$ reveal 13 water masers, several of which have multiple velocity components. The presence of interstellar water masers suggests gas densities that are sufficient for self-gravity to overcome the tidal shear of the 4$\times10^6$ \msol\, black hole. Second, SED modeling of stellar sources indicate massive YSO candidates interior to the molecular ring, supporting in-situ star formation near Sgr A* and appear to show a distribution similar to that of the counter-rotating disks of $\sim$100 OB stars orbiting Sgr A*. Some YSO candidates (e.g., IRS~5) have bow shock structures suggesting that they have have gaseous disks that are phototoevaporated and photoionized by the strong radiation field. Third, we detect clumps of SiO (2-1) and (5-4) line emission in the ring based on CARMA and SMA observations. The FWHM and luminosity of the SiO emission is consistent with shocked protostellar outflows. Fourth, two linear ionized features with an extent of $\sim0.8$ pc show blue and redshifted velocities between $+50$ and $-40$ \kms, suggesting protostellar jet driven outflows with mass loss rates of $\sim5\times10^{-5}$ solar mass yr$^{-1}$. Finally, we present the imprint of radio dark clouds at 44 GHz, representing a reservoir of molecular gas that feeds star formation activity close to Sgr A*.
Modified Newtonian dynamics (MoND) is an empirical theory originally proposed to explain the rotation curves of spiral galaxies by modifying the gravitational acceleration, rather than by invoking dark matter. Here, we set constraints on MoND using an up-to-date compilation of kinematic tracers of the Milky Way and a comprehensive collection of morphologies of the baryonic component in the Galaxy. In particular, we find that the so-called "standard" interpolating function cannot explain at the same time the rotation curve of the Milky Way and that of external galaxies for any of the baryonic models studied, while the so-called "simple" interpolating function remains viable for a subset of models. Upcoming astronomical observations will refine our knowledge on the morphology of baryons and will ultimately confirm or rule out the validity of MoND in the Milky Way. We also present constraints on MoND-like theories without making any assumptions on the interpolating function.
The mass spectrum of stellar-mass black holes (BHs) is highly uncertain. Dynamical mass measurements are available only for few ($\sim{}10$) BHs in X-ray binaries, while theoretical models strongly depend on the hydrodynamics of supernova (SN) explosions and on the evolution of massive stars. In this paper, we present and discuss the mass spectrum of compact remnants that we obtained with SEVN, a new public population-synthesis code, which couples the PARSEC stellar evolution tracks with up-to-date recipes for SN explosion (depending on the Carbon-Oxygen mass of the progenitor, on the compactness of the stellar core at pre-SN stage, and on a recent two-parameter criterion based on the dimensionless entropy per nucleon at pre-SN stage). SEVN can be used both as a stand-alone code and in combination with direct-summation N-body codes (Starlab, HiGPUs). The PARSEC stellar evolution tracks currently implemented in SEVN predict significantly larger values of the Carbon-Oxygen core mass with respect to previous models. For most of the SN recipes we adopt, this implies substantially larger BH masses at low metallicity ($\leq{}2\times{}10^{-3}$), than other population-synthesis codes. The maximum BH mass found with SEVN is $\sim{}$25, 60 and 130 M$_{\odot}$ at metallicity $Z =2 \times{} 10^{-2}$ , $2 \times{}10^{-3}$ and $2\times{} 10^{-4}$ , respectively. Mass loss by stellar winds plays a major role in determining the mass of BHs for very massive stars ($\geq{}90$ M$_\odot{}$), while the remnant mass spectrum depends mostly on the adopted SN recipe for lower progenitor masses. We discuss the implications of our results for the transition between NS and BH mass, and for the expected number of massive BHs (with mass $>25$ M$_\odot{}$) as a function of metallicity.
We study the primordial magnetic field generated by the simple model $f^2 FF$ in Starobinsky, $R^2$-inflationary, model. The scale invariant PMF is achieved at relatively high power index of the coupling function, $\left| \alpha \right| \approx 7.44$. This model does not suffer from the backreaction problem as long as, the rate of inflationary expansion, $H$, is in the order of or less than the upper bound reported by Planck ($\le 3.6 \times 10^{-5} M_\rm{Pl}$) in both de Sitter and power law expansion, which show similar results. We calculate the lower limit of the reheating parameter, $R_\rm{rad} > 6.888$ in $R^2$-inflation. Based on the upper limit obtained from CMB, we find that the upper limits of magnetic field and reheating energy density as, $\left(\rho_{B_\rm{end}} \right)_\rm{CMB} < 1.184 \times 10^{-20} M_\rm{Pl}^4$ and $\left(\rho_\rm{reh} \right)_\rm{CMB} < 8.480 \times 10^{-22} M_\rm{Pl}^4$. All of foregoing results are well more than the lower limit derived from WMAP7 for both large and small field inflation. By using the Planck inflationary constraints, 2015 in the context of ${R^2}$-inflation, the upper limit of reheating temperature and energy density for all possible values of $w _\rm{reh}$ are respectively constrained as, $T_\rm{reh} < 4.32 \times 10^{13} \rm{GeV}$ and $\rho_\rm{reh} < 3.259 \times 10^{-18} M_\rm{Pl}^4$ at $n_\rm{s} \approx 0.9674$. This value of spectral index is well consistent with Planck, 2015 results. Adopting $T_\rm{reh}$, enables us to constrain the reheating e-folds number, $N_\rm{reh}$ on the range $1 < N_\rm{reh} < 8.3$, for $- 1/3 < w_\rm{reh} < 1$. By using the scale invariant PMF generated by $f^2 FF$, we find that the upper limit of present magnetic field, $B_0 < 8.058 \times 10^{-9} \rm{G}$.
In this paper, the Smoothed Particle Hydrodynamics (SPH) method is extended to the description of a medium with negative pressure. Under certain circumstances, the SPH method shows an unphysical instability that results in particle clustering. This instability is called the tensile instability. The tensile instability occurs in positive pressure regions in a regular fluid if a very large number of neighbor particles are used with certain shapes of kernel functions, and it is significant in negative pressure regions that emerge in stretched elastic bodies. We must suppress the tensile instability in SPH for calculations of elastic bodies. In this study, we explore a new technique to remove the tensile instability by extending the SPH method that utilizes a Riemann solver (Godunov SPH method) and conducting a linear stability analysis of the equation of motion for the extended method. We find that the tensile instability can be suppressed by choosing an appropriate order of interpolation in the equation of motion of the Godunov SPH method. We also derive an analytic solution for a Riemann solver for a simple equation of state of an elastic body, and construct a Godunov SPH method for the equation of state that allows negative pressure.
We are conducting an archival Swift program to measure multiwavelength variability in active galactic nuclei (AGN). This variability information will provide constraints on the geometry, physical conditions and processes of the structures around the central black holes that emit and reprocess the observed flux. Among our goals are: (1) to produce a catalog of type 1 AGN with time-resolved multi-wavelength data; (2) to characterize variability in the optical, UV and X-ay bands as well as changes in spectral slope; (3) to quantify the impact of variability on multi-wavelength properties; and (4) to measure correlated variability between bands. Our initial efforts have revealed a UVOT calibration issue that can cause a few percent of measured UV fluxes to be anomalously low, by up to 30%.
We present observations and analysis of an unusual [C II] emission line in the very luminous QSO SDSS J155426.16+193703.0 at z~4.6. The line is extremely broad (FWHM 735 km/s) and seems to have a flat-topped or double-peaked line profile. A velocity map of the line shows a gradient across the source that indicates large-scale rotation of star-forming gas. Together, the velocity map and line profile suggest the presence of a massive rotating disc with a dynamical mass M_dyn > 5x10^10 M_sun. Using the assumption of a rotating disc origin, we employ an empirical relation between galaxy disc circular velocity and bulge velocity dispersion (sigma) to estimate that sigma > 310 km/s, subject to a correction for the unknown disc inclination. This result implies that this source is consistent with the local M--sigma relation, or offset at most by an order of magnitude in black hole mass. In contrast, the assumption of a bulge origin for the [C II] emission line would lead to a conclusion that the black hole is nearly two orders of magnitude more massive than predicted by the M--sigma relation, similar to previous findings for other high-redshift QSOs. As disc rotation may be a common origin for [C II] emission at high redshifts, these results stress that careful consideration of dynamical origins is required when using observations of this line to derive properties of high-redshift galaxies.
Observations revealed rich dynamics within prominences, the cool 10,000 K, macroscopic (sizes of order 100 Mm) "clouds" in the million degree solar corona. Even quiescent prominences are continuously perturbed by hot, rising bubbles. Since prominence matter is hundredfold denser than coronal plasma, this bubbling is related to Rayleigh-Taylor instabilities. Here we report on true macroscopic simulations well into this bubbling phase, adopting a magnetohydrodynamic description from chromospheric layers up to 30 Mm height. Our virtual prominences rapidly establish fully non-linear (magneto)convective motions where hot bubbles interplay with falling pillars, with dynamical details including upwelling pillars forming within bubbles. Our simulations show impacting Rayleigh-Taylor fingers reflecting on transition region plasma, ensuring that cool, dense chromospheric material gets mixed with prominence matter up to very large heights. This offers an explanation for the return mass cycle mystery for prominence material. Synthetic views at extreme ultraviolet wavelengths show remarkable agreement with observations, with clear indications of shear-flow induced fragmentations.
We investigate the global cold dust properties of 85 nearby (z < 0.5) QSOs, chosen from the Palomar-Green sample of optically luminous quasars. We determine their infrared spectral energy distributions and estimate their rest-frame luminosities by combining Herschel data from 70 to 500 microns with near-infrared and mid-infrared measurements from the Two Micron All Sky Survey (2MASS) and the Wide-Field Infrared Survey Explorer (WISE). In most sources the far-infrared (FIR) emission can be attributed to thermally heated dust. Single temperature modified black body fits to the FIR photometry give an average dust temperature for the sample of 33~K, with a standard deviation of 8~K, and an average dust mass of 7E6 Solar Masses with a standard deviation of 9E6 Solar Masses. Estimates of star-formation that are based on the FIR continuum emission correlate with those based on the 11.3 microns PAH feature, however, the star-formation rates estimated from the FIR continuum are higher than those estimated from the 11.3 microns PAH emission. We attribute this result to a variety of factors including the possible destruction of the PAHs and that, in some sources, a fraction of the FIR originates from dust heated by the active galactic nucleus and by old stars.
Optical UBVRI photometric measurements using the Faulkes Telescope North were taken in early 2011 and combined with 2MASS JHK$_s$ and WISE infrared photometry as well as UCAC4 proper motion data in order to estimate the main parameters of the galactic open cluster NGC 2215 of which large uncertainty exists in the current literature. Fitting a King model we estimate a core radius of 1.12$'\pm$0.04$'$ (0.24$\pm$0.01pc) and a limiting radius of $4.3'\pm$0.5$'$ (0.94$\pm$0.11pc) for the cluster. The results of isochrone fits indicates an age of $log(t)=8.85\pm0.10$ with a distance of $d=790\pm90$pc, a metallicity of $[Fe/H]=-0.40\pm0.10$ dex and a reddening of $E(B-V)=0.26\pm0.04$. A proportion of the work in this study was undertaken by Australian and Canadian upper secondary school students involved in the Space to Grow astronomy education project, and is the first scientific publication to have utilized our star cluster photometry curriculum materials.
Solar flares are energetic events taking place in the Sun's atmosphere, and their effects can greatly impact the environment of the surrounding planets. In particular, eruptive flares, as opposed to confined flares, launch coronal mass ejections into the interplanetary medium, and as such, are one of the main drivers of space weather. After briefly reviewing the main characteristics of solar flares, we summarize the processes that can account for the build up and release of energy during their evolution. In particular, we focus on the development of recent 3D numerical simulations that explain many of the observed flare features. These simulations can also provide predictions of the dynamical evolution of coronal and photospheric magnetic field. Here we present a few observational examples that, together with numerical modelling, point to the underlying physical mechanisms of the eruptions.
In a hydrodynamic Taylor-Couette system a rotation law with positive shear ('super-rotation') is linearly stable for all Reynolds numbers. It is also known that a conducting fluid under the presence of a sufficiently strong axial electric current becomes unstable against nonaxisymmetric disturbances. It is thus suggestive that a super-rotation law may stabilize the rotating pinch. But for magnetic Prandtl number Pm $\neq 1$ and for small magnetic Mach numbers of rotation also super-rotation supports the instability. For steeper and steeper rotation profiles the critical Hartmann numbers converge to a finite minimum value which for Pm $\gg 1$ or Pm $\ll 1$ looses its dependence on Pm. For super-rotation and for rigid rotation the sign of the azimuthal drift of the nonaxisymmetric hydromagnetic instability pattern strongly depends on the magnetic Prandtl number. The pattern corotates with the flow for Pm $\geq 1$ and it counterrotates for Pm $\ll 1$ so that a critical Pm exists (between 0.1 and 1) with solutions even resting in the laboratory system. On the other hand, for sub-rotation the instability pattern for all Pm migrates in the direction of the basic rotation. -- An electric current of (only) 3.6 kAmp suffices to realize the subcritical excitation for super-rotation in the laboratory using liquid sodium as the conducting fluid between the rotating cylinders.
Measurements of explosive nucleosynthesis yields in core-collapse supernovae provide tests for explosion models. We investigate constraints on explosive conditions derivable from measured amounts of nickel and iron after radioactive decays using nucleosynthesis networks with parameterized thermodynamic trajectories. The Ni/Fe ratio is for most regimes dominated by the production ratio of 58Ni/(54Fe + 56Ni), which tends to grow with higher neutron excess and with higher entropy. For SN 2012ec, a supernova that produced a Ni/Fe ratio of $3.4\pm1.2$ times solar, we find that burning of a fuel with neutron excess $\eta \approx 6\times 10^{-3}$ is required. Unless the progenitor metallicity is over 5 times solar, the only layer in the progenitor with such a neutron excess is the silicon shell. Supernovae producing large amounts of stable nickel thus suggest that this deep-lying layer can be, at least partially, ejected in the explosion. We find that common spherically symmetric models of $M_{\rm ZAMS} \lesssim 13$ Msun stars exploding with a delay time of less than one second ($M_{\rm cut} < 1.5$ Msun) are able to achieve such silicon-shell ejection. Supernovae that produce solar or sub-solar Ni/Fe ratios, such as SN 1987A, must instead have burnt and ejected only oxygen-shell material, which allows a lower limit to the mass cut to be set. Finally, we find that the extreme Ni/Fe value of 60-75 times solar derived for the Crab cannot be reproduced by any realistic-entropy burning outside the iron core, and neutrino-neutronization obtained in electron-capture models remains the only viable explanation.
The study of dynamical processes in protoplanetary disks is essential to understand planet formation. In this context, transition disks are prime targets because they are at an advanced stage of disk clearing and may harbor direct signatures of disk evolution. In this paper, we aim to derive new constraints on the structure of the transition disk MWC 758, to detect non-axisymmetric features and understand their origin. We obtained infrared polarized intensity observations of the protoplanetary disk MWC 758 with SPHERE/VLT at 1.04 microns to resolve scattered light at a smaller inner working angle (0.093") and a higher angular resolution (0.027") than previously achieved. We observe polarized scattered light within 0.53" (148 au) down to the inner working angle (26 au) and detect distinct non-axisymmetric features but no fully depleted cavity. The two small-scale spiral features that were previously detected with HiCIAO are resolved more clearly, and new features are identified, including two that are located at previously inaccessible radii close to the star. We present a model based on the spiral density wave theory with two planetary companions in circular orbits. The best model requires a high disk aspect ratio (H/r~0.20 at the planet locations) to account for the large pitch angles which implies a very warm disk. Our observations reveal the complex morphology of the disk MWC758. To understand the origin of the detected features, the combination of high-resolution observations in the submillimeter with ALMA and detailed modeling is needed.
The observation of thermal emission from isolated neutron stars and the modeling of the corresponding cooling curves has been very useful to get information on the properties of matter at very high densities. More recently, the detection of quiescent thermal emission from neutron stars in low mass X-ray binary systems after active periods opened a new window to the physics of matter at lower densities. Here we analyze a few sources that have been recently monitored and we show how the models can be used to establish constraints on the crust composition and their transport properties, depending on the astrophysical scenarios assumed.
We present numerical simulations in 3D settings where coronal rain phenomena take place in a magnetic configuration of a quadrupolar arcade system. Our simulation is a magnetohydrodynamic simulation including anisotropic thermal conduction, optically thin radiative losses, and parametrised heating as main thermodynamical features to construct a realistic arcade configuration from chromospheric to coronal heights. The plasma evaporation from chromospheric and transition region heights eventually causes localised runaway condensation events and we witness the formation of plasma blobs due to thermal instability, that evolve dynamically in the heated arcade part and move gradually downwards due to interchange type dynamics. Unlike earlier 2.5D simulations, in this case there is no large scale prominence formation observed, but a continuous coronal rain develops which shows clear indications of Rayleigh-Taylor or interchange instability, that causes the denser plasma located above the transition region to fall down, as the system moves towards a more stable state. Linear stability analysis is used in the non-linear regime for gaining insight and giving a prediction of the system's evolution. After the plasma blobs descend through interchange, they follow the magnetic field topology more closely in the lower coronal regions, where they are guided by the magnetic dips.
Observed galaxy clustering exhibits local transverse statistical isotropy around the line-of-sight (LOS). The variation of the LOS across a galaxy survey complicates the measurement of the observed clustering as a function of the angle to the LOS, as Fast Fourier Transforms (FFTs) based on cartesian grids, cannot individually allow for this. Recent advances in methodology for calculating LOS-dependent clustering in Fourier space include the realisation that power spectrum LOS-dependent moments can be constructed from sums over galaxies, based on approximating the LOS to each pair of galaxies by the LOS to one of them. We show that we can implement this method using multiple FFTs, each measuring the LOS-weighted clustering along different axes. The N log(N) nature of FFTs means that the computational speed-up is a factor of >1000 compared with summing over galaxies. This development should be beneficial for future projects such as DESI and Euclid which will provide an order of magnitude more galaxies than current surveys.
We investigate the higher-order correlation properties of the VIMOS Public Extragalactic Redshift Survey (VIPERS) to test the hierarchical scaling hypothesis at z~1 and the dependence on galaxy luminosity, stellar mass, and redshift. We also aim to assess deviations from the linearity of galaxy bias independently from a previously performed analysis of our survey (Di Porto et al. 2014). We have measured the count probability distribution function in cells of radii 3 < R < 10 Mpc/h, deriving $\sigma_{8g}$, the volume-averaged two-,three-,and four-point correlation functions and the normalized skewness $S_{3g}$ and kurtosis $S_{4g}$ for volume-limited subsamples covering the ranges $-19.5 \le M_B(z=1.1)-5log(h) \le -21.0$, $9.0 < log(M*/M_{\odot} h^{-2}) \le 11.0$, $0.5 \le z < 1.1$. We have thus performed the first measurement of high-order correlations at z~1 in a spectroscopic redshift survey. Our main results are the following. 1) The hierarchical scaling holds throughout the whole range of scale and z. 2) We do not find a significant dependence of $S_{3g}$ on luminosity (below z=0.9 $S_{3g}$ decreases with luminosity but only at 1{\sigma}-level). 3) We do not detect a significant dependence of $S_{3g}$ and $S_{4g}$ on scale, except beyond z~0.9, where the dependence can be explained as a consequence of sample variance. 4) We do not detect an evolution of $S_{3g}$ and $S_{4g}$ with z. 5) The linear bias factor $b=\sigma_{8g}/\sigma_{8m}$ increases with z, in agreement with previous results. 6) We quantify deviations from the linear bias by means of the Taylor expansion parameter $b_2$. Our results are compatible with a null non-linear bias term, but taking into account other available data we argue that there is evidence for a small non-linear bias term.
As hundreds of gas giant planets have been discovered, we study how these planets form and evolve in different stellar environments, specifically in multiple stellar systems. In such systems, stellar companions may have a profound influence on gas giant planet formation and evolution via several dynamical effects such as truncation and perturbation. We select 84 Kepler Objects of Interest (KOIs) with gas giant planet candidates. We obtain high-angular resolution images using telescopes with adaptive optics (AO) systems. Together with the AO data, we use archival radial velocity data and dynamical analysis to constrain the presence of stellar companions. We detect 59 stellar companions around 40 KOIs for which we develop methods of testing their physical association. These methods are based on color information and galactic stellar population statistics. We find evidence of suppressive planet formation within 20 AU by comparing stellar multiplicity. The stellar multiplicity rate for planet host stars is 0$^{+5}_{-0}$\% within 20 AU. In comparison, the stellar multiplicity rate is 18\%$\pm$2\% for the control sample, i.e., field stars in the solar neighborhood. The stellar multiplicity rate for planet host stars is 34\%$\pm$8\% for separations between 20 and 200 AU, which is higher than the control sample at 12\%$\pm$2\%. Beyond 200 AU, stellar multiplicity rates are comparable between planet host stars and the control sample. We discuss the implications of the results to gas giant planet formation and evolution.
An optical light curve of SU UMa type dwarf nova V1504 Cyg taken by Kepler was analysed in order to study fast optical variability (flickering). We calculated power density spectra and rms-flux relations for two different stages of activity, i.e. quiescence and regular outbursts. A multicomponent power density spectrum with two break frequencies was found during both activity stages. The rms-flux relation is obvious only in the quiescent data. However, while the collection of all outburst data do not show this variability, every individual outburst does show it in the majority of cases keeping the rms value approximately in the same interval. Furthermore, the same analysis was performed for light curve subsamples taken from the beginning, middle and the end of the supercycle both for quiescence and regular outbursts. Every light curve subsample shows the same multicomponent power density spectrum. The stability of the break frequencies over the supercycle can be confirmed for all frequencies except for the high break frequency during outburst, which shows variability, but with rather low confidence. Finally, the low break frequency can be associated with the geometrically thin disc or its inner edge, while the high break frequency can originate from the inner geometrically thick hot disc. Furthermore, with our statistical method to simulate flickering light curves, we show that the outburst flickering light curve of V1504 Cyg needs an additional constant flux level to explain the observed rms-flux behaviour. Therefore, during the outbursts another non-turbulent radiation source should be present.
A model of a supernova explosion inside a dense extended hydrogenless envelope is proposed to explain the properties of the light curve for one of the superluminous supernovae PTF12dam. It is argued in the literature that the flux of this supernova rises too fast to be explained by the explosion model due to the instability associated with the electron-positron pair production (pair-instability supernova, PISNe), but it is well described by the models with energy input by a magnetar. We show that the PTF12dam-type supernovae can be explained without a magnetar in a model with a radiative shock in a dense circumstellar envelope that does not require an excessively large explosion energy.
We present results from Washington CT1 photometry for eleven star fields located in the western outskirts of the Small Magellanic Cloud (SMC), which cover angular distances to its centre from 2 up to 13 degrees (~ 2.2 - 13.8 kpc). The colour- magnitude diagrams, cleaned from the unavoidable Milky Way (MW) and background galaxy signatures, reveal that the most distant dominant main sequence (MS) stellar populations from the SMC centre are located at an angular distance of ~ 5.7 deg (6.1 kpc); no sign of farther clear SMC MS is visible other than the residuals from the MW/background field contamination. The derived ages and metallicities for the dominant stellar populations of the western SMC periphery show a constant metallicity level ([Fe/H] = -1.0 dex) and an approximately constant age value (~ 7-8 Gyr). Their age-metallicity relationship (AMR) do not clearly differ from the most comprehensive AMRs derived for almost the entire SMC main body. Finally, the range of ages of the dominant stellar populations in the western SMC periphery confirms that the major stellar mass formation activity at the very early galaxy epoch peaked ~ 7-8 Gyr ago.
This paper deals with the application of the creep tide theory (Ferraz-Mello, CeMDA 116, 109, 2013) to the rotation of close-in satellites, Mercury, close-in exoplanets and their host stars. The solutions show two extreme cases: close-in giant gaseous planets, with fast relaxation (low viscosity) and satellites and Earth-like planets, with slow relaxation (high viscosity). The rotation of close-in gaseous planets follows the classical Darwinian pattern: it is tidally driven towards a stationary solution which is synchronized, but, if the orbit is elliptical, with a frequency larger than the orbital mean-motion. The rotation of rocky bodies, however, may be driven to several attractors whose frequencies are 1/2,1,3/2,2,5/2 ... times the mean-motion. The number of attractors increases with the viscosity of the body and with the orbital eccentricity. The classical example is Mercury, whose rotational period is 2/3 of the orbital period (3/2 attractor). The planet behaves as a molten body with a relaxation that allowed it to cross the 2/1 attractor without being trapped, but not to escape being trapped in the 3/2 one. In that case, the relaxation is estimated to lie in the interval 4.6 -- 27 x 10^{-9} s^{-1} (equivalent to a quality factor roughly constrained to the interval 5<Q<50). The stars have relaxation similar to the hot Jupiters and their rotation is also driven to the only stationary solution existing in these cases. However, solar-type stars may lose angular momentum due to stellar wind, braking the rotation and displacing the attractor towards larger periods. Old active host stars with big close-in companions generally have rotational periods larger than the orbital periods of the companions. The paper also includes the study of the energy dissipation and the evolution of the orbital eccentricity.
The variation of remotely sensed neutron count rates is measured as a function of cratercentric distance using data from the Lunar Prospector Neutron Spectrometer. The count rate, stacked over many craters, peaks over the crater centre, has a minimum near the crater rim and at larger distances it increases to a mean value that is up to 1% lower than the mean count rate observed over the crater. A simple model is presented, based upon an analytical topographical profile for the stacked craters fitted to data from the Lunar Orbiter Laser Altimeter (LOLA). The effect of topography coupled with neutron beaming from the surface largely reproduces the observed count rate profiles. However, a model that better fits the observations can be found by including the additional freedom to increase the neutron emissivity of the crater area by ~0.35% relative to the unperturbed surface. It is unclear what might give rise to this effect, but it may relate to additional surface roughness in the vicinities of craters. The amplitude of the crater-related signal in the neutron count rate is small, but not too small to demand consideration when inferring water-equivalent hydrogen (WEH) weight percentages in polar permanently shaded regions (PSRs). If the crater-wide count rate excess is levered into a much smaller PSR, then it can lead to a significantly biased inferred WEH weight percentage. For instance, it may increase the inferred WEH for Cabeus crater at the Moon's South Pole from ~1% to ~4%.
Motivated by the discovery of prolate rotation of stars in Andromeda II, a dwarf spheroidal companion of M31, we study the origin of this type of streaming motion via mergers of disky dwarf galaxies. We simulate merger events between two identical dwarfs changing the initial inclination of their disks with respect to the orbit and the amount of orbital angular momentum. On radial orbits the amount of prolate rotation in the merger remnants correlates strongly with the inclination of the disks and is well understood as due to the conservation of the angular momentum component of the disks along the merger axis. For non-radial orbits prolate rotation may still be produced if the orbital angular momentum is initially not much larger than the intrinsic angular momentum of the disks. The orbital structure of the remnants with significant rotation is dominated by box orbits in the center and long-axis tubes in the outer parts. We also detect significant figure rotation resulting from the tidal distortion of the disks before the merger. The frequency analysis of stellar orbits in the plane perpendicular to the major axis reveals the presence of two families roughly corresponding to inner and outer long-axis tubes. The fraction of inner tubes is largest in the remnant forming from disks oriented most vertically initially and is responsible for the boxy shape of the galaxy. We conclude that prolate rotation may result from mergers with a variety of initial conditions and no fine tuning is necessary to reproduce this feature.
We present a kinematic analysis of the globular cluster systems and diffuse stellar light of four intermediate luminosity (sub-$L^{\ast}$) early-type galaxies in the Virgo cluster based on Gemini/GMOS data. Our galaxy sample is fainter ($-23.8<M_K<-22.7$) than most previous studies, nearly doubling the number of galaxies in this magnitude range that now have GC kinematics. The data for the diffuse light extends to $4R_e$, and the data for the globular clusters reaches 8--$12R_e$. We find that the kinematics in these outer regions are all different despite the fact that these four galaxies have similar photometric properties, and are uniformly classified as "fast rotators" from their stellar kinematics within $1R_e$. The globular cluster systems exhibit a wide range of kinematic morphology. The rotation axis and amplitude can change between the inner and outer regions, including a case of counter-rotation. This difference shows the importance of wide-field kinematic studies, and shows that stellar and GC kinematics can change significantly as one moves beyond the inner regions of galaxies. Moreover, the kinematics of the globular cluster systems can differ from that of the stars, suggesting that the formation of the two populations are also distinct.
Observations on 2011 August 9 of an X6.9-class flare in active region (AR) 11263 by the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO), were followed by a rare detection of vertical kink oscillations in a large-scale coronal active region plasma curtain in EUV coronal lines. The damped oscillations with periods in the range 8.8-14.9 min were detected and analyzed recently. Our aim is to study the generation and propagation of the MHD oscillations in the plasma curtain taking into account realistic 3D magnetic and density structure of the curtain. We also aim at testing and improving coronal seismology for more accurate determination of the magnetic field than with standard method. We use the observed morphological and dynamical conditions, as well as plasma properties of the coronal curtain based on Differential Emission Measure (DEM) analysis to initialize a 3D MHD model of its vertical and transverse oscillations by implementing the impulsively excited velocity pulse mimicking the flare generated nonlinear fast magnetosonic propagating disturbance interacting with the curtain obliquely. The model is simplified by utilizing initial dipole magnetic field, isothermal energy equation, and gravitationally stratified density guided by observational parameters. Using the 3D MHD model, we are able to reproduce the details of the vertical oscillations and study the process of their excitation by nonlinear fast magnetosonic pulse, propagation, and damping, finding agreement with the observations. We estimate the accuracy of simplified slab-based coronal seismology by comparing the determined magnetic field strength to actual values from the 3D MHD modeling results and demonstrate the importance of taking into account more realistic magnetic geometry and density for improving coronal seismology.
Atmospheric optical turbulence seriously limits the performance of high angular resolution instruments. An 8-night campaign of measurements was carried out at the LAMOST site in 2011, to characterize the optical turbulence. Two instruments were set up during the campaign: a Differential Image Motion Monitor (DIMM) used to measure the total atmospheric seeing, and a Single Star Scidar (SSS) to measure the vertical profiles of the turbulence C_n^2(h) and the horizontal wind velocity V(h). The optical turbulence parameters are also calculated with the Weather Research and Forecasting (WRF) model coupled with the Trinquet-Vernin model, which describes optical effects of atmospheric turbulence by using the local meteorological parameters. This paper presents assessment of the optical parameters involved in high angular resolution astronomy. Its includes seeing, isoplanatic angle, coherence time, coherence etendue, vertical profiles of optical turbulence intensity _n^2(h)$ and horizontal wind speed V(h). The median seeing is respectively 1.01 arcsec, 1.17 arcsec and 1.07arcsec as measured with the DIMM, the SSS and predicted with WRF model. The history of seeing measurements at the LAMOST site are reviewed, and the turbulence measurements in this campaign are compared with other astronomical observatories in the world.
Seismic observations by the space-borne mission \emph{Kepler} have shown that
the core of red giant stars slows down while evolving, requiring an efficient
physical mechanism to extract angular momentum from the inner layers. Current
stellar evolution codes fail to reproduce the observed rotation rates by
several orders of magnitude, and predict a drastic spin-up of red giant cores
instead. New efficient mechanisms of angular momentum transport are thus
required.
In this framework, our aim is to investigate the possibility that mixed modes
extract angular momentum from the inner radiative regions of evolved low-mass
stars. To this end, we consider the Transformed Eulerian Mean (TEM) formalism,
introduced by Andrews \& McIntyre (1978), that allows us to consider the
combined effect of both the wave momentum flux in the mean angular momentum
equation and the wave heat flux in the mean entropy equation as well as their
interplay with the meridional circulation.
In radiative layers of evolved low-mass stars, the quasi-adiabatic
approximation, the limit of slow rotation, and the asymptotic regime can be
applied for mixed modes and enable us to establish a prescription for the wave
fluxes in the mean equations. The formalism is finally applied to a $1.3
M_\odot$ benchmark model, representative of observed CoRoT and \emph{Kepler}
oscillating evolved stars.
We show that the influence of the wave heat flux on the mean angular momentum
is not negligible and that the overall effect of mixed modes is to extract
angular momentum from the innermost region of the star. A quantitative and
accurate estimate requires realistic values of mode amplitudes. This is
provided in a companion paper.
We systematically reanalyze two previous observations of the black hole (BH) GX 339-4 in the very high and intermediate state taken with $\emph{XMM-Newton}$ and $\emph{Suzaku}$. We utilize up-to-date data reduction procedures and implement the recently developed, self-consistent model for X-ray reflection and relativistic ray tracing, {\sc relxill}. In the very high and intermediate state, the rate of accretion is high and thus the disk remains close to the innermost stable circular orbit (ISCO). We require a common spin parameter and inclination when fitting the two observations since these parameters should remain constant across all states. This allows for the most accurate determination of the spin parameter of this galactic black hole binary from fitting the Fe K$\alpha$ emission line and provides a chance to test previous estimates. We find GX 339-4 to be consistent with a near maximally spinning black hole with a spin parameter $a_{*}$ $>0.97$ with an inclination of $36 \pm 4$ degrees. This spin value is consistent with previous high estimates for this object. Further, if the inner disk is aligned with the binary inclination, this modest inclination returns a high black hole mass, but they need not be aligned. Additionally, we explore how the spin is correlated with the power of the jet emitted but find no correlation between the two.
The detection of mixed modes in subgiants and red giants by the CoRoT and
\emph{Kepler} space-borne missions allows us to investigate the internal
structure of evolved low-mass stars. In particular, the measurement of the mean
core rotation rate as a function of the evolution places stringent constraints
on the physical mechanisms responsible for the angular momentum redistribution
in stars. It showed that the current stellar evolution codes including the
modelling of rotation fail to reproduce the observations. An additional
physical process that efficiently extracts angular momentum from the core is
thus necessary.
Our aim is to assess the ability of mixed modes to do this. To this end, we
developed a formalism that provides a modelling of the wave fluxes in both the
mean angular momentum and the mean energy equations in a companion paper. In
this article, mode amplitudes are modelled based on recent asteroseismic
observations, and a quantitative estimate of the angular momentum transfer is
obtained. This is performed for a benchmark model of 1.3 $M_{\odot}$ at three
evolutionary stages, representative of the evolved pulsating stars observed by
CoRoT and Kepler.
We show that mixed modes extract angular momentum from the innermost regions
of subgiants and red giants. However, this transport of angular momentum from
the core is unlikely to counterbalance the effect of the core contraction in
subgiants and early red giants. In contrast, for more evolved red giants, mixed
modes are found efficient enough to balance and exceed the effect of the core
contraction, in particular in the hydrogen-burning shell. Our results thus
indicate that mixed modes are a promising candidate to explain the observed
spin-down of the core of evolved red giants, but that an other mechanism is to
be invoked for subgiants and early red giants.
The Central Molecular Zone (CMZ) of the Milky Way shows several peculiar properties: a large star formation rate, some of the most massive young star clusters and molecular clouds in the Galaxy, and a twisted ring morphology in molecular gas. In this paper, I use SPH simulations to show that most of these properties can be explained as due to a recent outburst of AGN activity in Sgr A*, the central supermassive black hole of the Milky Way. In particular, the narrow ring of dense gas, massive gas clouds, young star clusters and an elevated SFR can all be caused by the passage of an AGN outflow through the system, which compresses the gas and triggers fragmentation. Furthermore, I show that the asymmetric distribution of gas, as observed in the CMZ, can be produced by outflow-induced instabilities from an initially axisymmetric gas disc. Angular momentum mixing in the disc produces some low angular momentum material, which can subsequently feed Sgr A*. These processes can occur in any galaxy that experiences an AGN episode, leading to bursts of nuclear star formation much stronger than pure bar-driven mass inflows would predict.
We use the "Evolution and Assembly of GaLaxies and their Environments" ( EAGLE ) suite of hydrodynamical cosmological simulations to measure offsets between the centres of stellar and dark matter components of galaxies. We find that the vast majority (>95%) of the simulated galaxies display an offset smaller than the gravitational softening length of the simulations ($\epsilon = 700$ pc), both for field galaxies and satellites in clusters and groups. We also find no systematic trailing or leading of the dark matter along a galaxy's direction of motion. The offsets are consistent with being randomly drawn from a Maxwellian distribution with $\sigma = 196$ pc. Since astrophysical effects produce no feasible analogues for the $1.62^{+0.47}_{-0.49}$ kpc offset recently observed in Abell 3827, this observational result is in tension with the collisionless cold dark matter model assumed in the simulations.
The centre of our Galaxy is one of the most studied and yet enigmatic places in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre (GC) is the ideal environment to study the extreme processes that take place in the vicinity of a supermassive black hole (SMBH). Despite the hostile environment, several tens of early-type stars populate the central parsec of our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The formation of such early-type stars has been a puzzle for a long time: molecular clouds should be tidally disrupted by the SMBH before they can fragment into stars. We review the main scenarios proposed to explain the formation and the dynamical evolution of the early-type stars in the GC. In particular, we discuss the most popular in situ scenarios (accretion disc fragmentation and molecular cloud disruption) and migration scenarios (star cluster inspiral and Hills mechanism). We focus on the most pressing challenges that must be faced to shed light on the process of star formation in the vicinity of a SMBH.
A binary supermassive black hole loses energy via ejection of stars in a galactic nucleus, until emission of gravitational waves becomes strong enough to induce rapid coalescence. Evolution via the gravitational slingshot requires that stars be continuously supplied to the binary, and it is known that in spherical galaxies the reservoir of such stars is quickly depleted, leading to stalling of the binary at parsec-scale separations. Recent N-body simulations of galaxy mergers and isolated nonspherical galaxies suggest that this stalling may not occur in less idealized systems. However, it remains unclear to what degree these conclusions are affected by collisional relaxation, which is much stronger in the numerical simulations than in real galaxies. In this study, we present a novel Monte Carlo method that can efficiently deal with both collisional and collisionless dynamics, and with galaxy models having arbitrary shapes. We show that without relaxation, the final-parsec problem may be overcome only in triaxial galaxies. Axisymmetry is not enough, but even a moderate departure from axisymmetry is sufficient to keep the binary shrinking. We find that the binary hardening rate is always substantially lower than the maximum possible, "full-loss-cone" rate, and that it decreases with time, but that stellar-dynamical interactions are nevertheless able to drive the binary to coalescence on a timescale <=1 Gyr in any triaxial galaxy.
High-mass X-ray binaries (HMXBs) might have contributed a non-negligible fraction of the energy feedback to the interstellar and intergalactic media at high redshift, becoming important sources for the heating and ionization history of the Universe. However, the importance of this contribution depends on the hypothesized increase in the number of HMXBs formed in low-metallicity galaxies and in their luminosities. In this work we test the aforementioned hypothesis, and quantify the metallicity dependence of HMXB population properties. We compile from the literature a large set of data on the sizes and X-ray luminosities of HMXB populations in nearby galaxies with known metallicities and star formation rates. We use Bayesian inference to fit simple Monte Carlo models that describe the metallicity dependence of the size and luminosity of the HMXB populations. We find that HMXBs are typically ten times more numerous per unit star formation rate in low-metallicity galaxies (12 + log(O/H) < 8, namely < 20% solar) than in solar-metallicity galaxies. The metallicity dependence of the luminosity of HMXBs is small compared to that of the population size. Our results support the hypothesis that HMXBs are more numerous in low-metallicity galaxies, implying the need to investigate the feedback in the form of X-rays and energetic mass outflows of these high-energy sources during cosmic dawn.
We report the multi-wavelength identification of the X-ray sources found in the Subaru-XMM-Newton Deep Survey (SXDS) using deep imaging data covering the wavelength range between the far-UV to the mid-IR. We select a primary counterpart of each X-ray source by applying the likelihood ratio method to R-band, 3.6micron, near-UV, and 24micron source catalogs as well as matching catalogs of AGN candidates selected in 1.4GHz radio and i'-band variability surveys. Once candidates of Galactic stars, ultra-luminous X-ray sources in a nearby galaxy, and clusters of galaxies are removed there are 896 AGN candidates in the sample. We conduct spectroscopic observations of the primary counterparts with multi-object spectrographs in the optical and NIR; 65\% of the X-ray AGN candidates are spectroscopically-identified. For the remaining X-ray AGN candidates, we evaluate their photometric redshift with photometric data in 15 bands. Utilising the multi-wavelength photometric data of the large sample of X-ray selected AGNs, we evaluate the stellar masses, M*, of the host galaxies of the narrow-line AGNs. The distribution of the stellar mass is remarkably constant from z=0.1 to 4.0. The relation between M* and 2--10 keV luminosity can be explained with strong cosmological evolution of the relationship between the black hole mass and M*. We also evaluate the scatter of the UV-MIR spectral energy distribution (SED) of the X-ray AGNs as a function of X-ray luminosity and absorption to the nucleus. The scatter is compared with galaxies which have redshift and stellar mass distribution matched with the X-ray AGN. The UV-NIR SEDs of obscured X-ray AGNs are similar to those of the galaxies in the matched sample. In the NIR-MIR range, the median SEDs of X-ray AGNs are redder, but the scatter of the SEDs of the X-ray AGN broadly overlaps that of the galaxies in the matched sample.
Accurate photometric redshift are a lynchpin for many future experiments to pin down the cosmological model and for studies of galaxy evolution. In this study, a novel sparse regression framework for photometric redshift estimation is presented. Data from a simulated survey was used to train and test the proposed models. We show that approaches which include careful data preparation and model design offer a significant improvement in comparison with several competing machine learning algorithms. Standard implementation of most regression algorithms has as the objective the minimization of the sum of squared errors. For redshift inference, however, this induces a bias in the posterior mean of the output distribution, which can be problematic. In this paper we optimize to directly target minimizing $\Delta z = (z_\textrm{s} - z_\textrm{p})/(1+z_\textrm{s})$ and address the bias problem via a distribution-based weighting scheme, incorporated as part of the optimization objective. The results are compared with other machine learning algorithms in the field such as Artificial Neural Networks (ANN), Gaussian Processes (GPs) and sparse GPs. The proposed framework reaches a mean absolute $\Delta z = 0.002(1+z_\textrm{s})$, with a maximum absolute error of 0.0432, over the redshift range of $0.2 \le z_\textrm{s} \le 2$, a factor of three improvement over standard ANNs used in the literature. We also investigate how the relative size of the training affects the photometric redshift accuracy. We find that a training set of $>$30 per cent of total sample size, provides little additional constraint on the photometric redshifts, and note that our GP formalism strongly outperforms ANN in the sparse data regime.
We study low frequency waves that propagate in a region of layered semi-convection. Layered semi-convection is predicted to be present in stellar and planetary interiors and can significantly modify the rate of thermal and compositional mixing. We derive a series of analytical dispersion relations for plane-parallel layered semi-convection in the Boussinesq approximation using a matrix transfer formalism. We find that like a continuously stratified medium, a semi-convective staircase -- in which small convective regions are separated by sharp density jumps -- supports internal gravity waves (g-modes). When the wavelength is much longer than the distance between semi-convective steps, these behave nearly like g-modes in a continuously stratified medium. However, the g-mode period spacing in a semi-convective region is systematically {\em smaller} than in a continuously stratified medium, and it decreases with decreasing mode frequency. When the g-mode wavelength becomes comparable to the distance between semi-convective steps, the g-mode frequencies deviate significantly from those of a continuously stratified medium (the frequencies are higher). G-modes with vertical wavelengths smaller than the distance between semi-convective steps are evanescent and do not propagate in the staircase. Thus, there is a lower cutoff frequency for a given horizontal wavenumber. We generalize our results to gravito-inertial waves relevant for rapidly rotating stars and planets. Finally, we assess the prospects for detecting layered semi-convection using astero/planetary seismology.
This paper calculates the expected gravitational wave background (GWB) in the quasi-steady state cosmology (QSSC). The principal sources of gravitational waves in the QSSC are the minicreation events (MCE). With suitable assumptions the GWB can be computed both numerically and with analytical methods. It is argued that the GWB in QSSC differs from that predicted for the standard cosmology and a future technology of detectors will be able to decide between the two predictions. We also derive a formula for the flux density of a typical extragalactic source of gravitational waves.
We investigate whether the anomalous elemental abundance patterns in some of the C-enhanced metal-poor-s+r (CEMP-r/s) stars are consistent with predictions of nucleosynthesis yields from the i-process, a neutron-capture regime at neutron densities intermediate between those typical for the slow (s) and rapid (r) processes. Conditions necessary for the i-process are expected to be met at multiple stellar sites, such as the He-core and He-shell flashes in low-metallicity low-mass stars, super-AGB and post-AGB stars, as well as low-metallicity massive stars. We have found that single-exposure one-zone simulations of the i-process reproduce the abundance patterns in some of the CEMP-r/s stars much better than the model that assumes a superposition of yields from s- and r-process sources. Our previous study of nuclear data uncertainties relevant to the i-process revealed that they could have a significant impact on the i-process yields obtained in our idealized one-zone calculations, leading, for example, to ~0.7dex uncertainty in our predicted [Ba/La] ratio. Recent 3D hydrodynamic simulations of convection driven by a He-shell flash in post-AGB Sakurai's object have discovered a new mode of non-radial instabilities: the Global Oscillation of Shell H-ingestion. This has demonstrated that spherically symmetric stellar evolution simulations cannot be used to accurately model physical conditions for the i-process.
We propose a new class of dark matter models with unusual phenomenology. What is ordinary about our models is that dark matter particles are WIMPs, they are weakly coupled to the Standard Model and have weak scale masses. What is unusual is that they come in multiplets of a new "dark" non-Abelian gauge group with milli-weak coupling. The massless dark gluons of this dark gauge group contribute to the energy density of the universe as a form of weakly self-interacting dark radiation. In this paper we explore the consequences of having i.) dark matter in multiplets ii.) self-interacting dark radiation and iii.) dark matter which is weakly coupled to dark radiation. We find that i.) dark matter cross sections are modified by multiplicity factors which have significant consequences for collider searches and indirect detection, ii.) dark gluons have thermal abundances which affect the CMB as dark radiation. Unlike additional massless neutrino species the dark gluons are interacting and have vanishing viscosity and iii.) the coupling of dark radiation to dark matter represents a new mechanism for damping the large scale structure power spectrum. A combination of additional radiation and slightly damped structure is interesting because it can remove tensions between global $\Lambda$CDM fits from the CMB and direct measurements of the Hubble expansion rate ($H_0$) and large scale structure ($\sigma_8$).
The Standard Model Higgs potential becomes unstable at large field values. After clarifying the issue of gauge dependence of the effective potential, we study the cosmological evolution of the Higgs field in presence of this instability throughout inflation, reheating and the present epoch. We conclude that anti-de Sitter patches in which the Higgs field lies at its true vacuum are lethal for our universe. From this result, we derive upper bounds on the Hubble constant during inflation, which depend on the reheating temperature and on the Higgs coupling to the scalar curvature or to the inflaton. Finally we study how a speculative link between Higgs meta-stability and consistence of quantum gravity leads to a sharp prediction for the Higgs and top masses, which is consistent with measured values.
Massive gravity theories have been developed as viable IR modifications of gravity motivated by dark energy and the problem of the cosmological constant. On the other hand, modified gravity and modified dark matter theories were developed with the aim of solving the problems of standard cold dark matter at galactic scales. Here we propose to adapt the framework of ghost-free massive bigravity theories to reformulate the problem of dark matter at galactic scales. We investigate a promising alternative to dark matter called dipolar dark matter (DDM) in which two different species of dark matter are separately coupled to the two metrics of bigravity and are linked together by an internal vector field. We show that this model successfully reproduces the phenomenology of dark matter at galactic scales (i.e. MOND) as a result of a mechanism of gravitational polarisation. The model is safe in the gravitational sector, but because the two types of dark matter interact through the vector field, a ghostly degree of freedom in the decoupling limit is reintroduced in the dark matter sector. Crucial questions to address in future work is whether the polarisation mechanism can be realized in absence of ghosts, and what are the cosmological implications of the model.
We discuss a new scenario for early cosmology when the inflationary de Sitter phase emerges dynamically. This genuine quantum effect occurs as a result of dynamics of the topologically nontrivial sectors in a strongly coupled QCD- like gauge theory in an expanding universe. We test these ideas by explicit computations in hyperbolic space $ \mathbb{H}^3_{\kappa}\times \mathbb{S}^1_{\kappa^{-1}}$. We argue that the key element for this idea to work is the presence of nontrivial holonomy computed along $\mathbb{S}^1_{\kappa^{-1}}$. The effect is non-local in nature, non-analytical in coupling constant and can not be described in terms of any local propagating degree of freedom such as scalar inflaton field $\Phi(x)$. We discuss some profound phenomenological consequences of this scenario for inflationary cosmology. We also suggest to test these ideas in a tabletop experiment by measuring some specific corrections to the Casimir pressure in the Maxwell theory formulated on a topologically nontrivial manifold.
SgrA$^*$ is the supermassive black hole candidate at the center of the Galaxy and an ideal laboratory to test general relativity. Following previous work by other authors, we use the Polish doughnut model to describe an optically thin and constant angular momentum ion torus in hydrodynamical equilibrium and model the accretion structure around SgrA$^*$. The radiation mechanisms are bremsstrahlung, synchrotron emission, and inverse Compton scattering. We compute the spectrum as seen by a distant observer in Kerr and non-Kerr spacetimes and we study how an accurate measurement can constrain possible deviations form the Kerr solution. When the parameters of the ion torus are fixed, the spectrum is not affected by the strong degeneracy between the spin and the deformation parameter. This is in contrast with other approaches based on the study of thin disks and it may suggest that, if properly understood and in presence of good data, the spectrum of the accretion flow of SgrA$^*$ may be a powerful tool to test the Kerr metric. However, if the parameters of the ion torus are unknown, the constraints are much weaker.
In the present paper the results obtained in the investigation of possible diurnal effects for low-energy single-hit scintillation events of DAMA/LIBRA-phase1 (1.04 ton $\times$ yr exposure) have been analysed in terms of an effect expected in case of Dark Matter (DM) candidates inducing nuclear recoils and having high cross-section with ordinary matter, which implies low DM local density in order to fulfill the DAMA/LIBRA DM annual modulation results. This effect is due to the different Earth depths crossed by those DM candidates during the sidereal day.
We study the hydrodynamic regime of chiral plasmas at high temperature. We find a new type of gapless collective excitation induced by chiral effects in an external magnetic field. This is a transverse wave and is present even in incompressible fluids, unlike the chiral magnetic and chiral vortical waves. The velocity is proportional to the coefficient of the gravitational anomaly. We briefly discuss possible relevance of this "chiral Alfv\'en wave" in physical systems.
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The Cheshire Cat is a relatively poor group of galaxies dominated by two luminous elliptical galaxies surrounded by at least four arcs from gravitationally lensed background galaxies that give the system a humorous appearance. Our combined optical/X-ray study of this system reveals that it is experiencing a line of sight merger between two groups with a roughly equal mass ratio with a relative velocity of ~1350 km/s. One group was most likely a low-mass fossil group, while the other group would have almost fit the classical definition of a fossil group. The collision manifests itself in a bimodal galaxy velocity distribution, an elevated central X-ray temperature and luminosity indicative of a shock, and gravitational arc centers that do not coincide with either large elliptical galaxy. One of the luminous elliptical galaxies has a double nucleus embedded off-center in the stellar halo. The luminous ellipticals should merge in less than a Gyr, after which observers will see a massive 1.2-1.5 x 10^14 solar mass fossil group with an M_r = -24.0 brightest group galaxy at its center. Thus, the Cheshire Cat offers us the first opportunity to study a fossil group progenitor. We discuss the limitations of the classical definition of a fossil group in terms of magnitude gaps between the member galaxies. We also suggest that if the merging of fossil (or near-fossil) groups is a common avenue for creating present-day fossil groups, the time lag between the final galactic merging of the system and the onset of cooling in the shock-heated core could account for the observed lack of well-developed cool cores in some fossil groups.
Model-independent methods in cosmology have become an essential tool in order to deal with an increasing number of theoretical alternatives for explaining the late-time acceleration of the Universe. In principle, this provides a way of testing the Cosmological Concordance (or $\Lambda$CDM) model under different assumptions and to rule out whole classes of competing theories. One such model-independent method is the so-called cosmographic approach, which relies only in the homogeneity and isotropy of the Universe on large scales. We show that this method suffers from many shortcomings, providing biased results depending on the auxiliary variable used in the series expansion and is unable to rule out models or adequately reconstruct theories with higher-order derivatives in either the gravitational or matter sector. Consequently, in its present form, this method seems unable to provide reliable or useful results for cosmological applications.
Using a cosmological N-body numerical simulation of the formation of a galaxy cluster- sized halo, we analyze the temporal evolution of its globular cluster population. We follow the dynamical evolution of 38 galactic dark matter halos orbiting in a galaxy cluster that at redshift z=0 has a virial mass of 1.71 * 10 ^14 Msol h^-1. In order to mimic both "blue" and "red" populations of globular clusters, for each galactic halo we select two different sets of particles at high redshift (z ~ 1), constrained by the condition that, at redshift z=0, their average radial density profiles are similar to the observed profiles. As expected, the general galaxy cluster tidal field removes a significant fraction of the globular cluster populations to feed the intracluster population. On average, halos lost approximately 16% and 29% of their initial red and blue globular cluster populations, respectively. Our results suggest that these fractions strongly depend on the orbital trajectory of the galactic halo, specifically on the number of orbits and on the minimum pericentric distance to the galaxy cluster center that the halo has had. At a given time, these fractions also depend on the current clustercentric distance, just as observations show that the specific frequencyof globular clusters S_N depends on their clustercentric distance.
Cosmic reionization holds the key to understand structure formation in the Universe, and can inform us about the properties of the first sources, as their star formation efficiency and escape fraction of ionizing photons. By combining the recent release of Planck electron scattering optical depth data with observations of high-redshift quasar absorption spectra, we obtain strong constraints on viable reionization histories. We show that inclusion of Planck data favors a reionization scenario with a single stellar population. The mean $x_{\rm HI}$ drops from $\sim0.9$ at $z=10.6$ to $\sim0.02$ at $z=5.8$ and reionization is completed around $5.8\lesssim z\lesssim9.3$ (2-$\sigma$), thus indicating a significant reduction in contributions to reionization from high redshift sources. We can put independent constraints on the escape fraction $f_{\rm esc}$ of ionizing photons by incorporating the high-redshift galaxy luminosity function data into our analysis. We find that $f_{\rm esc}$ increases moderately from $9\%$ to $20\%$ in the redshift range $z=6-9$. Such result is however consistent at 2-$\sigma$ confidence level with a non-evolving escape fraction.
We revisit the relation between magnetic-field strength ($B$) and gas density ($\rho$) for contracting interstellar clouds and fragments (or, cores), which is central in observationally determining the dynamical importance of magnetic fields in cloud evolution and star formation. Recently, it has been claimed that a relation $B \propto \rho^{2/3} $ is statistically preferred over $B \propto \rho^{1/2}$ in molecular clouds, when magnetic field detections and nondetections from Zeeman observations are combined. This finding has unique observational implications on cloud and core geometry: The relation $B \propto \rho^{2/3} $ can only be realized under spherical contraction. However, no indication of spherical geometry can be found for the objects used in the original statistical analysis of the $B-\rho$ relation. We trace the origin of the inconsistency to simplifying assumptions in the statistical model used to arrive at the $B\propto \rho^{2/3}$ conclusion and to an underestimate of observational uncertainties in the determination of cloud and core densities. We show that, when these restrictive assumptions are relaxed, $B \propto \rho^{1/2}$ is the preferred relation for the (self-gravitating) molecular-cloud data, as theoretically predicted four decades ago.
We consider decaying dark matter (DDM) as a resolution to the possible tension between cosmic microwave background (CMB) and weak lensing (WL) based determinations of the amplitude of matter fluctuations, $\sigma_8$. We perform N-body simulations in a model where dark matter decays into dark radiation and develop an accurate fitting formula for the non-linear matter power spectrum, which enables us to test the DDM model by the combined measurements of CMB, WL and the baryon acoustic oscillation (BAO). We employ a Markov chain Monte Carlo analysis to examine the overlap of posterior distributions of the cosmological parameters, comparing CMB alone with WL+BAO. We find an overlap that is significantly larger in the DDM model than in the standard CDM model. This may be hinting at DDM, although current data is not constraining enough to unambiguously favour a non-zero dark matter decay rate $\Gamma$. From the combined CMB+WL data, we obtain a lower bound $\Gamma^{-1}\ge 97$ Gyr at 95 % C.L, which is less tight than the constraint from CMB alone.
The very existence of a dozen of high-redshift (z>4) blazars indicates that a much larger population of misaligned powerful jetted AGN was already in place when the Universe was <1.5 Gyr old. Such parent population proved to be very elusive, and escaped direct detection in radio surveys so far. High redshift blazars themselves seem to be failing in producing extended radio-lobes, raising questions about the connection between such class and the vaster population of radio-galaxies. We show that the interaction of the jet electrons with the intense cosmic microwave background (CMB) radiation explains the lack of extended radio emission in high redshift blazars and in their parent population, possibly accounting for the apparently missing misaligned counterparts of high redshift blazars. We then model the spectral energy distribution of blazar lobes following simple prescriptions, finding that most of them should be detectable by low frequency deep radio observations, e.g., by LOw-Frequency ARray for radio astronomy (LOFAR) and by relatively deep X-ray observations with good angular resolution, e.g., by the Chandra satellite. We finally show that when misaligned, the jet emission is faint (de-beamed) and missed by current large sky area surveys. Since the isotropic lobe radio emission is also quenched by the CMB cooling, sources with even very powerful jets can go undetected in current radio surveys, and misclassified as radio-quiet AGNs.
The discovery of transiting circumbinary planets by the Kepler mission suggests that planets can form efficiently around binary stars. None of the stellar binaries currently known to host planets has a period shorter than 7 days, despite the large number of eclipsing binaries found in the Kepler target list with periods shorter than a few days. These compact binaries are believed to have evolved from wider orbits into their current configurations via the so-called Lidov-Kozai migration mechanism, in which gravitational perturbations from a distant tertiary companion induce large-amplitude eccentricity oscillations in the binary, followed by orbital decay and circularization due to tidal dissipation in the stars. Here we explore the orbital evolution of planets around binaries undergoing orbital decay by this mechanism. We show that planets may survive and become misaligned from their host binary, or may develop erratic behavior in eccentricity, resulting in their consumption by the stars or ejection from the system as the binary decays. Our results suggest that circumbinary planets around compact binaries could still exist, and we offer predictions as to what their orbital configurations should be like.
We explore trends in galaxy properties with Mpc-scale structures using catalogues of environment and large scale structure from the Galaxy And Mass Assembly (GAMA) survey. Existing GAMA catalogues of large scale structure, group and pair membership allow us to construct galaxy stellar mass functions for different environmental types. To avoid simply extracting the known underlying correlations between galaxy properties and stellar mass, we create a mass matched sample of galaxies with stellar masses between $9.5 \leq \log{M_*/h^{-2} M_{\odot}} \leq 11$ for each environmental population. Using these samples, we show that mass normalised galaxies in different large scale environments have similar energy outputs, $u-r$ colours, luminosities, and morphologies. Extending our analysis to group and pair environments, we show galaxies that are not in groups or pairs exhibit similar characteristics to each other regardless of broader environment. For our mass controlled sample, we fail to see a strong dependence of S\'{e}rsic index or galaxy luminosity on halo mass, but do find that it correlates very strongly with colour. Repeating our analysis for galaxies that have not been mass controlled introduces and amplifies trends in the properties of galaxies in pairs, groups, and large scale structure, indicating that stellar mass is the most important predictor of the galaxy properties we examine, as opposed to environmental classifications.
We present a method to estimate distances to stars with spectroscopically derived stellar parameters. The technique is a Bayesian approach with likelihood estimated via comparison of measured parameters to a grid of stellar isochrones, and returns a posterior probability density function for each star's absolute magnitude. This technique is tailored specifically to data from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) survey. Because LAMOST obtains roughly 3000 stellar spectra simultaneously within each ~5-degree diameter "plate" that is observed, we can use the stellar parameters of the observed stars to account for the stellar luminosity function and target selection effects. This removes biasing assumptions about the underlying populations, both due to predictions of the luminosity function from stellar evolution modeling, and from Galactic models of stellar populations along each line of sight. Using calibration data of stars with known distances and stellar parameters, we show that our method recovers distances for most stars within ~20%, but with some systematic overestimation of distances to halo giants. We apply our code to the LAMOST database, and show that the current precision of LAMOST stellar parameters permits measurements of distances with ~40% error bars. This precision should improve as the LAMOST data pipelines continue to be refined.
This article explores the agreement between the predictions of Modified Newtonian Dynamics (MOND) and the rotation curves and stellar velocity dispersion profiles measured by the DiskMass Survey. A bulge-disk decomposition was made for each of the thirty published galaxies, and a MOND Poisson solver was used to simultaneously compute, from the baryonic mass distributions, model rotation curves and vertical velocity dispersion profiles, which were compared to the measured values. The two main free parameters, the stellar disk's mass-to-light ratio ($M/L$) and its exponential scale-height ($h_z$), were estimated by Markov Chain Monte Carlo modelling. The average best-fit K-band stellar mass-to-light ratio was $M/L \simeq 0.55 \pm 0.15$. However, to match the DiskMass Survey data, the vertical scale-heights would have to be in the range $h_z=200$ to $400$ pc which is a factor of two lower than those derived from observations of edge-on galaxies with a similar scale-length. The reason is that modified gravity versions of MOND characteristically require a larger $M/L$ to fit the rotation curve in the absence of dark matter and therefore predict a stronger vertical gravitational field than Newtonian models. It was found that changing the MOND acceleration parameter, the shape of the velocity dispersion ellipsoid, the adopted vertical distribution of stars, as well as the galaxy inclination, within any realistic range, all had little impact on these results.
Several methods developed within the Pierre Auger Collaboration for the estimation of the muonic component of the Extensive Air Showers observed in the surface Cherenkov detectors are described. The results derived from the data show a deficit of muons predicted by the current hadronic interactions models at ultra-high energies.
In previous work [Amendola {\it et al.}, Phys. Rev. D86 (2012) 063515], Principal Component Analysis based methods to constrain the dark energy equation of state using Type Ia supernovae and other low redshift probes were extended to spectroscopic tests of the stability fundamental couplings, which can probe higher redshifts. Here we use them to quantify the gains in sensitivity obtained by combining spectroscopic measurements expected from ESPRESSO at the VLT and the high-resolution ultra-stable spectrograph for the E-ELT (known as ELT-HIRES) with future supernova surveys. In addition to simulated low and intermediate redshift supernova surveys, we assess the dark energy impact of high-redshift supernovas detected by JWST and characterized by the E-ELT or TMT. Our results show that a detailed characterization of the dark energy properties beyond the acceleration phase (i.e., deep in the matter era) is viable, and may reach as deep as redshift 4.
We propose a new extragalactic but non-cosmological explanation for FRB's based on very young pulsars in supernova remnants. Within a few hundred years of a core-collapse supernova the ejecta is confined within $\sim$1 pc, providing a high enough column density of free electrons for the observed 500-1500 pc/cm$^3$. By extrapolating a Crab-like pulsar to its infancy in an environment like that of SN 1987A, we hypothesize such an object could emit supergiant pulses sporadically which would be bright enough to be seen at a few hundred megaparsecs. In this scenario Faraday rotation at the source gives RM's much larger than the expected cosmological contribution. If the emission were pulsar-like, then the polarization vector could swing over the duration of the burst, which is not expected from non-rotating objects. In this model, the scattering, large DM, and commensurate RM all come from one place which is not the case for the cosmological interpretation. The model also provides testable predictions of the flux distribution and repeat rate of fast radio bursts, and could be further verified by spatial coincidence with optical supernovae of the past several decades.
We use two-dimensional relativistic hydrodynamic numerical calculations to show that highly collimated relativistic jets can be produced in neutron star merger models of short-duration gamma ray bursts without the need for a highly directed engine or a large net magnetic flux. Even a hydrodynamic engine generating a very wide sustained outflow on small scales can in principle produce a highly collimated relativistic jet, facilitated by a dense surrounding medium which provides a cocoon surrounding the jet core. An oblate geometry to the surrounding gas significantly enhances the collimation process. Previous numerical simulations have shown that the merger of two neutron stars produces an oblate, expanding cloud of dynamical ejecta. We show that this gas can efficiently collimate the central engine power much as the surrounding star does in long-duration GRB models. For typical short-duration GRB central engine parameters, we find jets with opening angles of order 10 degrees in which a large fraction of the total outflow power of the central engine resides in highly relativistic material. These results predict large differences in the opening angles of outflows from binary neutron star mergers versus neutron star-black hole mergers.
We demonstrate that tidal evolution of the inner planet (`e') of the system orbiting the star rho 55 Cancri could have led to passage through two secular resonances with other planets in the system. The consequence of this evolution is excitation of both the planetary eccentricity and inclination relative to the original orbital plane. The large mass ratio between the innermost planet and the others means that these excitations can be of substantial amplitude and can have dramatic consequences for the system organisation. Such evolution can potentially explain the large observed mutual inclination between the innermost and outermost planets in the system, and implies that tidal heating could have substantially modified the structure of planet e, and possibly reduced its mass by Roche lobe overflow. Similar inner secular resonances may be found in many multiple planet systems and suggest that many of the innermost planets in these systems could have suffered similar evolutions.
We obtained [O III] narrow-band imaging and multi-slit MXU spectroscopy of the blue compact dwarf (BCD) galaxy NGC 1705 with FORS2@VLT to derive chemical abundances of PNe and H II regions and, more in general, to characterize the properties of the ionized gas. The auroral [O III]\lambda4363 line was detected in all but one of the eleven analyzed regions, allowing for a direct estimate of their electron temperature. The only object for which the [O III]\lambda4363 line was not detected is a possible low-ionization PN, the only one detected in our data. For all the other regions, we derived the abundances of Nitrogen, Oxygen, Neon, Sulfur and Argon out to ~1 kpc from the galaxy center. We detect for the first time in NGC 1705 a negative radial gradient in the oxygen metallicity of -0.24 \pm 0.08 dex kpc^{-1}. The element abundances are all consistent with values reported in the literature for other samples of dwarf irregular and blue compact dwarf galaxies. However, the average (central) oxygen abundance, 12 + log(O/H)=7.98 \pm 0.05, is ~0.2 dex lower than previous literature estimates for NGC 1705 based on the [O III]\lambda4363 line. From classical emission-line diagnostic diagrams, we exclude a major contribution from shock excitation. On the other hand, the radial behavior of the emission line ratios is consistent with the progressive dilution of radiation with increasing distance from the center of NGC~1705. This suggests that the strongest starburst located within the central ~150 pc is responsible for the ionization of the gas out to at least ~1 kpc. The gradual dilution of the radiation with increasing distance from the center reflects the gradual and continuous transition from the highly ionized H II regions in the proximity of the major starburst into the diffuse ionized gas.
Many of the transformative processes in the Universe have taken place in
regions obscured by dust, and are best studied with far-IR spectroscopy. We
present the Cryogenic-Aperture Large Infrared-Submillimeter Telescope
Observatory (CALISTO), a 5-meter class, space-borne telescope actively cooled
to 4 K, emphasizing moderate-resolution spectroscopy in the crucial 35 to 600
micron band. CALISTO will enable NASA and the world to study the rise of heavy
elements in the Universe's first billion years, chart star formation and black
hole growth in dust-obscured galaxies through cosmic time, and conduct a census
of forming planetary systems in our region of the Galaxy. CALISTO will
capitalize on rapid progress in both format and sensitivity of far-IR
detectors. Arrays with a total count of a few 100,000 detector pixels will form
the heart of a suite of imaging spectrometers in which each detector reaches
the photon background limit.
This document contains a large overview paper on CALISTO, as well as six 2-3
page scientific white papers, all prepared in response to NASA's Cosmic Origins
Program Analysis Group (COPAG's) request for input on future mission concepts.
The Far-IR Science Interest Group will meet from 3-5 June 2015 with the
intention of reaching consensus on the architecture for the Far-IR Surveyor
mission. This white paper describes one of the architectures to be considered
by the community. One or more companion papers will describe alternative
architectures.
We report the discovery of SDSS J131326.89-001941.4, an ultra iron-poor red giant star ([Fe/H] ~ -4.3) with a very high carbon abundance ([C/Fe]~ +2.5). This object is the fifth star in this rare class, and the combination of a fairly low effective temperature (Teff ~ 5300 K), which enhances line absorption, with its brightness (g=16.9), makes it possible to measure the abundances of calcium, carbon and iron using a low-resolution spectrum from the Sloan Digital Sky Survey. We examine the carbon and iron abundance ratios in this star and other similar objects in the light of predicted yields from metal-free massive stars, and conclude that they are consistent. By way of comparison, stars with similarly low iron abundances but lower carbon-to-iron ratios deviate from the theoretical predictions.
Merging galaxy clusters leave long-lasting signatures on the baryonic and non-baryonic cluster constituents, including shock fronts, cold fronts, X-ray substructure, radio halos, and offsets between the dark matter and the gas components. Using observations from Chandra, the Jansky Very Large Array, the Giant Metrewave Radio Telescope, and the Hubble Space Telescope, we present a multiwavelength analysis of the merging Frontier Fields cluster MACS J0416.1-2403 (z=0.396), which consists of a NE and a SW subclusters whose cores are separated on the sky by ~250 kpc. We find that the NE subcluster has a compact core and hosts an X-ray cavity, yet it is not a cool core. Approximately 450 kpc south-south west of the SW subcluster, we detect a density discontinuity that corresponds to a compression factor of ~1.5. The discontinuity was most likely caused by the interaction of the SW subcluster with a less massive structure detected in the lensing maps SW of the subcluster's center. For both the NE and the SW subclusters, the dark matter and the gas components are well-aligned, suggesting that MACS J0416.1-2403 is a pre-merging system. The cluster also hosts a radio halo, which is unusual for a pre-merging system. The halo has a 1.4 GHz power of (1.06 +/- 0.09) x 10^{24} W Hz^{-1}, which is somewhat lower than expected based on the X-ray luminosity of the cluster. We suggest that we are either witnessing the birth of a radio halo, or have discovered a rare ultra-steep spectrum halo.
We present $N$-band (8$-$13 $\mu$m) spectroscopic observations of the low-mass, embedded pre-main-sequence close binary system SVS13. Absorption features are clearly detected which are attributable to amorphous silicates, crystalline forsterite, crystalline enstatite and annealed SiO$_{2}$. Most intriguingly, a major component of the dust in the envelope or disc around SVS13 appears to be SiC, required to model adequately both the total intensity and polarisation spectra. Silicon carbide is a species previously detected only in the spectra of C-rich evolved star atmospheres, wherein it is a dust condensate. It has not been unambiguously identified in the interstellar medium, and never before in a molecular cloud, let alone in close proximity to a forming star. Yet pre-Solar grains of SiC have been identified in meteorites, possibly suggesting an interesting parallel between SVS13 and our own Solar-System evolution. The uniqueness of the spectrum suggests that we are either catching SVS13 in a short-lived evolutionary phase and/or that there is something special about SVS13 itself that makes it rare amongst young stars. We speculate on the physical origin of the respective dust species and why they are all simultaneously present toward SVS13. Two scenarios are presented: a disc-instability-induced fragmentation, with subsequent localised heating and orbital evolution firstly annealing initially amorphous silicates and then dispersing their crystalline products throughout a circumstellar disc; and a newly discovered shock-heating mechanism at the interface between the circumstellar and circumbinary discs providing the crystallisation process. One or both of these mechanisms acting on carbon-rich grain material can also feasibly produce the SiC signature.
Advanced inversions of high-resolution spectropolarimetric observations of the He I triplet at 1083 nm are used to generate unique maps of the chromospheric magnetic field vector across a sunspot and its superpenumbral canopy. The observations were acquired by the Facility Infrared Spectropolarimeter (FIRS) at the Dunn Solar Telescope (DST) on 29 January 2012. Multiple atmospheric models are employed in the inversions, as superpenumbral Stokes profiles are dominated by atomic-level polarization while sunspot profiles are Zeeman-dominated but also exhibit signatures perhaps induced by symmetry breaking effects of the radiation field incident on the chromospheric material. We derive the equilibrium magnetic structure of a sunspot in the chromosphere, and further show that the superpenumbral magnetic field does not appear finely structured, unlike the observed intensity structure. This suggests fibrils are not concentrations of magnetic flux but rather distinguished by individualized thermalization. We also directly compare our inverted values with a current-free extrapolation of the chromospheric field. With improved measurements in the future, the average shear angle between the inferred magnetic field and the potential field may offer a means to quantify the non-potentiality of the chromospheric magnetic field to study the onset of explosive solar phenomena.
We study 7530 sunspot umbrae and pores measured by the Hinode Spectropolarimeter (SP) between November 2006 and November 2012. We primarily seek confirmation of the long term secular decrease in the mean magnetic field strength of sunspot umbrae found by Penn and Livingston (2011, IAU Symp. 273,126) between 1998 and 2011. The excellent SP photometric properties and full vector magnetic field determinations from full-Stokes Milne-Eddington inversions are used to address the interrelated properties of the magnetic field strength and brightness temperature for all umbral cores. We find non-linear relationships between magnetic field strength and umbral temperature (and continuum contrast), as well as between umbral radius and magnetic field strength. Using disambiguated vector data, we find that the azimuths measured in the umbral cores reflect an organization weakly influenced by Joy's law. The large selection of umbrae displays a log-normal size spectrum similar to earlier solar cycles. Influenced by the amplitude of the solar cycle and the nonlinear relationship between umbral size and core magnetic field strength, the distribution of core magnetic field strengths, fit most effectively with a skew-normal distribution, shows a weak solar cycle dependence. Yet, the mean magnetic field strength does not show a significant long term trend.
We present extensive calculations of radiative transition rates and electron impact collision strengths for Fe II. The data sets involve 52 levels from the $3d\,^7$, $3d\,^64s$, and $3d\,^54s^2$ configurations. Computations of $A$-values are carried out with a combination of state-of-the-art multiconfiguration approaches, namely the relativistic Hartree--Fock, Thomas--Fermi--Dirac potential, and Dirac--Fock methods; while the $R$-matrix plus intermediate coupling frame transformation, Breit--Pauli $R$-matrix and Dirac $R$-matrix packages are used to obtain collision strengths. We examine the advantages and shortcomings of each of these methods, and estimate rate uncertainties from the resulting data dispersion. We proceed to construct excitation balance spectral models, and compare the predictions from each data set with observed spectra from various astronomical objects. We are thus able to establish benchmarks in the spectral modeling of [Fe II] emission in the IR and optical regions as well as in the UV Fe II absorption spectra. Finally, we provide diagnostic line ratios and line emissivities for emission spectroscopy as well as column densities for absorption spectroscopy. All atomic data and models are available online and through the AtomPy atomic data curation environment.
We present a simple reform for treating the reported problem of loss-of-accuracy near the real axis of Humlicek's w4 algorithm, widely used for the calculation of the Faddeyeva or complex probability function. The reformed routine maintains the claimed accuracy of the algorithm over a wide and fine grid that covers all the domain of the real part, x, of the complex input variable, z=x+iy, and values for the imaginary part in the range y=[10-30, 10+30]
Aims. Optically thin plasmas may deviate from thermal equilibrium and thus,
electrons (and ions) are no longer described by the Maxwellian distribution.
Instead they can be described by $\kappa$-distributions. The free-free spectrum
and radiative losses depend on the temperature-averaged (over the electrons
distribution) and total Gaunt factors, respectively. Thus, there is a need to
calculate and make available these factors to be used by any software that
deals with plasma emission.
Methods. We recalculated the free-free Gaunt factor for a wide range of
energies and frequencies using hypergeometric functions of complex arguments
and the Clenshaw recurrence formula technique combined with approximations
whenever the difference between the initial and final electron energies is
smaller than $10^{-10}$ in units of $z^2Ry$. We used double and quadruple
precisions. The temperature- averaged and total Gaunt factors calculations make
use of the Gauss-Laguerre integration with 128 nodes.
Results. The temperature-averaged and total Gaunt factors depend on the
$\kappa$ parameter, which shows increasing deviations (with respect to the
results obtained with the use of the Maxwellian distribution) with decreasing
$\kappa$. Tables of these Gaunt factors are provided.
As the volume of data grows, astronomers are increasingly faced with choices on what data to keep --- and what to throw away. Recent work evaluating the JPEG2000 (ISO/IEC 15444) standards as a future data format standard in astronomy has shown promising results on observational data. However, there is still a need to evaluate its potential on other type of astronomical data, such as from numerical simulations. GERLUMPH (the GPU-Enabled High Resolution cosmological MicroLensing parameter survey) represents an example of a data intensive project in theoretical astrophysics. In the next phase of processing, the ~27 terabyte GERLUMPH dataset is set to grow by a factor of 100 --- well beyond the current storage capabilities of the supercomputing facility on which it resides. In order to minimise bandwidth usage, file transfer time, and storage space, this work evaluates several data compression techniques. Specifically, we investigate off-the-shelf and custom lossless compression algorithms as well as the lossy JPEG2000 compression format. Results of lossless compression algorithms on GERLUMPH data products show small compression ratios (1.35:1 to 4.69:1 of input file size) varying with the nature of the input data. Our results suggests that JPEG2000 could be suitable for other numerical datasets stored as gridded data or volumetric data. When approaching lossy data compression, one should keep in mind the intended purposes of the data to be compressed, and evaluate the effect of the loss on future analysis. In our case study, lossy compression and a high compression ratio do not significantly compromise the intended use of the data for constraining quasar source profiles from cosmological microlensing.
The last solar minimum is characterized by several peculiar aspects and by
the presence of a complex magnetic topology with two different kinds of coronal
streamers: pseudo-streamers and bipolar streamers. Pseudo-streamers or unipolar
streamer are coronal structures which separate coronal holes of the same
polarity, without a current sheet in the outer corona; unlike bipolar streamer
that separate coronal holes of opposite magnetic polarity. In this study, two
examples of these structures have been identified in the period of Carrington
rotation 2067, by applying a potential-field source-surface extrapolation of
the photospheric field measurements. We present a spectroscopic analysis of a
pseudo-streamer and a bipolar streamer observed in the period 12-17 March 2008
at high spectral and spatial resolution by the Ultraviolet Coronagraph
Spectrometer (UVCS; Kohl et al., 1995) onboard Solar and Heliospheric
Observatory (SOHO). The solar wind plasma parameters, such as kinetic
temperature, electron density and outflow velocity, are inferred in the
extended corona (from 1.7 to 2.1 Rsun) analysing the O VI doublet and Ly alpha
line spectra.
The coronal magnetic topology is taken into account and has been extrapolated
by a 3D magneto-hydrodynamic model of the global corona. The results of the
analysis show some peculiarities of the pseudo-streamer physical parameters in
comparison with those obtained for bipolar streamers: in particular, we have
found higher kinetic temperature and higher outflow velocities of O VI ions and
lower electron density values. In conclusion, we point out that
pseudo-streamers produce a "hybrid" type of outflow that is intermediate
between slow and fast solar wind and they are a possible source of slow/fast
wind in not dipolar solar magnetic field configuration.
We apply a cross-correlation technique to infer the $S>3$mJy radio luminosity function (RLF) from the NRAO VLA sky survey (NVSS) to $z\sim3.5$. We measure $\Sigma$ the over density of radio sources around spectroscopically confirmed quasars. $\Sigma$ is related to the space density of radio sources at the distance of the quasars and the clustering strength between the two samples, hence knowledge of one constrains the other. Under simple assumptions we find $\Phi\propto (1+z)^{3.7\pm0.7}$ out to $z\sim2$. Above this redshift the evolution slows and we constrain the evolution exponent to $<1.01$ ($2\sigma$). This behaviour is almost identical to that found by previous authors for the bright end of the RLF potentially indicating that we are looking at the same population. This suggests that the NVSS is dominated by a single population; most likely radio sources associated with high-excitation cold-mode accretion. Inversely, by adopting a previously modelled RLF we can constrain the clustering of high-redshift radio sources and find a clustering strength consistent with $r_0=15.0\pm 2.5$ Mpc up to $z\sim3.5$. This is inconsistent with quasars at low redshift and some measurements of the clustering of bright FRII sources. This behaviour is more consistent with the clustering of lower luminosity radio galaxies in the local universe. Our results indicate that the high-excitation systems dominating our sample are hosted in the most massive galaxies at all redshifts sampled.
Angular momentum transport in accretion discs is often believed to be due to magnetohydrodynamic turbulence mediated by the magnetorotational instability. Despite an abundant literature on the MRI, the parameters governing the saturation amplitude of the turbulence are poorly understood and the existence of an asymptotic behavior in the Ohmic diffusion regime is not clearly established. We investigate the properties of the turbulent state in the small magnetic Prandtl number limit. Since this is extremely computationally expensive, we also study the relevance and range of applicability of the most common subgrid scale models for this problem. Unstratified shearing boxes simulations are performed both in the compressible and incompressible limits, with a resolution up to 800 cells per disc scale height. The latter constitutes the largest resolution ever attained for a simulation of MRI turbulence. In the presence of a mean magnetic field threading the domain, angular momentum transport converges to a finite value in the small Pm limit. When the mean vertical field amplitude is such that {\beta}, the ratio between the thermal and magnetic pressure, equals 1000, we find {\alpha}~0.032 when Pm approaches zero. In the case of a mean toroidal field for which {\beta}=100, we find {\alpha}~0.018 in the same limit. Both implicit LES and Chollet-Lesieur closure model reproduces these results for the {\alpha} parameter and the power spectra. A reduction in computational cost of a factor at least 16 (and up to 256) is achieved when using such methods. MRI turbulence operates efficiently in the small Pm limit provided there is a mean magnetic field. Implicit LES offers a practical and efficient mean of investigation of this regime but should be used with care, particularly in the case of a vertical field. Chollet-Lesieur closure model is perfectly suited for simulations done with a spectral code.
We investigate the effects of a K-mouflage modification of gravity on the dynamics of clusters of galaxies. We extend the description of K-mouflage to situations where the scalar field responsible for the modification of gravity is coupled to a perfect fluid with pressure. We describe the coupled system at both the background cosmology and cosmological perturbations levels, focusing on cases where the pressure emanates from small-scale nonlinear physics. We derive these properties in both the Einstein and Jordan frames, as these two frames already differ by a few percents at the background level for K-mouflage scenarios, and next compute cluster properties in the Jordan frame that is better suited to these observations. Galaxy clusters are not screened by the K-mouflage mechanism and therefore feel the modification of gravity in a maximal way. This implies that the halo mass function deviates from $\Lambda$-CDM by a factor of order one for masses $M\gtrsim 10^{14} \ h^{-1} M_\odot$. We then consider the hydrostatic equilibrium of gases embedded in galaxy clusters and the consequences of K-mouflage on the X-ray cluster luminosity, the gas temperature and the Sunyaev-Zel'dovich effect. We find that the cluster temperature function, and more generally number counts, are largely affected by K-mouflage, mainly due to the increased cluster abundance in these models. Other scaling relations such as the mass-temperature and the temperature-luminosity relations are only modified at the percent level due to the constraints on K-mouflage from local Solar System tests.
Circumstellar disks are considered to be the birthplace of planets. Specific structures like spiral arms, gaps, and cavities are characteristic indicators of planet-disk interaction. Investigating these structures can provide insights into the growth of protoplanets and the physical properties of the disk. We investigate the feasibility of using molecular lines to trace planet-induced structures in circumstellar disks. Based on 3D hydrodynamic simulations of planet-disk interactions, we perform self-consistent temperature calculations and produce N-LTE molecular line velocity-channel maps and spectra of these disks using our new N-LTE line radiative transfer code Mol3D. Subsequently, we simulate ALMA observations using the CASA simulator. We consider two nearly face-on inclinations, 5 disk masses, 7 disk radii, and 2 different typical pre-main-sequence host stars (T Tauri, Herbig Ae). We calculate up to 141 individual velocity-channel maps for five molecules/isotopoloques in a total of 32 rotational transitions to investigate the frequency dependence of the structures indicated above. We find that the majority of protoplanetary disks in our parameter space could be detected in the molecular lines considered. However, unlike the continuum case, gap detection is not straightforward in lines. For example, gaps are not seen in symmetric rings but are masked by the pattern caused by the global (Keplerian) velocity field. We identify specific regions in the velocity-channel maps that are characteristic of planet-induced structures. Simulations of high angular resolution molecular line observations demonstrate the potential of ALMA to provide complementary information about the planet-disk interaction as compared to continuum observations. In particular, the detection of planet-induced gaps is possible under certain conditions.(abridged)
Magnetic fields permeate the entire solar atmosphere weaving an extremely
complex pattern on both local and global scales. In order to understand the
nature of this tangled web of magnetic fields, its magnetic skeleton, which
forms the boundaries between topologically distinct flux domains, may be
determined. The magnetic skeleton consists of null points, separatrix surfaces,
spines and separators. The skeleton is often used to clearly visualize key
elements of the magnetic configuration, but parts of the skeleton are also
locations where currents and waves may collect and dissipate.
In this review, the nature of the magnetic skeleton on both global and local
scales, over solar cycle time scales, is explained. The behaviour of wave
pulses in the vicinity of both nulls and separators is discussed and so too is
the formation of current layers and reconnection at the same features. Each of
these processes leads to heating of the solar atmosphere, but collectively do
they provide enough heat, spread over a wide enough area, to explain the energy
losses throughout the solar atmosphere? Here, we consider this question for the
three different solar regions: active regions, open-field regions and the quiet
Sun.
We find that the heating of active regions and open-field regions is highly
unlikely to be due to reconnection or wave dissipation at topological features,
but it is possible that these may play a role in the heating of the quiet Sun.
In active regions, the absence of a complex topology may play an important role
in allowing large energies to build up and then, subsequently, be explosively
released in the form of a solar flare. Additionally, knowledge of the intricate
boundaries of open-field regions (which the magnetic skeleton provides) could
be very important in determining the main acceleration mechanism(s) of the
solar wind.
We present spectral and energy dependent timing characteristics of the hard X-ray transient IGR J17497-2821 based on XMM-Newton observations performed five and nine days after its outburst on 2006 September 17. We find that the source spectra can be well described by a hard (Gamma ~ 1.50) powerlaw and a weak multicolour disk blackbody with inner disk temperature kT_{in} ~ 0.2 KeV. A broad iron K - alpha line with FWHM ~ 27000 Km/s, consistent with that arising from an accretion disk truncated at large radius, was also detected. The power density spectra of IGR J17497 - 2821, derived from the high resolution (30 micro second) timing mode XMM-Newton observations, are characterised by broadband noise components that are well modelled by three Lorentzians. The shallow power law slope, low disk luminosity and the shape of the broadband power density spectrum indicate that the source was in the hard state. The rms variability in the softer energy bands (0.3-2 KeV) found to be ~ 1.3 times that in 2-5 and 5-10 KeV energy bands. We also present the energy dependent timing analysis of the RXTE/PCA data, where we find that at higher energies, the rms variability increases with energy.
We continue the study of collisionless systems governed by additive $r^{-\alpha}$ interparticle forces by focusing on the influence of the force exponent $\alpha$ on radial orbital anisotropy. In this preparatory work we construct the radially anisotropic Osipkov-Merritt phase-space distribution functions for self-consistent spherical Hernquist models with $r^{-\alpha}$ forces and $1\leq\alpha<3$. The resulting systems are isotropic at the center and increasingly dominated by radial orbits at radii larger than the anisotropy radius $r_a$. For radially anisotropic models we determine the minimum value of the anisotropy radius $r_{ac}$ as a function of $\alpha$ for phase-space consistency (such that the phase-space distribution function is nowhere negative for $r_a\geq r_{ac}$). We find that $r_{ac}$ decreases for decreasing $\alpha$, and that the amount of kinetic energy that can be stored in the radial direction relative to that stored in the tangential directions for marginally consistent models increases for decreasing $\alpha$. In particular, we find that isotropic systems are consistent in the explored range of $\alpha$. By means of direct $N$-body simulations we finally verify that the isotropic systems are also stable.
We have analysed a sample of 574 Spitzer 4.5 micron-selected galaxies with [4.5]<23 and Ks>24 (AB) over the UltraVISTA ultra-deep COSMOS field. Our aim is to investigate whether these mid-IR bright, near-IR faint sources contribute significantly to the overall population of massive galaxies at redshifts z>=3. By performing a spectral energy distribution (SED) analysis using up to 30 photometric bands, we have determined that the redshift distribution of our sample peaks at redshifts z~2.5-3.0, and ~32% of the galaxies lie at z>=3. We have studied the contribution of these sources to the galaxy stellar mass function (GSMF) at high redshifts. We found that the [4.5]<23, Ks>24 galaxies produce a negligible change to the GSMF previously determined for Ks<24 sources at 3=<z<4, but their contribution is more important at 4=<z<5, accounting for >~50% of the galaxies with stellar masses Mst>~6 x 10^10 Msun. We also constrained the GSMF at the highest-mass end (Mst>~2 x 10^11 Msun) at z>=5. From their presence at 5=<z<6, and virtual absence at higher redshifts, we can pinpoint quite precisely the moment of appearance of the first most massive galaxies as taking place in the ~0.2 Gyr of elapsed time between z~6 and z~5. Alternatively, if very massive galaxies existed earlier in cosmic time, they should have been significantly dust-obscured to lie beyond the detection limits of current, large-area, deep near-IR surveys.
Context. The prototypical low-mass young stellar object, T Tauri, is a well-studied multiple system with at least three components. Aims. We aim to explore the T Tau system with the highest spatial resolution, study the time evolution of the known components, and re-determine the orbital parameters of the stars. Methods. Near-infrared classical imaging and integral field spectrograph observations were obtained during the Science Verification of SPHERE, the new high-contrast imaging facility at the VLT. The obtained FWHM of the primary star varies between 0.050" and 0.059", making these the highest spatial resolution near-infrared images of the T Tauri system obtained to date. Results. Our near-infrared images confirm the presence of extended emission south of T Tau Sa, reported in the literature. New narrow-band images show, for the first time, that this feature shows strong emission in both the Br-{\gamma} and H2 1-0 S(1) lines. Broadband imaging at 2.27 {\mu}m shows that T Tau Sa is 0.92 mag brighter than T Tau Sb, which is in contrast to observations from Jan. 2014 (when T Tau Sa was fainter than Sb), and demonstrates that T Tau Sa has entered a new period of high variability. The newly obtained astrometric positions of T Tau Sa and Sb agree with orbital fits from previous works. The orbit of T Tau S (the center of gravity of Sa and Sb) around T Tau N is poorly constrained by the available observations and can be fit with a range of orbits ranging from a nearly circular orbit with a period of 475 years to highly eccentric orbits with periods up to 2.7*10^4 years. We also detected a feature south of T Tau N, at a distance of $144 \pm 3$ mas, which shows the properties of a new companion.
The Kepler mission has yielded the discovery of eight eclipsing binaries, within period range of 7 - 40 d, hosting circumbinary planets. This is longer than the typical eclipsing binary period found by Kepler, and hence there is a dearth of planets around the closest binaries. In this paper we demonstrate how this dearth may be explained by the presence of a distant stellar tertiary companion, which shrunk the inner binary orbit by the process of Kozai cycles and tidal friction, a mechanism that has been implicated for producing most binaries with periods below 7 d. We show that the geometry and orbital dynamics of these evolving triple-star systems are highly restrictive for a circumbinary planet, which is subject itself to Kozai modulation, on one hand, and can shield the two inner stars from their Kozai cycle and subsequent shrinking, on the other hand. Only small planets on wide and inclined orbits may form, survive and allow for the inner binary shrinkage. Those are difficult to detect.
Aim: The late stages of stellar evolution are mainly governed by the mass of the stars. Low- and intermediate-mass stars lose copious amounts of mass during the asymptotic giant branch (AGB) which obscure the central star making it difficult to study the stellar spectra and determine the stellar mass. In this study, we present observational data that can be used to determine lower limits to the stellar mass. Method: Spectra of nine heavily reddened AGB stars taken by the Herschel Space Observatory display numerous molecular emission lines. The strongest emission lines are due to H2O. We search for the presence of isotopologues of H2O in these objects. Result: We detected the 16O and 17O isotopologues of water in these stars, but lines due to H2^{18}O are absent. The lack of 18O is predicted by a scenario where the star has undergone hot-bottom burning which preferentially destroys 18O relative to 16O and 17O. From stellar evolution calculations, this process is thought to occur when the stellar mass is above 5 Msun for solar metallicity. Hence, observations of different isotopologues of H2O can be used to help determine the lower limit to the initial stellar mass. Conclusion: From our observations, we deduce that these extreme OH/IR stars are intermediate-mass stars with masses of >= 5 Msun. Their high mass-loss rates of ~ 1.0e-4 Msun/yr may affect the enrichment of the interstellar medium and the overall chemical evolution of our Galaxy.
We find significant fluctuations of angular momentum within the convective helium shell of a pre-collapse massive star - a core-collapse supernova progenitor - which may facilitate the formation of accretion disks and jets that can explode the star. The convective flow in our model of an evolved M_ZAMS=15Msun star, computed with the sub-sonic hydrodynamic solver MAESTRO, contains entire shells with net angular momentum in different directions. Such a distribution of angular momentum may give rise to several episodes of accretion disks with varying axes around the newly formed neutron star or black hole. The accretion disks in turn might launch jets that can explode the star in the frame of the jittering-jets model.
This article reviews a few topics relevant to Galactic cosmic-ray astrophysics, focusing on the recent AMS-02 data release and Fermi Large Area Telescope data on the diffuse Galactic gamma-ray emissivity. Calculations are made of the diffuse cosmic-ray induced p+p --> pi^0 --> 2 gamma spectra, normalized to the AMS-02 cosmic-ray proton spectrum at ~ 10 - 100 GV, with and without a hardening in the cosmic-ray proton spectrum at rigidities R >~ 300 GV. A single power-law momentum "shock" spectrum for the local interstellar medium cosmic-ray proton spectrum cannot be ruled out from the gamma-ray emissivity data alone without considering the additional contribution of electron bremsstrahlung. Metallicity corrections are discussed, and a maximal range of nuclear enhancement factors from 1.52 to 1.92 is estimated.Origins of the 300 GV cosmic-ray proton and alpha-particle hardening are discussed.
LSQ14bdq and SN 2006oz are super-luminous, hydrogen-poor, SNe with double-humped light curves. We show that a Quark-Nova (QN; explosive transition of the neutron star to a quark star) occurring in a massive binary, experiencing two Common Envelope (CE) phases, can quantitatively explain the light curves of LSQ14bdq and SN 2006oz. The more massive component (A) explodes first as a normal SN, yielding a Neutron Star which ejects the hydrogen envelope of the companion when the system enters its first CE phase. During the second CE phase, the NS spirals into and inflates the second He-rich CE. In the process it gains mass and triggers a Quark-Nova, outside of the CO core, leaving behind a Quark Star. The first hump in our model is the QN shock re-energizing the expanded He-rich CE. Subsequent merging of the Quark Star with the CO core of component B turns the Quark star to a Black Hole. The ensuing Black Hole accretion provides sufficient power for the second brighter and long lasting hump. Our model suggests a possible connection between SLSNe-I and type Ic-BL SNe which occur when the Quark Nova is triggered inside the CO core.
We present spectroscopic and photometric data of the peculiar SN 2001gh, discovered by the 'Southern inTermediate Redshift ESO Supernova Search' (STRESS) at a redshift z=0.16. SN 2001gh has relatively high luminosity at maximum (M_B = -18.55 mag), while the light curve shows a broad peak. An early-time spectrum shows an almost featureless, blue continuum with a few weak and shallow P-Cygni lines that we attribute to HeI. HeI lines remain the only spectral features visible in a subsequent spectrum, obtained one month later. A remarkable property of SN 2001gh is the lack of significant spectral evolution over the temporal window of nearly one month separating the two spectra. In order to explain the properties of SN 2001gh, three powering mechanism are explored, including radioactive decays of a moderately large amount of 56Ni, magnetar spin-down, and interaction of SN ejecta with circumstellar medium. We favour the latter scenario, with a SN Ib wrapped in a dense, circumstellar shell. The fact that no models provide an excellent fit with observations, confirms the troublesome interpretation of the nature of SN 2001gh. A rate estimate for SN 2001gh-like event is also provided, confirming the intrinsic rarity of these objects.
We examine the Chevallier-Polarski-Linder (CPL) parametrization, in the context of quintessence and barotropic dark energy models, to determine the subset of such models to which it can provide a good fit. The CPL parametrization gives the equation of state parameter $w$ for the dark energy as a linear function of the scale factor $a$, namely $w = w_0 + w_a(1-a)$. In the case of quintessence models, we find that over most of the $w_0$, $w_a$ parameter space the CPL parametrization maps onto a fairly narrow form of behavior for the potential $V(\phi)$, while a one-dimensional subset of parameter space, for which $w_a = \kappa (1+w_0)$, with $\kappa$ constant, corresponds to a wide range of functional forms for $V(\phi)$. For barotropic models, we show that the functional dependence of the pressure on the density, up to a multiplicative constant, depends only on $w_i = w_a + w_0$ and not on $w_0$ and $w_a$ separately. Our results suggest that the CPL parametrization is not optimal for testing either type of model.
We present deep, 170 ks, Chandra X-ray observations of Abell 2219 (z=0.23) one of the hottest and most X-ray luminous clusters known, and which is experiencing a major merger event. We discover a 'horseshoe' of high temperature gas surrounding the ram-pressure-stripped, bright, hot, X-ray cores. We confirm an X-ray shock front located north-west of the X-ray centroid and along the projected merger axis. We also find a second shock front to the south-east of the X-ray centroid making this only the second cluster where both the shock and reverse shock are confirmed with X-ray temperature measurements. We also present evidence for a sloshing cold front in the 'remnant tail' of one of the sub-cluster cores. The cold front and north-west shock front geometrically bound the radio halo and appear to be directly influencing the radio properties of the cluster.
Grids of stellar evolution are required in many fields of astronomy/astrophysics, such as planet hosting stars, binaries, clusters, chemically peculiar stars, etc. In this study, a grid of stellar evolution models with updated ingredients and {recently determined solar abundaces} is presented. The solar values for the initial abundances of hydrogen, heavy elements and mixing-length parameter are 0.0172, 0.7024 and 1.98, respectively. The mass step is small enough (0.01 M$_\odot$) that interpolation for a given star mass is not required. The range of stellar mass is 0.74 to 10.00 M$_\odot$. We present results in different forms of tables for easy and general application. The second stellar harmonic, required for analysis of apsidal motion of eclipsing binaries, is also listed. We also construct rotating models to determine effect of rotation on stellar structure and derive fitting formula for luminosity, radius and the second stellar harmonic as a function of rotational parameter. We also compute and list colours and bolometric corrections of models required for transformation between theoretical and observational results. The results are tested for the Sun, the Hyades cluster, the slowly rotating chemically peculiar Am stars and the eclipsing binaries with apsidal motion. The theoretical and observational results along isochrones are in good agreement. The grids are also applicable to rotating stars provided that equatorial velocity is given.
AA Tau is a well studied young stellar object that presents many of the photometric characteristics of a Classical T Tauri star (CTTS), including short-timescale stochastic variability attributed to spots and/or accretion as well as long duration dimming events attributed to occultations by vertical features (e.g., warps) in its circumstellar disk. We present new photometric observations of AA Tau from the Kilodegree Extremely Little Telescope North (KELT-North) which reveal a deep, extended dimming event in 2011, which we show supports the interpretation by Bouvier et al. (2013) of an occultation by a high-density feature in the circumstellar disk located >8 AU from the star. We also present KELT-North observations of V409 Tau, a relatively unstudied young stellar object also in Taurus-Auriga, showing short timescale erratic variability, along with two separate long and deep dimming events, one from January 2009 through late October 2010, and the other from March 2012 until at least September 2013. We interpret both dimming events to have lasted more than 600 days, each with a depth of ~1.4 mag. From a spectral energy distribution analysis, we propose that V409 Tau is most likely surrounded by a circumstellar disk viewed nearly edge-on, and using Keplerian timescale arguments we interpret the deep dimmings of V409 Tau as occultations from one or more features within this disk >10 AU from the star. In both AA Tau and V409 Tau, the usual CTTS short-timescale variations associated with accretion processes close to the stars continue during the occultations, further supporting the distant occulting material interpretation. Like AA Tau, V409 Tau serves as a laboratory for studying the detailed structure of the protoplanetary environments of T Tauri disks, specifically disk structures that may be signposts of planet formation at many AU out in the disk.
We study lensing by voids in Cubic Galileon and Nonlocal gravity cosmologies, which are examples of theories of gravity that modify the lensing potential. We find voids in the dark matter and halo density fields of N-body simulations and compute their lensing signal analytically from the void density profiles, which we show are well fit by a simple analytical formula. In the Cubic Galileon model, the modifications to gravity inside voids are not screened and they approximately double the size of the lensing effects compared to GR. The difference is largely determined by the direct effects of the fifth force on lensing and less so by the modified density profiles. For this model, we also discuss the subtle impact on the force and lensing calculations caused by the screening effects of haloes that exist in and around voids. In the Nonlocal model, the impact of the modified density profiles and the direct modifications to lensing are comparable, but they boost the lensing signal by only $\approx 10\%$, compared with that of GR. Overall, our results suggest that lensing by voids is a promising tool to test models of gravity that modify lensing.
Massive stars are usually found in binaries, and binaries with periods less than 10 days may have a preference for near equal component masses. In this paper we investigate the evolution of these binaries all the way to contact and the possibility that these systems can be progenitors of double neutron star binaries. The small orbital separations of observed double neutron star binaries suggest that the progenitor systems underwent a common envelope phase at least once during their evolution. Bethe & Brown (1998) proposed that massive binary twins will undergo a common envelope evolution while both components are ascending the red giant branch or asymptotic giant branch simultaneously, also known as double-core evolution. Using models generated from the stellar evolution code Evolve Zero Age Main Sequence, we determine the range of mass ratios resulting in both components simultaneously ascending the RGB or AGB as a function of the difference in birth times, t. We find that, even for a generous t=5 Myr, the minimum mass ratio qmin=0.933 for an 8 Solar Mass primary and increases for larger primaries. We use a hydrodynamics code, StarSmasher, to study specifically the evolution of q=1 common envelope systems as a function of initial component mass, age, and orbital separation. We find the dynamical stability limit, the largest orbital separation where the binary becomes dynamically unstable, as a function of the component mass and age. Finally, we calculate the efficiency of ejecting matter during the inspiral phase to extrapolate the properties of the remnant binary from our numerical results, assuming the common envelope is completely ejected. We find that for the nominal core masses, there is a minimum orbital separation for a given component mass such that the helium cores survive common envelope evolution in a tightly bound binary and are viable progenitors for double neutron stars.
We have examined high accuracy radial velocities of Cepheids to determine the binary frequency. The data are largely from the CORAVEL spectrophotometer and the Moscow version, with a typical uncertainty of $\leq1$~km~s$^{-1}$, and a time span from 1 to 20 years. A systemic velocity was obtained by removing the pulsation component using a high order Fourier series. From this data we have developed a list of stars showing no orbital velocity larger than $\pm1$~km~s$^{-1}$. The binary fraction was analyzed as a function of magnitude, and yields an apparent decrease in this fraction for fainter stars. We interpret this as incompleteness at fainter magnitudes, and derive the preferred binary fraction of $29\pm8$\% ( $20\pm6$\% per decade of orbital period) from the brightest 40 stars. Comparison of this fraction in this period range (1-20 years) implies a large fraction for the full period range. This is reasonable in that the high accuracy velocities are sensitive to the longer periods and smaller orbital velocity amplitudes in the period range sampled here. Thus the Cepheid velocity sample provides a sensitive detection in the period range between short period spectroscopic binaries and resolved companions. The recent identification of $\delta$ Cep as a binary with very low amplitude and high eccentricity underscores the fact that the binary fractions we derive are lower limits, to which other low amplitude systems will probably be added. The mass ratio (q) distribution derived from ultraviolet observations of the secondary is consistent with a flat distribution for the applicable period range (1 to 20 years).
We present the gravitational waveforms computed in ab initio two-dimensional core collapse supernova models evolved with the Chimera code for progenitor masses between 12 and 25 solar masses. All models employ multi-frequency neutrino transport in the ray-by-ray approximation, state-of-the-art weak interaction physics, relativistic transport corrections such as the gravitational redshift of neutrinos, two-dimensional hydrodynamics with the commensurate relativistic corrections, Newtonian self-gravity with a general relativistic monopole correction, and the Lattimer-Swesty equation of state with 220 MeV compressibility, and begin with the most recent Woosley-Heger nonrotating progenitors in this mass range. All of our models exhibit robust explosions. Therefore, our waveforms capture all stages of supernova development: 1) a relatively short and weak prompt signal, 2) a quiescent stage, 3) a strong signal due to convection and SASI activity, 4) termination of active accretion onto the proto-neutron star, and 5) a slowly increasing tail that reaches a saturation value. Fourier decomposition shows that the gravitational wave signals we predict should be observable by AdvLIGO for Galactic events across the range of progenitors considered here. The fundamental limitation of these models is in their imposition of axisymmetry. Further progress will require counterpart three-dimensional models, which are underway.
In this work we present the results of imaging simulations performed with the help of the GEANT4 package for the protoMIRAX hard X-ray balloon experiment. The instrumental background was simulated taking into account the various radiation components and their angular dependence, as well as a detailed mass model of the experiment. We modeled the meridian transits of the Crab Nebula and the Galatic Centre region during balloon flights in Brazil ($\sim -23^{\circ}$ of latitude and an altitude of $\sim 40 \thinspace$ km) and introduced the correspondent spectra as inputs to the imaging simulations. We present images of the Crab and of three sources in the Galactic Centre region: 1E 1740.7-2942, GRS 1758-258 and GX 1+4. The results show that the protoMIRAX experiment is capable of making spectral and timing observations of bright hard X-ray sources as well as important imaging demonstrations that will contribute to the design of the MIRAX satellite mission.
Since the end of the eighties and in response to a reported increase in the total neutrino flux in the Homestake experiment in coincidence with solar flares, solar neutrino detectors have searched for solar flare signals. Even though these detectors have used different solar flare samples and analyses, none of them has been able to confirm the possible signal seen by Homestake. Neutrinos from the decay of mesons, which are themselves produced in collisions of accelerated ions with the solar atmosphere would provide a novel window on the underlying physics of the hadronic acceleration and interaction processes during solar flares. Solar flare neutrino flux measurements would indeed help to constrain current parameters such as the composition of the accelerated flux, the proton/ion spectral index and the high energy cutoff or the magnetic configuration in the interaction region. We describe here a new way to search for these neutrinos by considering a specific solar flare sample and a data driven time window template which will improve the likelihood of neutrino detection.
Abundances of Fe, Si, Ni, Ti, Na, Mg, Cu, Zn, Mn, Cr and Ca in the atmosphere of the K-dwarf HD 77338 are determined and discussed. HD 77338 hosts a hot Uranus-like planet and is currently the most metal-rich single star to host any planet. Determination of abundances was carried out in the framework of a self-consistent approach developed by Pavlenko et al. (2012). Abundances were computed iteratively by the program ABEL8, and the process converged after 4 iterations. We find that most elements follow the iron abundance, however some of the iron peak elements are found to be over-abundant in this star.
Magnetized neutron stars constitute a special class of compact objects harbouring gravitational fields that deviate strongly from the Newtonian weak field limit. Moreover strong electromagnetic fields anchored into the star give rise to non-linear corrections to Maxwell equations described by quantum electrodynamics (QED). Electromagnetic fields close to or above the critical value of $\BQ=4.4\times10^9$~T are probably present in some pulsars and for most of the magnetars. To account properly for emission emanating from the neutron star surface like for instance thermal radiation and its polarization properties, it is important to include general relativistic (GR) effects simultaneously with non-linear electrodynamics. This can be achieved through a 3+1 formalism known in general relativity and that incorporates QED perturbations to Maxwell equations. Starting from the lowest order corrections to the Lagrangian for the electromagnetic field, as given for instance by Born-Infeld or Euler-Heisenberg theory, we derive the non-linear Maxwell equations in general relativity including quantum vacuum effects. We also derive a prescription for the force-free limit and show that these equations can be solved with classical finite volume methods for hyperbolic conservation laws. It is therefore straightforward to include general relativity and quantum electrodynamics in the description of neutron star magnetospheres by using standard classical numerical techniques borrowed from Maxwell and Newton theory. As an application, we show that spin-down luminosity corrections associated to QED effects are negligible with respect to GR corrections.
We present multiwavelength imaging observations of PKS 1045-188, 8C 1849+670, and PKS 2216-038, three radio-loud active galactic nuclei from the MOJAVE-Chandra Sample that straddle the Fanaroff-Riley (FR) boundary between low- and high-power jets. These hybrid sources provide an excellent opportunity to study jet emission mechanisms and the influence of the external environment. We used archival VLA observations, and new Hubble and Chandra observations to identify and study the spectral properties of five knots in PKS 1045-188, two knots in 8C 1849+670, and three knots in PKS 2216-038. For the seven X-ray visible knots, we constructed and fit the broadband spectra using synchrotron and inverse Compton/cosmic microwave background (IC/CMB) emission models. In all cases, we found that the lack of detected optical emission ruled out the X-ray emission from the same electron population that produces radio emission. All three sources have high total extended radio power, similar to that of FR II sources. We find this is in good agreement with previously studied hybrid sources, where high-power hybrid sources emit X-rays via IC/CMB and the low-power hybrid sources emit X-rays via synchrotron emission. This supports the idea that it is total radio power rather than FR morphology that determines the X-ray emission mechanism. We found no significant asymmetries in the diffuse X-ray emission surrounding the host galaxies. Sources PKS 1045-188 and 8C 1849+670 show significant differences in their radio and X-ray termination points, which may result from the deceleration of highly relativistic bulk motion.
We study relations between global characteristics of low-redshift (0 < z < 1) compact star-forming galaxies, including absolute optical magnitudes, Hbeta emission-line luminosities (or equivalently star-formation rates), stellar masses, and oxygen abundances. The sample consists of 5182 galaxies with high-excitation HII regions selected from the SDSS DR7 and SDSS/BOSS DR10 surveys adopting a criterion [OIII]4959/Hbeta > 1. These data were combined with the corresponding data for high-redshift (2 < z < 3) star-forming galaxies. We find that in all diagrams low-z and high-z star-forming galaxies are closely related indicating a very weak dependence of metallicity on stellar mass, redshift, and star-formation rate. This finding argues in favour of the universal character of the global relations for compact star-forming galaxies with high-excitation HII regions over redshifts 0 < z < 3.
We perform a time-resolved spectral analysis of GRB 130606B within the framework of a fast-cooling synchrotron radiation model with magnetic field strength in the emission region decaying with time, as proposed by Uhm & Zhang. The data from all time intervals can be successfully fit by the model. The same data can be equally well fit by the empirical Band function with typical parameter values. Our results, which involve only minimal physical assumptions, offer one natural solution to the origin of the observed GRB spectra and imply that, at least some, if not all, Band-like GRB spectra with typical Band parameter values can indeed be explained by synchrotron radiation.
Complex organic molecules are ubiquitous companions of young low-mass protostars. Recent observations suggest that their emission stems, not only from the traditional hot corino, but also from offset positions. In this work, 2D physicochemical modelling of an envelope-cavity system is carried out. Wavelength-dependent radiative transfer calculations are performed and a comprehensive gas-grain chemical network is used to simulate the physical and chemical structure. The morphology of the system delineates three distinct regions: the cavity wall layer with time-dependent and species-variant enhancements; a torus rich in complex organic ices, but not reflected in gas-phase abundances; and the remaining outer envelope abundant in simpler solid and gaseous molecules. Strongly irradiated regions, such as the cavity wall layer, are subject to frequent photodissociation in the solid phase. Subsequent recombination of the photoproducts leads to frequent reactive desorption, causing gas-phase enhancements of several orders of magnitude. This mechanism remains to be quantified with laboratory experiments. Direct photodesorption is found to be relatively inefficient. If radicals are not produced directly in the icy mantle, the formation of complex organics is impeded. For efficiency, a sufficient number of FUV photons needs to penetrate the envelope; and elevated cool dust temperatures need to enable grain-surface radical mobility. As a result, a high stellar luminosity and a sufficiently wide cavity favor chemical complexity. Furthermore within this paradigm, complex organics are demonstrated to have unique lifetimes and be grouped into early (formaldehyde, ketene, methanol, formic acid, methyl formate, acetic acid, glycolaldehyde) and late (acetaldehyde, dimethyl ether, ethanol) species.
We provide a prescription for setting initial conditions for cosmological N-body simulations, which simultaneously employ Lagrangian meshes (`particles') and Eulerian grids (`fields'). Our description is based on coordinate systems in arbitrary geometry, and can therefore be used in any metric theory of gravity. We apply our prescription to a choice of Effective Field Theory of Modified Gravity, and show how already in the linear regime, particle trajectories are curved. For some viable models of modified gravity, the Dark Matter trajectories are affected at the level of 5% at Mpc scales. Moreover, we show initial conditions for a simulation where a scalar modification of gravity is modelled in a Lagrangian particle-like description.
It has long been known that dissipation is a crucial ingredient in the superradiant amplification of wavepackets off rotating objects. We show that, once appropriate dissipation mechanisms are included, stars are also prone to superradiance and superradiant instabilities. In particular, ultra-light dark matter with small interaction cross section with the star material or self-annihilation can trigger a superradiant instability. On long timescales, the instability strips the star of most of its angular momentum. Whether or not new stationary configurations surrounded by scalar condensates exist, remains to be seen.
Using the concept of cracking, we have explored the influence of density fluctuations on isotropic and anisotropic charged matter configurations in General Relativity with "barotropic" equations of state, $P = P(\rho)$ and $P_{\perp}= P_{\perp}(\rho)$ and a mass-charge relation $Q=Q(\rho)$. We have refined the idea that density fluctuations affect physical variables and their gradients, i.e. the radial pressure and charge density gradients. It is found that not only anisotropic charged models could present cracking (or overturning), but also isotropic charged matter configurations could be affected by density fluctuations.
An excess in $\gamma$-rays emanating from the galactic centre has recently been observed in the Fermi-LAT data. We investigate the new exciting possibility of fitting the signal spectrum by dark matter annihilating dominantly to a Higgs-pseudoscalar pair. We show that the fit to the $\gamma$-ray excess for the Higgs-pseudoscalar channel can be just as good as for annihilation into bottom-quark pairs. This channel arises naturally in a full model such as the next-to-minimal supersymmetric Standard Model (NMSSM) and we find regions where dark matter relic density, the $\gamma$-ray signal and other experimental constraints, can all be satisfied simultaneously. Annihilation into scalar pairs allows for the possibility of detecting the Higgs or pseudoscalar decay into two photons, providing a smoking-gun signal of the model.
We characterize the expected statistical errors with which the parameters of black-hole binaries can be measured from gravitational-wave (GW) observations of their inspiral, merger and ringdown by a network of second-generation ground-based GW observatories. We simulate a population of black-hole binaries with uniform distribution of component masses in the interval $(3,80)~M_\odot$, distributed uniformly in comoving volume, with isotropic orientations. From signals producing signal-to-noise ratio $\geq 5$ in at least two detectors, we estimate the posterior distributions of the binary parameters using the Bayesian parameter estimation code LALInference. The GW signals will be redshifted due to the cosmological expansion and we measure only the "redshifted" masses. By assuming a cosmology, it is possible to estimate the gravitational masses by inferring the redshift from the measured posterior of the luminosity distance. We find that the measurement of the gravitational masses will be in general dominated by the error in measuring the luminosity distance. In spite of this, the component masses of more than $50\%$ of the population can be measured with accuracy better than $\sim 25\%$ using the Advanced LIGO-Virgo network. Additionally, the mass of the final black hole can be measured with median accuracy $\sim 18\%$. Spin of the final black hole can be measured with median accuracy $\sim 5\% ~(17\%)$ for binaries with non-spinning (aligned-spin) black holes. Additional detectors in Japan and India significantly improve the accuracy of sky localization, and moderately improve the estimation of luminosity distance, and hence, that of all mass parameters. We discuss the implication of these results on the observational evidence of intermediate-mass black holes and the estimation of cosmological parameters using GW observations.
The loop quantum dynamics of Kantowski-Sachs spacetime and the interior of higher genus black hole spacetimes with a cosmological constant has some peculiar features not shared by various other spacetimes in loop quantum cosmology. As in the other cases, though the quantum geometric effects resolve the physical singularity and result in a non-singular bounce, after the bounce a spacetime with small spacetime curvature does not emerge in either the subsequent backward or the forward evolution. Rather, in the asymptotic limit the spacetime manifold is a product of two constant curvature spaces. Interestingly, though the spacetime curvature of these asymptotic spacetimes is very high, their effective metric is a solution to the Einstein's field equations. Analysis of the components of the Ricci tensor shows that after the singularity resolution, the Kantowski-Sachs spacetime leads to an effective metric which can be interpreted as the `charged' Nariai, while the higher genus black hole interior can similarly be interpreted as anti Bertotti-Robinson spacetime with a cosmological constant. These spacetimes are `charged' in the sense that the energy momentum tensor that satisfies the Einstein's field equations is formally the same as the one for the uniform electromagnetic field, albeit it has a purely quantum geometric origin. The asymptotic spacetimes also have an emergent cosmological constant which is different in magnitude, and sometimes even its sign, from the cosmological constant in the Kantowski-Sachs and the interior of higher genus black hole metrics. With a fine tuning of the latter cosmological constant, we show that `uncharged' Nariai, and anti Bertotti-Robinson spacetimes with a vanishing emergent cosmological constant can also be obtained.
We study the phenomenon of discrete symmetry breaking during the inflationary epoch, using a model-independent approach based on the effective field theory of inflation. We work in a context where both time reparameterization symmetry and spatial diffeomorphism invariance can be broken during inflation. We determine the leading derivative operators in the quadratic action for fluctuations that break parity and time-reversal. Within suitable approximations, we study their consequences for the dynamics of linearized fluctuations. We find that fluctuations in the scalar sector can acquire a direction-dependent phase. For the tensor sector, we show that one of the polarization modes can be significantly amplified throughout the whole period of inflation.
An accelerated universe should naturally have a vacuum energy density determined by its dynamical curvature. The cosmological constant is most likely a temporary description of a dynamical variable that has been drastically evolving from the early inflationary era to the present. In this Essay we propose a unified picture of the cosmic history implementing such an idea, in which the cosmological constant problem is fixed at early times. All the main stages, from inflation and its (``graceful'') exit into a standard radiation regime, as well as the matter and dark energy epochs, are accounted for. Finally, we show that for a generic Grand Unified Theory associated to the inflationary phase, the amount of entropy generated from primeval vacuum decay can explain the huge measured value today.
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