We use HST/WFC3 imaging to study the red population in the IR-selected, X-ray detected, low-mass cluster Cl J1449+0856 at z=2, one of the few bona-fide established clusters discovered at this redshift, and likely a typical progenitor of an average massive cluster today. This study explores the presence and significance of an early red sequence in the core of this structure, investigating the nature of red sequence galaxies, highlighting environmental effects on cluster galaxy populations at high redshift, and at the same time underlining similarities and differences with other distant dense environments. Our results suggest that the red population in the core of Cl J1449+0856 is made of a mixture of quiescent and dusty star-forming galaxies, with a seedling of the future red sequence already growing in the very central cluster region, and already characterising the inner cluster core with respect to lower density environments. On the other hand, the color-magnitude diagram of this cluster is definitely different from that of lower-redshift (z<1) clusters, as well as of some rare particularly evolved massive clusters at similar redshift, and it is suggestive of a transition phase between active star formation and passive evolution occurring in the proto-cluster and established lower-redshift cluster regimes.
In this work, two new axisymmetric models for the Galactic mass distribution are presented. Motivated by recent results, these two models include the contribution of a stellar thin disc and of a thick disc, as massive as the thin counterpart but with a shorter scale-length. Both models satisfy a number of observational constraints: stellar densities at the solar vicinity, thin and thick disc scale lengths and heights, rotation curve(s), and the absolute value of the perpendicular force Kz as a function of distance to the Galactic centre. We numerically integrate into these new models the motion of all Galactic globular clusters for which distances, proper motions, and radial velocities are available, and the orbits of about one thousand stars in the solar vicinity. The retrieved orbital characteristics are compared to those obtained by integrating the clusters and stellar orbits in pure thin disc models. We find that, due to the possible presence of a thick disc, the computed orbital parameters of disc stars can vary by as much as 30-40%. We also show that the systematic uncertainties that affect the rotation curve still plague computed orbital parameters of globular clusters by similar amounts.
The mass function of freshly formed star clusters is empirically often described as a power law. However the cluster mass function of populations of young clusters over the scale of a galaxy has been found to be described by a Schechter-function. Here we address this apparent discrepancy. We assume that in an annulus of an isolated self- regulated radially-exponential axially-symmetric disk galaxy, the local mass function of very young (embedded) clusters is a power law with an upper mass limit which depends on the local star formation rate density. Radial integration of this mass function yields a galaxy-wide embedded cluster mass function. This integrated embedded cluster mass function has a Schechter-type form, which results from the addition of many low mass clusters forming at all galactocentric distances and rarer massive clusters only forming close to the center of the galaxy.
We study the abundance of subhaloes in the hydrodynamical cosmological simulation Illustris, which includes both baryons and dark matter in a $\Lambda$CDM volume 106.5 Mpc a side. We compare Illustris to its dark matter-only (DMO) analog, Illustris-Dark, and quantify the effects of baryonic processes on the demographics of subhaloes in the host mass range $10^{11}$ to $3 \times 10^{14} M_\odot$. We focus on both the evolved ($z=0$) subhalo cumulative mass functions (SHMF) and the statistics of subhaloes ever accreted, i.e. infall subhalo mass function. We quantify the variance in subhalo abundance at fixed host mass and investigate the physical reasons responsible for such scatter. We find that in Illustris, baryonic physics impacts both the infall and $z=0$ subhalo abundance by tilting the DMO function and suppressing the abundance of low-mass subhaloes. The breaking of self-similarity in the subhalo abundance at $z=0$ is enhanced by the inclusion of baryonic physics. The non-monotonic alteration of the evolved subhalo abundances can be explained by the modification of the concentration--mass relation of Illustris hosts compared to Illustris-Dark. Interestingly, the baryonic implementation in Illustris does not lead to an increase in the halo-to-halo variation compared to Illustris-Dark. In both cases, the fractional intrinsic scatter today is larger for Milky Way-like haloes than for cluster-sized objects. For Milky Way-like haloes, it increases from about eight per cent at infall to about 25 per cent at the current epoch. In both runs, haloes of fixed mass formed later host more subhaloes than early formers.
A key challenge in understanding the feedback mechanism of AGN in Brightest Cluster Galaxies (BCGs) is the inherent rarity of catching an AGN during its strong outburst phase. This is exacerbated by the ambiguity of differentiating between AGN and clusters in X-ray observations. If there is evidence for an AGN then the X-ray emission is commonly assumed to be dominated by the AGN emission, introducing a selection effect against the detection of AGN in BCGs. In order to recover these 'missing' clusters, we systematically investigate the colour-magnitude relation around some ~3500 ROSAT All Sky Survey selected AGN, looking for signs of a cluster red sequence. Amongst our 22 candidate systems, we independently rediscover several confirmed systems, where a strong AGN resides in a central galaxy. We compare the X-ray luminosity to red sequence richness distribution of our AGN candidate systems with that of a similarly selected comparison sample of ~1000 confirmed clusters and identify seven 'best' candidates (all of which are BL Lac objects), where the X-ray flux is likely to be a comparable mix between cluster and AGN emission. We confirm that the colours of the red sequence are consistent with the redshift of the AGN, that the colours of the AGN host galaxy are consistent with AGN, and, by comparing their luminosities with those from our comparison clusters, confirm that the AGN hosts are consistent with BCGs.
The mass of the Local Group (LG) is a crucial parameter for galaxy formation theories. However, its observational determination is challenging - its mass budget is dominated by dark matter which cannot be directly observed. To meet this end the posterior distributions of the LG and its massive constituents have been constructed by means of constrained and random cosmological simulations. Two priors are assumed - the LCDM model that is used to set up the simulations and a LG model,which encodes the observational knowledge of the LG and is used to select LG-like objects from the simulations. The constrained simulations are designed to reproduce the local cosmography as it is imprinted onto the Cosmicflows-2 database of velocities. Several prescriptions are used to define the LG model, focusing in particular on different recent estimates of the tangential velocity of M31. It is found that (a) different $v_{tan}$ choices affect the peak mass values up to a factor of 2, and change mass ratios of $M_{M31}$ to $M_{MW}$ by up to 20%; (b) constrained simulations yield more sharply peaked posterior distributions compared with the random ones; (c) LG mass estimates are found to be smaller than those found using the timing argument; (d) preferred MW masses lie in the range of $(0.6 - 0.8)\times10^{12} M_{\odot}$ whereas (e) $M_{M31}$ is found to vary between $(1.0 - 2.0)\times10^{12} M_{\odot}$, with a strong dependence on the $v_{tan}$ values used.
We used the updated [Fe/H] abundances of 168 F-G type dwarfs and calibrated them to a third order polynomial in terms of reduced ultraviolet excess, $\delta_{0.41}$ defined with $ugr$ data in the SDSS. We estimated the $M_g$ absolute magnitudes for the same stars via the re-reduced Hipparcos parallaxes and calibrated the absolute magnitude offsets, $\Delta M_g$, relative to the intrinsic sequence of Hyades to a third order polynomial in terms of $\delta_{0.41}$. The ranges of the calibrations are $-2<$[Fe/H]$\leq$0.3 dex and $4<M_g\leq6$ mag. The mean of the residuals and the corresponding standard deviation for the metallicity calibration are 0 and 0.137 mag; while, for the absolute magnitude calibration they are 0 and 0.179 mag, respectively. We applied our procedures to 23,414 dwarf stars in the Galactic field with the Galactic coordinates $85^{\circ}\leq b\leq90^{\circ}$, $0^{\circ}\leq l\leq360^{\circ}$ and size 78 deg$^{2}$. We estimated absolute magnitude $M_g$ dependent vertical metallicity gradients as a function of vertical distance $Z$. The gradients are deep in the range of $0<Z\leq5$ kpc, while they are very small positive numbers beyond $Z=5$ kpc. All dwarfs with $5<M_g\leq6$ mag are thin-disc stars and their distribution shows a mode at $(g-r)_0\approx 0.38$ mag, while the absolute magnitudes $4<M_g\leq5$ are dominated by thick disc and halo stars, i.e. the apparently bright ones ($g_0\leq18$ mag) are thick-disc stars with a mode at $(g-r)_0\sim0.38$ mag, while the halo population is significant in the faint stars ($g_0>18$ mag).
The polarization properties of extragalactic radio sources at frequencies higher than 20 GHz are still poorly constrained. However, their characterization would provide invaluable information about the physics of the emission processes and is crucial to estimate their contamination as foregrounds of the polarized cosmic microwave background (CMB) angular power spectrum on scales < 30 arcmin. In this contribution, after summarizing the state-of-the-art of polarimetric observations in the millimetric wavelength bands, we present our observations of a complete sample of 53 sources with S > 200 mJy (at 20 GHz) carried out with the Australia Telescope Compact Array between 5.5 and 38 GHz. The analysis clearly shows that polarization properties cannot be simply inferred from total intensity ones, as the spectral behaviors of the two signals are typically different.
This paper presents 828 new 21 cm neutral hydrogen line measurements carried out with the FORT receiver of the meridian transit Nan\c{c}ay radio telescope (NRT) in the years 2000 -- 2007. This observational program was part of a larger project aimed at collecting an exhaustive and magnitude-complete HI extragalactic catalog for Tully-Fisher applications. Through five massive data releases, the KLUN series has collected a homogeneous sample of 4876 HI-spectra of spiral galaxies, complete down to a flux of 5 Jy.km.s^{-1} and with declination delta > -40{\deg}. We publish here the last release of the KLUN HI observational program, corresponding to the faint end of the survey, with HI masses ranging from 5 10^8 to 5 10^{10} solar masses. The size of this final sample is comparable to the catalogs based on the Arecibo and Parkes radio telescope campaigns, and it allows general HI mass distribution studies from a set of homogeneous radio measurements.
Context: The damped random walk (DRW) stochastic process is nowadays frequently used to model aperiodic light curves of AGNs. A number of correlations between the DRW model parameters, the signal decorrelation timescale and amplitude, and the physical AGN parameters such as the black hole mass or luminosity have been reported. Aims: We are interested in whether it is plausible to correctly measure the DRW parameters from a typical ground-based survey, in particular how accurate the recovered DRW parameters are compared to the input ones. Methods: By means of Monte Carlo simulations of AGN light curves, we study the impact of the light curve length, the source magnitude, cadence, and additional light on the DRW model parameters. Results: The most significant finding is that currently existing surveys are going to return unconstrained DRW decorrelation timescales, because typical rest-frame data do not probe long enough timescales or the white noise part of PSD for DRW. The experiment length must be at least ten times longer than the true DRW timescale, being presumably in the vicinity of one year, meaning a minimum 10-years-long AGN light curves (rest-frame). The DRW timescales for sufficiently long light curves are typically weakly biased, and the exact bias depends on the fitting method and used priors. The DRW amplitude is mostly affected by the photometric noise (so the source magnitude or the signal-to-noise ratio), cadence, and the AGN host light. Conclusions: Because the DRW parameters appear to be incorrectly determined from typically existing data, the reported correlations of the DRW variability and physical AGN parameters from other works seem unlikely to be correct. In particular, the anti-correlation of the DRW timescale with redshift is a manifestation of the survey length being too short. Application of DRW to modeling typical AGN optical light curves is questioned.
Outflows in active galactic nuclei (AGNs) are crucial to understand in investigating the co-evolution of supermassive black holes (SMBHs) and their host galaxies since outflows may play an important role as an AGN feedback mechanism. Based on the archival UV spectra obtained with HST and IUE, we investigate outflows in the broad-line region (BLR) in low-redshift AGNs (z < 0.4) through the detailed analysis of the velocity profile of the CIV emission line. We find a dependence of the outflow strength on the Eddington ratio and the BLR metallicity in our low-redshift AGN sample, which is consistent with the earlier results obtained for high-redshift quasars. These results suggest that the BLR outflows, gas accretion onto SMBH, and past star-formation activity in the host galaxies are physically related in low-redshift AGNs as in powerful high-redshift quasars.
Accounting for nebular emission when modeling galaxy spectral energy distributions (SEDs) is important, as both line and continuum emission can contribute significantly to the total observed flux. In this work, we present a new nebular emission model integrated within the Flexible Stellar Population Synthesis code that computes the total line and continuum emission for complex stellar populations using the photoionization code Cloudy. The self-consistent coupling of the nebular emission to the matched ionizing spectrum produces emission line intensities that correctly scale with the stellar population as a function of age and metallicity. This more complete model of galaxy SEDs will improve estimates of global gas properties derived with diagnostic diagrams, star formation rates based on H$\alpha$, and stellar masses derived from NIR broadband photometry. Our models agree well with results from other photoionization models and are able to reproduce observed emission from H II regions and star-forming galaxies. Our models show improved agreement with the observed H II regions in the Ne III/O II plane and show satisfactory agreement with He II emission from $z=2$ galaxies when including rotating stellar models. Models including post-asymptotic giant branch stars are able to reproduce line ratios consistent with low-ionization emission regions (LIERs).
Understanding the evolution of galaxies and in particular their star formation history is a central challenge of modern cosmology. Theoretical scenarios will be constrained by future ultra deep radio surveys. In this paper we present an analytical tool for analyzing radio data. Our physical model, based on an analytical description of the steady-state cosmic ray spectrum, explains the correlation between the non-thermal radio flux and the star formation rate (SFR). As cosmic rays are produced in supernova remnants, their injection rate is proportional to the supernova rate and thus also to the SFR. When these highly energetic charged particles travel in the magnetized interstellar medium they emit synchrotron radiation. As a result there is a relation between the SFR and the non-thermal radio emission. A crucial point is that synchrotron emission can be absorbed again by the free-free mechanism. This suppression becomes stronger with increasing number density of the gas, more precisely of the free electrons, and with decreasing frequency. We present an estimate of the critical frequency above which radio emission can be used as a tracer for the SFR. If the observed galaxy is redshifted, this critical frequency moves along with other spectral features to lower values in the observing frame. The method can therefore be successfully applied at high redshift. However, for high redshift, i.e. > 5 , and observations at high radio frequency bands, i.e. > 50 GHz, special caution should be paid, as the observed flux might be dominated by free-free emission or the thermal contribution.
We have combined observations of Galactic high-velocity HI from two surveys: a very sensitive survey from the Green Bank 140ft Telescope with limited sky coverage, and the less sensitive but complete Galactic All Sky Survey from the 64m Parkes Radio Telescope. The two surveys preferentially detect different forms of neutral gas due to their sensitivity. We adopt a machine learning approach to divide our data into two populations that separate across a range in column density: 1) a narrow line-width population typical of the majority of bright high velocity cloud components, and 2) a fainter, broad line-width population that aligns well with that of the population found in the Green Bank survey. We refer to these populations as dense and diffuse gas respectively, and find that diffuse gas is typically located at the edges and in the tails of high velocity clouds, surrounding dense components in the core. A fit to the average spectrum of each type of gas in the Galactic All Sky Survey data reveals the dense population to have a typical line width of ~20 km/s and brightness temperature of ~0.3 K, while the diffuse population has a typical line width of ~30 km/s and a brightness temperature of ~0.2 K. Our results confirm that most surveys of high velocity gas in the Milky Way halo are missing the majority of the ubiquitous diffuse gas, and that this gas is likely to contribute at least as much mass as the dense gas.
We present a search for transient and highly variable sources at low radio frequencies (150-200 MHz) that explores long timescales of 1-3 years. We conducted this search by comparing the TIFR GMRT Sky Survey Alternative Data Release 1 (TGSS ADR1) and the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey catalogues. To account for the different completeness thresholds in the individual surveys, we searched for compact GLEAM sources above a flux density limit of 100 mJy that were not present in the TGSS ADR1; and also for compact TGSS ADR1 sources above a flux density limit of 200 mJy that had no counterpart in GLEAM. From a total sample of 234 333 GLEAM sources and 275 612 TGSS ADR1 sources in the overlap region between the two surveys, there were 99658 GLEAM sources and 38 978 TGSS ADR sources that passed our flux density cutoff and compactness criteria. Analysis of these sources resulted in three candidate transient sources. Further analysis ruled out two candidates as imaging artefacts. We analyse the third candidate and show it is likely to be real, with a flux density of 182 +/- 26 mJy at 147.5 MHz. This gives a transient surface density of rho = (6.2 +/- 6) x 10-5 deg-2 . We present initial follow-up observations and discuss possible causes for this candidate. The small number of spurious sources from this search demonstrates the high reliability of these two new low-frequency radio catalogues.
We summarize results of the analysis of the optical variability of the continuum and emission-line fluxes in the 3C390.3 nucleus during 1992-2014. The [OIII]5007 flux increases monotonically by $\approx$30 per cent in 2003-2014. The narrow Balmer lines show similar monotonic increase, while the variability patterns of the [OI]6300 narrow line are completely different from that of [OIII]. The reverberation lags are found to be 88.6$\pm$8.4, 161$\pm$15, and 113$\pm$14d for the H$\beta$, H$\alpha$, and H$\gamma$ broad emission-lines, respectively. The reverberation mass of the central black hole equals to (1.87$\pm$0.26)$\times10^9\,M_\odot$ and (2.81$\pm$0.38)$\times10^9\,M_\odot$, for the H$\beta$ and H$\alpha$ lines and assuming a scaling factor that converts the virial product to a mass to be f=5.5. A difference between both masses can point to a difference between kinematics of the H$\alpha$ and H$\beta$ emission regions. We show that the reverberation mapping can only be applied to the entire period of observations of the 3C390.3 nucleus after removing a long-term trend. This trend has been expressed by a slowly varying scalefactor c(t) in the power-law relationship between the line and continuum fluxes: $F_{line}\propto c(t)\,F_{cont}^a$. We find the power-law index $a$ equals to 0.77 and 0.54 for the H$\beta$ and H$\alpha$ lines, respectively. The observed relationship between the Balmer decrement and the optical continuum flux is as follows: $F(H\alpha)/F(H\beta) \propto F_{cont}^{-0.20}$ and $F(H\beta)/F(H\gamma) \propto F_{cont}^{-0.18}$. The 3C390.3 nucleus is an "outsider" in the relationship between optical luminosity and black hole mass. Its Eddington ratio is $E_{bol}/E_{Edd}$ = 0.0037.
We study the alignment of galaxies relative to their local environment in SDSS-DR8 and, using these data, we discuss evolution scenarios for different types of galaxies. We defined a vector field of the direction of anisotropy of the local environment of galaxies. We summed the unit direction vectors of all close neighbours of a given galaxy in a particular way to estimate this field. We found the alignment angles between the spin axes of disc galaxies, or the minor axes of elliptical galaxies, and the direction of anisotropy. The distributions of cosines of these angles are compared to the random distributions to analyse the alignment of galaxies. Sab galaxies show perpendicular alignment relative to the direction of anisotropy in a sparse environment, for single galaxies and galaxies of low luminosity. Most of the parallel alignment of Scd galaxies comes from dense regions, from 2...3 member groups and from galaxies with low luminosity. The perpendicular alignment of S0 galaxies does not depend strongly on environmental density nor luminosity; it is detected for single and 2...3 member group galaxies, and for main galaxies of 4...10 member groups. The perpendicular alignment of elliptical galaxies is clearly detected for single galaxies and for members of < 11 member groups; the alignment increases with environmental density and luminosity. We confirm the existence of fossil tidally induced alignment of Sab galaxies at low z. The alignment of Scd galaxies can be explained via the infall of matter to filaments. S0 galaxies may have encountered relatively massive mergers along the direction of anisotropy. Major mergers along this direction can explain the alignment of elliptical galaxies. Less massive, but repeated mergers are possibly responsible for the formation of elliptical galaxies in sparser areas and for less luminous elliptical galaxies.
We analyze in detail the spatial distribution and kinematic properties of two different stellar populations in Andromeda II (And II) dwarf spheroidal galaxy. We obtained their detailed surface density maps, together with their radial density profiles. The two populations differ not only in age and metallicity, but also in their spatial distribution and kinematics. Old stars ($\gtrsim 11$ Gyr) follow a round distribution well fitted by truncated density profiles. These stars rotate around the projected optical major axis of the galaxy with line-of-sight velocities $v_{los}(r_h) = 16 \pm 3$ km s$^{-1}$ and a velocity gradient of $2.06 \pm 0.21$ km s$^{-1}$ arcmin$^{-1}$. Intermediate-age stars ($\lesssim 9$ Gyr) concentrate in the centre of the galaxy and form an elongated structure extending along the projected optical major axis. This structure appears to rotate with a steeper velocity gradient, $2.24 \pm 0.22$ km s$^{-1}$ arcmin$^{-1}$, and around the optical minor axis. The centres of rotation and kinetic position angles (PA$_{\rm kin}$) of both populations differ. For intermediate-age stars we obtained PA$_{\rm kin} = 18^\circ \pm 2^\circ$ and for the old ones PA$_{\rm kin} = 63^\circ \pm 3^\circ$ in good agreement with photometric PA measured from isopleths fitted to the photometry. We conclude that the two stellar populations may not be in equilibrium and thus confirm the scenario in which And II formed as a result of a merger at redshift $z\sim 1.75$.
The paper presents new results of the ongoing study of the unusual Lynx-Cancer void galaxy DDO 68 with record-low-metallicity regions (12+log(O/H) ~7.14) of the current star formation (SF). They include: a) a new spectrum and photometry with the 6-m SAO RAS telescope (BTA) for the Luminous Blue Variable (LBV = DDO68-V1). Photometric data sets are complemented with those based on the Sloan Digital Sky Survey (SDSS) and the Hubble Space Telescope (HST) archive images; b) the analysis of the DDO~68 supergiant shell (SGS) and the prominent smaller H-alpha arcs/shells visible at the HST image coupled with kinematics maps in H-alpha obtained with the Fabry-Perot interferometer (FPI) at the BTA; c) the list of identified at the HST images of about 50 most luminous stars (-9.1 < M_V < -6.0 mag) related to star-forming regions with the known extremely low O/H. This is intended to pave the path for the actual science with the next generation of giant telescopes. We confirm the earlier hints on significant variations of the LBV optical light deriving its amplitude of dV > 3.7~mag for the first time. New data suggest that in 2008--2010 the LBV reached M_V = --10.5 and probably underwent a giant eruption. We argue that the structure of star-forming complexes along the SGS (`Northern Ring') perimeter provides evidence for the sequential induced SF episodes caused by the shell gas instabilities and gravitational collapse. The variability of some DDO~68 luminous extremely metal-poor stars can be monitored with medium-size telescopes at sites with superb seeing.
The role of magnetic fields in the early stages of star formation is not well constrained. In order to discriminate between different star formation models, we analyze 3D magnetohydrodynamic simulations of low-mass cores and explore the correlation between magnetic field orientation and outflow orientation over time. We produce synthetic observations of dust polarization at resolutions comparable to millimeter-wave dust polarization maps observed by CARMA and compare these with 2D visualizations of projected magnetic field and column density. Cumulative distribution functions of the projected angle between the magnetic field and outflow show different degrees of alignment in simulations with differing mass-to-flux ratios. The distribution function for the less magnetized core agrees with observations finding random alignment between outflow and field orientations, while the more magnetized core exhibits stronger alignment. We find that fractional polarization increases when the system is viewed such that the magnetic field is close to the plane of the sky, and the values of fractional polarization are consistent with observational measurements. The simulation outflow, which reflects the underlying angular momentum of the accreted gas, changes direction significantly over the first $\sim0.1$ Myr of evolution. This movement could lead to the observed random alignment between outflows and the magnetic fields in protostellar cores.
We present a search for companion [CII] emitters to known luminous sources at $6<$ z $<6.5$ in deep ALMA observations. Our data is deep enough to detect sources down to L$_{\rm [CII]} \sim 10^8$ at z $\sim6$. We identify five robust line detections from a blind search of five deep fields centered on ultra-luminous infrared galaxies and QSOs, suggesting these objects may be highly biased tracers of mass in the early Universe. We find these companion lines to have comparable properties to other known galaxies at the same epoch. All companions lie less than 650 km s$^{-1}$ and between 20-70 kpc (projected) from their central source, providing a constraint on their average halo masses of 1.4$\times$10$^{12}$ M$_\odot$. To place these discoveries in context, we employ a mock galaxy catalog to estimate the luminosity function for [CII] during reionization and compare to our observations. The simulations support this result by showing a similar level of elevated counts found around such luminous sources. Finally we explore the effects of these biased tracers on the measurement of the [CII] power spectrum for upcoming intensity mapping experiments.
An analytical method for investigation of the evolution of dynamical systems {\it with independent on time accuracy} is developed for perturbed Hamiltonian systems. The error-free estimation using of computer algebra enables the application of the method to complex multi-dimensional Hamiltonian and dissipative systems. It also opens principal opportunities for the qualitative study of chaotic trajectories. The performance of the method is demonstrated on perturbed two-oscillator systems. It can be applied to various non-linear physical and astrophysical systems, e.g. to the long-term planetary dynamics.
On the basis of the Poincare-Weyl gauge theory of gravitation, a new conformal Weyl-Dirac theory of gravitation is proposed, which is a gravitational theory in Cartan-Weyl spacetime with the Dirac scalar field representing the dark matter model. A static approximate axially symmetric solution of the field equations in vacuum is obtained. On the base of this solution in the Newtonian approximation one considers the problem of rotation velocities in spiral components of galaxies.
The origin of the cosmic-ray knee has remained a puzzle since its discovery over 60 years. In addition, Some latest experiments have revealed a spectral cutoff of the electron around 1 TeV. We find these two spectral breaks have a similar Lorentz factor $\sim 10^6$, and interpret this similarity with a threshold interaction induced by a new particle X abundant in the Galaxy. The interaction process $CR \ + \ X \ \longrightarrow \ CR \ + \ X^{\prime}$ can take place when the effective energy is sufficient to convert it into the mass of another unknown particle $X^{\prime}$ (as a representative to all possible threshold inelastic interactions), where the mass of $X^{\prime}$ is $10^6$ higher than that of the X with respect to the above mentioned common Lorentz factor. Thus cosmic rays will lose their energy above the threshold and produce a spectral break. Under this scenario, we can reproduce the spectral break for both the nuclei and electron, and predict a flattened spectrum for electrons after the cutoff. Given that there are uncertainties of experiments in determining the actual spectra of these breaks and their components, our model allows a wide mass range of the particle X from ultra low value to around 1 eV.
We present ALMA 1.3 mm continuum, 12CO, C18O, and SO data for the Class 0 protostars, Lupus 3 MMS, IRAS 15398-3559, and IRAS 16253-2429 at resolutions of ~100 AU. By measuring a rotational profile in C18O, a 100 AU Keplerian disk around a 0.3 Msun protostar is observed in Lupus 3 MMS. No 100 AU Keplerian disks are observed in IRAS 15398-3559 and IRAS 16253-2429. Nevertheless, embedded compact (<30 AU) continuum components are detected. The C18O emission in IRAS 15398-3559 shows signatures of infall with a constant angular momentum. IRAS 16253-2429 exhibits signatures of infall and rotation, but its rotational profile is unresolved. By fitting the C18O data with our kinematic models, the protostellar masses and the disk radii are inferred to be 0.01 Msun and 20 AU in IRAS 15398-3559, and 0.03 Msun and 6 AU in IRAS 16253-2429. By comparing the specific angular momentum profiles from 10,000 to 100 AU in 8 Class 0 and I protostars, we find that the evolution of envelope rotation can be described with conventional inside-out collapse models. In comparison with a sample of 18 protostars with known disk radii, our results reveal signs of disk growth, with the disk radius increasing as M*^{0.8+/-0.14} or t^{1.09+\-0.37} in the Class 0 stage, where M* is the protostellar mass and t is the age. The disk growth rate slows down in the Class I stage. Besides, we find a hint that the mass accretion rate declines as t^{-0.26+\-0.04} from the Class 0 to I stages.
The open cluster Berkeley 90 is the home to one of the most massive binary systems in the Galaxy, LS III +46$^{\circ}$11, formed by two identical, very massive stars (O3.5 If* + O3.5 If*), and a second early-O system (LS III +46$^{\circ}$12 with an O4.5 IV((f)) component at least). Stars with spectral types earlier than O4 are very scarce in the Milky Way, with no more than 20 examples. The formation of such massive stars is still an open question today, and thus the study of the environments where the most massive stars are found can shed some light on this topic. To this aim, we determine the properties and characterize the population of Berkeley 90 using optical, near-infrared and WISE photometry and optical spectroscopy. This is the first determination of these parameters with accuracy. We find a distance of $3.5^{+0.5}_{-0.5}$ kpc and a maximum age of 3 Ma. The cluster mass is around $1000$ $M_{\odot}$ (perhaps reaching $1500$ $M_{\odot}$ if the surrounding population is added), and we do not detect candidate runaway stars in the area. There is a second population of young stars to the Southeast of the cluster that may have formed at the same time or slightly later, with some evidence for low-activity ongoing star formation.
We present ProFit, a new code for Bayesian two-dimensional photometric galaxy
profile modelling. ProFit consists of a low-level C++ library (libprofit),
accessible via a command-line interface and documented API, along with
high-level R (ProFit) and Python (PyProFit) interfaces (available at
github.com/ICRAR/ libprofit, github.com/ICRAR/ProFit, and
github.com/ICRAR/pyprofit respectively). R ProFit is also available pre-built
from CRAN, however this version will be slightly behind the latest GitHub
version. libprofit offers fast and accurate two- dimensional integration for a
useful number of profiles, including Sersic, Core-Sersic, broken-exponential,
Ferrer, Moffat, empirical King, point-source and sky, with a simple mechanism
for adding new profiles. We show detailed comparisons between libprofit and
GALFIT. libprofit is both faster and more accurate than GALFIT at integrating
the ubiquitous Serrsic profile for the most common values of the Serrsic index
n (0.5 < n < 8).
The high-level fitting code ProFit is tested on a sample of galaxies with
both SDSS and deeper KiDS imaging. We find good agreement in the fit
parameters, with larger scatter in best-fit parameters from fitting images from
different sources (SDSS vs KiDS) than from using different codes (ProFit vs
GALFIT). A large suite of Monte Carlo-simulated images are used to assess
prospects for automated bulge-disc decomposition with ProFit on SDSS, KiDS and
future LSST imaging. We find that the biggest increases in fit quality come
from moving from SDSS- to KiDS-quality data, with less significant gains moving
from KiDS to LSST.
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A detailed examination of new high quality radio catalogues (e.g. Cornish) in combination with available mid-infrared (MIR) satellite imagery (e.g. Glimpse) has allowed us to find 70 new planetary nebula (PN) candidates based on existing knowledge of their typical colors and fluxes. To further examine the nature of these sources, multiple diagnostic tools have been applied to these candidates based on published data and on available imagery in the HASH (Hong Kong/ AAO/ Strasbourg H{\alpha} planetary nebula) research platform. Some candidates have previously-missed optical counterparts allowing for spectroscopic follow-up. Indeed, the single object spectroscopically observed so far has turned out to be a bona fide PN.
A massive primordial halo near an intensely star forming galaxy may collapse into a supermassive star (SMS) and leave a massive black hole seed of about $10^5~M_{sun}$. To investigate the impact of ionizing radiation on the formation of an SMS from a nearby galaxy, we perform three-dimensional radiation hydrodynamical simulations by selecting a pair of massive dark matter halos forming at $z >10$. We find that rich structures such as clumps and filaments around the source galaxy shield the cloud from ionizing radiation. In fact, in some cases cloud collapse is accelerated under ionizing radiation. This fact suggests that the ionization of the cloud's surroundings helps its collapse. Only strong radiation at the early stage of structure formation can halt the cloud collapse, but this is much stronger than observationally allowed value. We also explored the effect of ionizing radiation on a sample of 68 halos by employing an analytical model and found that increase in the mean density of the gas between the SMS forming cloud and the source galaxy protects the gas cloud from ionizing radiation as they approach each other. Thus, we conclude that ionizing radiation does not prevent the formation of an SMS in most of the cases.
We revisit the evolution of the mass-metallicity relation of low- and high-redshift galaxies by using a sample of local analogs of high-redshift galaxies. These analogs share the same location of the UV-selected star-forming galaxies at $z\sim2$ on the [OIII]/H$\beta$ versus [NII]/H$\alpha$ nebular emission-line diagnostic (or BPT) diagram. Their physical properties closely resemble those in $z\sim2$ UV-selected star-forming galaxies being characterized in particular by high ionization parameters ($\log q\approx7.9$) and high electron densities ($n_e\approx100~\rm{cm}^{-3}$). With the full set of well-detected rest-frame optical diagnostic lines, we measure the gas-phase oxygen abundance in the SDSS galaxies and these local analogs using the empirical relations and the photoionization models. We find that the metallicity difference between the SDSS galaxies and our local analogs in the $8.5<log(M_*/M_{\odot})<9.0$ stellar mass bin varies from -0.09 to 0.39 dex, depending on strong-line metallicity measurement methods. Due to this discrepancy the evolution of mass-metallicity should be used to compare with the cosmological simulations with caution. We use the [SII]/H$\alpha$ and [OI]/H$\alpha$ BPT diagram to reduce the potential AGN and shock contamination in our local analogs. We find that the AGN/shock influences are negligible on the metallicity estimation.
RR Lyrae stars may be the best practical tracers of Galactic halo (sub-)structure and kinematics. The PanSTARRS1 (PS1) $3\pi$ survey offers multi-band, multi-epoch, precise photometry across much of the sky, but a robust identification of RR Lyrae stars in this data set poses a challenge, given PS1's sparse, asynchronous multi-band light curves ($\lesssim 12$ epochs in each of five bands, taken over a 4.5-year period). We present a novel template fitting technique that uses well-defined and physically motivated multi-band light curves of RR Lyrae stars, and demonstrate that we get accurate period estimates, precise to 2 sec in $>80\%$ of cases. We augment these light curve fits with other {\em features} from photometric time-series and provide them to progressively more detailed machine-learned classification models. From these models we are able to select the widest ($3/4$ of the sky) and deepest (reaching 120 kpc) sample of RR Lyrae stars to date. The PS1 sample of $\sim 35,000$ RRab stars is pure (90%), and complete (80% at 80 kpc) at high galactic latitudes. It also provides distances precise to 3%, measured with newly derived period-luminosity relations for optical/near-infrared PS1 bands. With the addition of proper motions from {\em Gaia} and radial velocity measurements from multi-object spectroscopic surveys, we expect the PS1 sample of RR Lyrae stars to become the premier source for studying the structure, kinematics, and the gravitational potential of the Galactic halo. The techniques presented in this study should translate well to other sparse, multi-band data sets, such as those produced by the Dark Energy Survey and the upcoming Large Synoptic Survey Telescope Galactic plane sub-survey.
In light of recent observational results indicating an apparent lack of correlation between the Anomalous Microwave Emission (AME) and mid-infrared emission from polycyclic aromatic hydrocarbons (PAHs), we assess whether rotational emission from spinning silicate and/or iron nanoparticles could account for the observed AME without violating observational constraints on interstellar abundances, ultraviolet extinction, and infrared emission. By modifying the SpDust code to compute the rotational emission from these grains, we find that nanosilicate grains could account for the entirety of the observed AME, whereas iron grains could be responsible for only a fraction, even for extreme assumptions on the amount of interstellar iron concentrated in ultrasmall iron nanoparticles. Given the added complexity of contributions from multiple grain populations to the total spinning dust emission, as well as existing uncertainties due to the poorly-constrained grain size, charge, and dipole moment distributions, we discuss generic, carrier-independent predictions of spinning dust theory and observational tests that could help identify the AME carrier(s).
We present a proper motion measurement for the halo globular cluster Pyxis, using HST/ACS data as the first epoch, and GeMS/GSAOI Adaptive Optics data as the second, separated by a baseline of about 5 years. This is both the first measurement of the proper motion of Pyxis and the first calibration and use of Multi-Conjugate Adaptive Optics data to measure an absolute proper motion for a faint, distant halo object. Consequently, we present our analysis of the Adaptive Optics data in detail. We obtain a proper motion of mu_alpha cos(delta)=0.89+/-0.30 mas/yr and mu_delta=0.62+/-0.29 mas/yr. From the proper motion and the line-of-sight velocity we find the orbit of Pyxis is rather eccentric with its apocenter at 100 to 400 kpc and its pericenter at about 27 kpc. We also investigate two literature-proposed associations for Pyxis with the recently discovered ATLAS stream and the Magellanic system. Combining our measurements with dynamical modeling and cosmological numerical simulations we find it unlikely Pyxis is associated with either system. We examine other Milky Way satellites for possible association using the orbit, eccentricity, metallicity, and age as constraints and find no likely matches in satellites down to the mass of Leo II. We propose that Pyxis probably originated in an unknown galaxy, which today is fully disrupted. Assuming that Pyxis is bound and not on a first approach, we derive a 68% lower limit on the mass of the Milky Way of 0.76*10^12 M_sun.
We revisit the massive isolated elliptical galaxy / fossil group NGC 6482 for which previous X-ray studies of a modest Chandra observation obtained a very uncertain, but also possibly very high, halo concentration. We present new measurements of the hot gas surface brightness, temperature, and iron abundance using the modest Chandra observation and a previously unpublished Suzaku observation, the latter of which allows measurements of the gas properties to be extended out to ~r_2500. By constructing hydrostatic equilibrium models of the gas with separate components for the gas, BCG stellar mass, and the dark matter (DM), we measure c_200 = 32.2 +/- 7.1 and M_200 = (4.5 +/- 0.6 x 10^12 M_sun using an NFW DM profile. For a halo of this mass, c_200 exceeds the mean value (7.1) expected for relaxed LCDM halos by $3.5 \sigma$ in terms of the observational error, and by $6 \sigma$ considering the intrinsic scatter in the LCDM c-M relation, which situates NGC 6482 as the most extreme outlier known for a fossil system. We explored several variants of adiabatic contraction (AC) models and, while the AC models provide fits of the same quality as the un-contracted models, they do have the following advantages: (1) smaller c_200 that is less of an outlier in the LCDM c-M relation, and (2) baryon fractions that agree better with the mean cosmic value. While the standard AC prescriptions yield a BCG stellar mass that is uncomfortably small compared to results from stellar population synthesis (SPS) models, a weaker AC variant that artificially shuts off cooling and star formation at z=2 yields the same stellar mass as the un-contracted models. For these reasons, we believe our X-ray analysis prefers this weaker AC variant applied to either an NFW or Einasto DM halo. Finally, the BCG stellar mass strongly favors SPS models with a Chabrier or Kroupa IMF over a Salpeter IMF. (Abridged)
Interstellar iron in the form of metallic iron nanoparticles may constitute a component of the interstellar dust. We compute the stability of iron nanoparticles to sublimation in the interstellar radiation field, finding that iron clusters can persist down to a radius of $\simeq 4.5\,$\AA, and perhaps smaller. We employ laboratory data on small iron clusters to compute the photoelectric yields as a function of grain size and the resulting grain charge distribution in various interstellar environments, finding that iron nanoparticles can acquire negative charges particularly in regions with high gas temperatures and ionization fractions. If $\gtrsim 10\%$ of the interstellar iron is in the form of ultrasmall iron clusters, the photoelectric heating rate from dust may be increased by up to tens of percent relative to dust models with only carbonaceous and silicate grains.
Determining elemental abundances of bulge stars can, via chemical evolution modeling, help to understand the formation and evolution of the bulge. Recently there have been claims both for and against the bulge having a different [$\alpha$/Fe] vs. [Fe/H]-trend as compared to the local thick disk possibly meaning a faster, or at least different, formation time scale of the bulge as compared to the local thick disk. We aim to determine the abundances of oxygen, magnesium, calcium, and titanium in a sample of 46 bulge K-giants, 35 of which have been analyzed for oxygen and magnesium in previous works, and compare them to homogeneously determined elemental abundances of a local disk sample of 291 K-giants. We use spectral synthesis to determine both the stellar parameters as well as the elemental abundances of the bulge stars analyzed here. The method is exactly the same as was used for analyzing the comparison sample of 291 local K-giants in Paper I of this series. Compared to the previous analysis of the 35 stars in our sample, we find lower [Mg/Fe] for [Fe/H]>-0.5, and therefore contradict the conclusion about a declining [O/Mg] for increasing [Fe/H]. We instead see a constant [O/Mg] over all the observed [Fe/H] in the bulge. Furthermore, we find no evidence for a different behavior of the alpha-iron trends in the bulge as compared to the local thick disk from our two samples.
We investigate the clustering properties of 45441 radio-quiet quasars (RQQs) and 3493 radio-loud quasars (RLQs) drawn from a joint use of the Sloan Digital Sky Survey (SDSS) and Faint Images of the Radio Sky at 20 cm (FIRST) surveys in the range $0.3<z<2.3$. This large spectroscopic quasar sample allow us to investigate the clustering signal dependence on radio-loudness and black hole (BH) virial mass. We find that RLQs are clustered more strongly than RQQs in all the redshift bins considered. We find a real-space correlation length of $r_{0}=6.59_{-0.24}^{+0.33}\,h^{-1}\,\textrm{Mpc}$ and $r_{0}=10.95_{-1.58}^{+1.22}\,h^{-1}\,\textrm{Mpc}$ {\normalsize{}for} RQQs and RLQs, respectively, for the full redshift range. This implies that RLQs are found in more massive host haloes than RQQs in our samples, with mean host halo masses of $\sim4.9\times10^{13}\,h^{-1}\,M_{\odot}$ and $\sim1.9\times10^{12}\,h^{-1}\,M_{\odot}$, respectively. Comparison with clustering studies of different radio source samples indicates that this mass scale of $\gtrsim1\times10^{13}\,h^{-1}\,M_{\odot}$ is characteristic for the bright radio-population, which corresponds to the typical mass of galaxy groups and galaxy clusters. The similarity we find in correlation lengths and host halo masses for RLQs, radio galaxies and flat-spectrum radio quasars agrees with orientation-driven unification models. Additionally, the clustering signal shows a dependence on black hole (BH) mass, with the quasars powered by the most massive BHs clustering more strongly than quasars having less massive BHs. We suggest that the current virial BH mass estimates may be a valid BH proxies for studying quasar clustering. We compare our results to a previous theoretical model that assumes that quasar activity
Extremely wide binary stars represent ideal systems to probe Newtonian dynamics in the low acceleration regimes (<10e-10 m/s/s) typical of the external regions of galaxies. Here we present a study of 60 alleged wide binary stars with projected separation ranging from 0.004 to 1 pc, probing gravitational accelerations well below the limit were dark matter or modified dynamics theories set in. Radial velocities with accuracy ~100 m/s were obtained for each star, in order to constrain their orbital velocity, that, together with proper motion data, can distinguish bound from unbound systems. It was found that about half of the observed pairs do have velocity in the expected range for bound systems, out to the largest separations probed here. In particular, we identified five pairs with projected separation >0.15 pc that are useful for the proposed test. While it would be premature to draw any conclusion about the validity of Newtonian dynamics at these low accelerations, our main result is that very wide binary stars seem to exist in the harsh environment of the solar neighborhood. This could provide a tool to test Newtonian dynamics versus modified dynamics theories in the low acceleration conditions typical of galaxies. In the near future the GAIA satellite will provide data to increase significantly the number of wide pairs that, with the appropriate follow up spectroscopic observations, will allow the implementation of this experiment with unprecedented accuracy.
The correlation between the jet power and accretion disk luminosity is investigated and analyzed with our model for 7 samples of low luminosity active galactic nuclei (LLAGNs). The main results are: (1) the power-law correlation index ($P_{jet} \propto L_{disk}^{\mu}$) typically ranges $\mu=0.4-0.7$ for the LLAGN samples, and there is a hint of steep index for the LLAGN sample which hosted by a high fraction of elliptical galaxies, and there are no significant correlation between the $\mu$ and the LLAGN types (Seyfert, LINER); (2) for $\mu \approx$1, as noted in Liu et al., the accretion disk dominates the jet power and the black hole (BH) spin is not important, for the LLAGN samples studied in this paper we find that the $\mu$ is significantly less than unity, implying that BH spin may play a significant role in the jet power of LLAGNs; (3) the BH spin-jet power is negatively correlated with the BH mass in our model, which means a high spin-jet efficiency in the `low' BH-mass LLAGNs; (4) an anti-correlation between radio loudness and disk luminosity is found, which is apparently due to the flatter power-law index in the jet-disk correlation of the LLAGNs, and the radio loudness can be higher in the LLAGNs than in luminous AGNs/quasars when the BH spin-jet power is comparable to or dominate over the accretion-jet power in the LLAGNs. The high radio-core dominance of the LLAGNs is also discussed.
Context. Infrared dark clouds (IRDCs) are ubiquitous in the Milky Way, yet
they play a crucial role in breeding newly-formed stars.
Aims. In order to further understand the dynamics, chemistry, and evolution
of IRDCs, we carried out multi-wavelength observations towards a small sample.
Methods. We performed new observations with the IRAM 30 m and CSO 10.4 m
telescopes, with tracers ${\rm HCO^+}$, HCN, ${\rm N_2H^+}$, ${\rm C^{18}O}$,
DCO$^+$, SiO, and DCN towards six IRDCs G031.97+00.07, G033.69-00.01,
G034.43+00.24, G035.39-00.33, G038.95-00.47, and G053.11+00.05.
Results. We investigated 44 cores including 37 cores reported in previous
work and 7 newly-identified cores. Towards the dense cores, we detected 6
DCO$^+$, and 5 DCN lines. Using pixel-by-pixel spectral energy distribution
(SED) fits of the \textit{Herschel} 70 to 500 $\mu$m, we obtain dust
temperature and column density distributions of the IRDCs. We find that ${\rm
N_2H^+}$ emission has a strong correlation with the dust temperature and column
density distributions, while the worst is ${\rm C^{18}O}$. It is suggested that
${\rm N_2H^+}$ is indeed a good tracer in very dense condition, however an
unreliable one is ${\rm C^{18}O}$, which has a relatively low critical density
and is vulnerable to freeze out onto the surface of cold dust grains. The
dynamics within IRDCs is active with infall, outflow, and collapse, the spectra
are abundant especially in deuterium species.
Conclusions. We observe many blueshifted and redshifted profiles,
respectively, with ${\rm HCO^+}$ and ${\rm C^{18}O}$ towards the same core.
This case can be well explained by model "envelope expansion with core collapse
(EECC)".
We report on the diversity in quasar spectra from the Baryon Oscillation Spectroscopic Survey. After filtering the spectra to mitigate selection effects and Malmquist bias associated with a nearly flux-limited sample, we create high signal-to-noise ratio composite spectra from 58,656 quasars (2.1 \le z \le 3.5), binned by luminosity, spectral index, and redshift. With these composite spectra, we confirm the traditional Baldwin effect (BE, i.e., the anticorrelation of C IV equivalent width (EW) and luminosity) that follows the relation W_\lambda \propto L^{\beta_w} with slope \beta_w = -0.35 \pm 0.004, -0.35 \pm 0.005, and -0.41 \pm 0.005 for z = 2.25, 2.46, and 2.84, respectively. In addition to the redshift evolution in the slope of the BE, we find redshift evolution in average quasar spectral features at fixed luminosity. The spectroscopic signature of the redshift evolution is correlated at 98% with the signature of varying luminosity, indicating that they arise from the same physical mechanism. At a fixed luminosity, the average C IV FWHM decreases with increasing redshift and is anti-correlated with C IV EW. The spectroscopic signature associated with C IV FWHM suggests that the trends in luminosity and redshift are likely caused by a superposition of effects that are related to black hole mass and Eddington ratio. The redshift evolution is the consequence of a changing balance between these two quantities as quasars evolve toward a population with lower typical accretion rates at a given black hole mass.
We report an early science discovery of the CO(1-0) emission line in the collisional ring galaxy, VII Zw466, using the Redshift Search Receiver instrument on the Large Millimeter Telescope Alfonso Serrano.The apparent molecular-to-atomic gas ratio either places the ISM of VII Zw466 in the HI-dominated regime or implies a large quantity of CO-dark molecular gas, given its high star formation rate. The molecular gas densities and star formation rate densities of VII Zw466 are consistent with the standard Kennicutt-Schmidt star formation law even though we find this galaxy to be H2-deficient. The choice of CO-to-H2 conversion factors cannot explain the apparent H2 deficiency in its entirety. Hence, we find that the collisional ring galaxy, VII Zw466, is either largely deficient in both H2 and HI or contains a large mass of CO-dark gas. A low molecular gas fraction could be due to the enhancement of feedback processes from previous episodes of star formation as a result of the star-forming ISM being confined to the ring. We conclude that collisional ring galaxy formation is an extreme form of galaxy interaction that triggers a strong galactic-wide burst of star formation that may provide immediate negative feedback towards subsequent episodes of star formation---resulting in a short-lived star formation history or, at least, the appearance of a molecular gas deficit.
We present a novel interpretation of the previously puzzling different behaviours of stellar populations of the Milky Way's bulge. We first show, by means of pure N-body simulations, that initially co-spatial stellar populations with different in-plane random motions separate when a bar forms. The radially cooler populations form a strong bar, and are vertically thin and peanut-shaped, while the hotter populations form a weaker bar and become a vertically thicker box. We demonstrate that it is the radial, not the vertical, velocity dispersion that drives this evolution. Assuming that early stellar discs heat rapidly as they form, then both the in-plane and vertical random motions correlate with stellar age and chemistry, leading to different density distributions for metal-rich and metal-poor stars. We then use a high resolution simulation, in which all stars form out of gas, to demonstrate that this is what happens. When we apply these results to the Milky Way we show that a very broad range of observed trends for ages, densities, kinematics, and chemistries, that have been presented as evidence for contradictory paths to the formation of the bulge, are in fact consistent with a bulge which formed from a continuum of disc stellar populations which were kinematically separated by the bar. For the first time we are able to account for the bulge's main trends via a model in which the bulge formed completely in situ. Since the model is generic, we also predict the general appearance of stellar population maps of external edge-on galaxies.
Using 25 years of data from uninterrupted monitoring of stellar orbits in the Galactic Center, we present an update of the main results from this unique data set: A measurement of mass of and distance to SgrA*. Our progress is not only due to the eight year increase in time base, but also due to the improved definition of the coordinate system. The star S2 continues to yield the best constraints on the mass of and distance to SgrA*; the statistical errors of 0.13 x 10^6 M_sun and 0.12 kpc have halved compared to the previous study. The S2 orbit fit is robust and does not need any prior information. Using coordinate system priors, also the star S1 yields tight constraints on mass and distance. For a combined orbit fit, we use 17 stars, which yields our current best estimates for mass and distance: M = 4.28 +/- 0.10|stat. +/. 0.21|sys. x 10^6 M_sun and R_0 = 8.32 +/- 0.07|stat. +/- 0.14|sys. kpc. These numbers are in agreement with the recent determination of R_0 from the statistical cluster parallax. The positions of the mass, of the near-infrared flares from SgrA* and of the radio source SgrA* agree to within 1mas. In total, we have determined orbits for 40 stars so far, a sample which consists of 32 stars with randomly oriented orbits and a thermal eccentricity distribution, plus eight stars for which we can explicitly show that they are members of the clockwise disk of young stars, and which have lower eccentricity orbits.
Our goal is to study the evolution of the $B-$band luminosity function (LF) since $z=1$ using ALHAMBRA data. We used the photometric redshift and the $I-$band selection magnitude probability distribution functions (PDFs) of those ALHAMBRA galaxies with $I\leq24$ mag to compute the posterior LF. We statistically studied quiescent and star-forming galaxies using the template information encoded in the PDFs. The LF covariance matrix in redshift-magnitude-galaxy type space was computed, including the cosmic variance. That was estimated from the intrinsic dispersion of the LF measurements in the 48 ALHAMBRA sub-fields. The uncertainty due to the photometric redshift prior is also included in our analysis. We modelled the LF with a redshift-dependent Schechter function affected by the same selection effects than the data. The measured ALHAMBRA LF at $0.2\leq z<1$ and the evolving Schechter parameters both for quiescent and star-forming galaxies agree with previous results in the literature. The estimated redshift evolution of $M_B^* \propto Qz$ is $Q_{\rm SF}=-1.03\pm0.08$ and $Q_{\rm Q}=-0.80\pm0.08$, and of $\log \phi^* \propto Pz$ is $P_{\rm SF}=-0.01\pm0.03$ and $P_{\rm Q}=-0.41\pm0.05$. The measured faint-end slopes are $\alpha_{\rm SF}=-1.29\pm0.02$ and $\alpha_{\rm Q}=-0.53\pm0.04$. We find a significant population of faint quiescent galaxies, modelled by a second Schechter function with slope $\beta=-1.31\pm0.11$. We find a factor $2.55\pm0.14$ decrease in the luminosity density $j_B$ of star-forming galaxies, and a factor $1.25\pm0.16$ increase in the $j_B$ of quiescent ones since $z=1$, confirming the continuous build-up of the quiescent population with cosmic time. The contribution of the faint quiescent population to $j_B$ increases from 3% at $z=1$ to 6% at $z=0$. The developed methodology will be applied to future multi-filter surveys such as J-PAS.
We investigate the simultaneous triggering of active galactic nuclei (AGN) in merging galaxies, using a large suite of high-resolution hydrodynamical simulations. We compute dual-AGN observability time-scales using bolometric, X-ray, and Eddington-ratio thresholds, confirming that dual activity from supermassive black holes (BHs) is generally higher at late pericentric passages, before a merger remnant has formed, especially at high luminosities. For typical minor and major mergers, dual activity lasts ~20-70 and ~100-160 Myr, respectively. We also explore the effects of X-ray obscuration from gas, finding that the dual-AGN time decreases at most by a factor of ~2, and of contamination from star formation. Using projected separations and velocity differences rather than three-dimensional quantities can decrease the dual-AGN time-scales by up to ~4, and we apply filters which mimic current observational-resolution limitations. In agreement with observations, we find that, for a sample of major mergers hosting at least one AGN, ~20 per cent of them should harbour dual AGN. We quantify the effects of merger mass ratio (0.1 to 1), geometry (coplanar, prograde, retrograde, and inclined), disc gas fraction, and BH properties, finding that the mass ratio is the most important factor, with the difference between minor and major mergers varying between factors of a few to orders of magnitude, depending on the luminosity and filter used. We also find that a deep imaging survey does not need very high angular resolution, whereas a shallow survey requires it.
We present images and spectral energy distributions (SEDs) of massive young stellar objects (YSOs) in three star-forming H II regions of the Large Magellanic Cloud: N159A, N159 Papillon, and N160. We use photometry from SOFIA/FORCAST at 25.3--37.1 um to constrain model fits to the SEDs and determine luminosities, ages, and dust content of the embedded YSOs and their local environments. By placing these sources on mid-infrared color-magnitude and color-color diagrams, we analyze their dust properties and consider their evolutionary status. Since each object in the FORCAST images has an obvious bright near-infrared counterpart in Spitzer Space Telescope images, we do not find any evidence for new, very cool, previously-undiscovered Class 0 YSOs. Additionally, based on its mid-infrared colors and model parameters, N159A is younger than N160 and the Papillon. The nature of the first extragalactic protostars in N159, P1 and P2, is also discussed.
We present high signal-to-noise galaxy-galaxy lensing measurements of the BOSS CMASS sample using 250 square degrees of weak lensing data from CFHTLenS and CS82. We compare this signal with predictions from mock catalogs trained to match observables including the stellar mass function and the projected and two dimensional clustering of CMASS. We show that the clustering of CMASS, together with standard models of the galaxy-halo connection, robustly predicts a lensing signal that is 20-40% larger than observed. Detailed tests show that our results are robust to a variety of systematic effects. Lowering the value of $S_{\rm 8}=\sigma_{\rm 8} \sqrt{\Omega_{\rm m}/0.3}$ compared to Planck2015 reconciles the lensing with clustering. However, given the scale of our measurement ($r<10$ $h^{-1}$ Mpc), other effects may also be at play and need to be taken into consideration. We explore the impact of baryon physics, assembly bias, massive neutrinos, and modifications to general relativity on $\Delta\Sigma$ and show that several of these effects may be non-negligible given the precision of our measurement. Disentangling cosmological effects from the details of the galaxy-halo connection, the effects of baryons, and massive neutrinos, is the next challenge facing joint lensing and clustering analyses. This is especially true in the context of large galaxy samples from Baryon Acoustic Oscillation surveys with precise measurements but complex selection functions.
This paper presents a review of the characteristics of the multiple stellar populations observed in globular clusters, and of their possible origin. The current theoretical issues and the many open questions are discussed.
The final step of the water formation network on interstellar grain surfaces starting from the H + O$_2$ route is the reaction between H and H$_2$O$_2$. This reaction is known to have a high activation energy and therefore at low temperatures it can only proceed via tunneling. To date, however, no rate constants are available at temperatures below 200 K. In this work, we use instanton theory to compute rate constants for the title reaction with and without isotopic substitutions down to temperatures of 50 K. The calculations are based on density functional theory, with additional benchmarks for the activation energy using unrestricted single-reference and multireference coupled-cluster single-point energies. Gas-phase bimolecular rate constants are calculated and compared with available experimental data not only for H + H$_2$O$_2$ $\rightarrow$ H$_2$O + OH, but also for H + H$_2$O$_2$ $\rightarrow$ H$_2$ + HO$_2$. We find a branching ratio where the title reaction is favored by at least two orders of magnitude at 114 K. In the interstellar medium this reaction predominantly occurs on water surfaces, which increases the probability that the two reactants meet. To mimic this one, two, or three spectator H2O molecules are added to the system. Eley-Rideal bimolecular and Langmuir-Hinshelwood unimolecular rate constants are presented here. The kinetic isotope effects for the various cases are compared to experimental data as well as to expressions commonly used in astrochemical models. Both the rectangular barrier and the Eckart approximations lead to errors of about an order of magnitude. Finally, fits of the rate constants are provided as input for astrochemical models.
The emergence of cosmic structure is commonly considered one of the most complex phenomena in Nature. However, this complexity has never been defined nor measured in a quantitative and objective way. In this work we propose a method to measure the information content of cosmic structure and to quantify the complexity that emerges from it, based on Information Theory. The emergence of complex evolutionary patterns is studied with a statistical symbolic analysis of the datastream produced by state-of-the-art cosmological simulations of forming galaxy clusters. This powerful approach allows us to measure how many bits of information are necessary to predict the evolution of energy fields in a statistical way, and it offers a simple way to quantify when, where and how the cosmic gas behaves in complex ways. The most complex behaviors are found in the peripheral regions of galaxy clusters, where supersonic flows drive shocks and large energy fluctuations over a few tens of million years. Describing the evolution of magnetic energy requires at least a twice as large amount of bits than for the other energy fields. When radiative cooling and feedback from galaxy formation are considered, the cosmic gas is overall found to double its degree of complexity. In the future, Cosmic Information Theory can significantly increase our understanding of the emergence of cosmic structure as it represents an innovative framework to design and analyze complex simulations of the Universe in a simple, yet powerful way.
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We present the first determination of the galaxy luminosity function (LF) at z~4, 5, 6 and 7 in the rest-frame optical at lambda_rest~900 nm (z' band). The rest-frame optical light traces the content in low-mass evolved stars (~stellar mass - Mstar), minimizing potential biases affecting measurements of Mstar: it is less affected by nebular line emission contamination, it is less sensitive to dust attenuation models, its measurement does not rely on stellar population models, and it can be probed up to z~8 through Spitzer/IRAC. Our analysis leverages the unique full depth Spitzer/IRAC 3.6um-to-8.0um data over the CANDELS/GOODS-N, CANDELS/GOODS-S and COSMOS/UltraVISTA fields. We find that at absolute magnitudes M_z' fainter than >-23 mag, M_z' linearly correlates with M_UV,1600. At brighter M_z', M_UV,1600 presents a turnover, suggesting that the stellar mass-to-light ratio Mstar/L_UV,1600 could be characterised by a very broad range of values at high stellar masses. Median-stacking analysis recovers a Mstar/L_z' roughly independent on M_z' for M_z'>-23 mag, but exponentially increasing at brighter magnitudes. We find that the evolution of the LF marginally prefers a pure evolution in luminosity over a pure evolution in density, with the characteristic luminosity decreasing by a factor ~5x between z~4 and z~7. Direct application of the recovered Mstar/L_z' generates stellar mass functions consistent with average measurements from the literature. Measurements of the stellar-to-halo mass ratio at fixed cumulative number density show that it is roughly constant with redshift for Mh>10^12Msun. This is also supported by the fact that the evolution of the LF at 4<z<7 can be accounted for by a rigid displacement in luminosity corresponding to the evolution of the halo mass from abundance matching.
Distance uncertainties plague our understanding of the physical scales relevant to the physics of star formation in extragalactic studies. The planetary nebulae luminosity function (PNLF) is one of very few techniques that can provide distance estimates to within ~10%, however it requires a planetary nebula (PN) sample that is uncontaminated by other ionizing sources. We employ optical IFU spectroscopy using MUSE on the VLT to measure [OIII] line fluxes for sources unresolved on 50 pc scales within the central star-forming galaxy disk of NGC 628. We use diagnostic line ratios to identify 62 PNe, 30 supernova remnants and 87 HII regions within our fields. Using the 36 brightest PNe we determine a new PNLF distance modulus of 29.91^{+0.08}_{-0.13} mag (9.59^{+0.35}_{-0.57} Mpc), in good agreement with literature values but significantly larger than the previously reported PNLF distance. We are able to explain the discrepancy and recover the previous result when we reintroduce SNR contaminants to our sample. This demonstrates the power of full spectral information over narrowband imaging in isolating PNe. Given our limited spatial coverage within the galaxy, we show that this technique can be used to refine distance estimates even when IFU observations cover only a fraction of a galaxy disk.
We update our recently published model for GAlaxy Evolution and Assembly (GAEA), to include a self-consistent treatment of the partition of cold gas in atomic and molecular hydrogen. Our model provides significant improvements with respect to previous ones used for similar studies. In particular, GAEA (i) includes a sophisticated chemical enrichment scheme accounting for non-instantaneous recycling of gas, metals, and energy; (ii) reproduces the measured evolution of the galaxy stellar mass function; (iii) reproduces the observed correlation between galaxy stellar mass and gas metallicity at different redshifts. These are important prerequisites for models considering a metallicity dependent efficiency of molecular gas formation. We also update our model for disk sizes and show that model predictions are in nice agreement with observational estimates for the gas, stellar and star forming disks at different cosmic epochs. We analyse the influence of different star formation laws including empirical relations based on the hydrostatic pressure of the disk, analytic models, and prescriptions derived from detailed hydrodynamical simulations. We find that modifying the star formation law does not affect significantly the global properties of model galaxies, neither their distributions. The only quantity showing significant deviations in different models is the cosmic molecular-to-atomic hydrogen ratio, particularly at high redshift. Unfortunately, however, this quantity also depends strongly on the modelling adopted for additional physical processes. Low mass galaxies at high redshift can provide useful constraints on the physical processes affecting star formation, as self-regulation has not yet washed out differences imprinted at early times.
We present a pilot study on the nearby massive barred galaxy NGC 1291, in which we use dynamical modelling to constrain the disc mass-to-light ratio (M/L), thus breaking the degeneracy between the baryonic and dark matter in its central regions. We use the gas, specifically the morphology of the dust lanes on the leading side of the bar, as a tracer of the underlying gravitational potential. We run a large number of hydrodynamic gas response simulations, in potentials obtained directly from near-infrared images of the galaxy, which have three free parameters: the M/L, the bar pattern speed and the height function. We explore the three-dimensional parameter space, by comparing the morphology of the shocks created in the gas response simulations with those of the observed dust lanes, and find the best-fitting models; these suggest that the M/L of NGC 1291 agrees with that predicted by stellar population synthesis models in the near-infrared ($\approx$0.6\,$M_{\odot}/L_{\odot}$), which leads to a borderline maximum disc for this galaxy. Furthermore, we find that the bar rotates fast, with a corotation radius which is $\leq$ 1.4 times the bar length.
Two modes of star formation are involved to explain the origin of young stars near Sgr A*. One is a disk-based mode, which explains the disk of stars orbiting Sgr A*. The other is the standard cloud-based mode observed in the Galactic disk. We discuss each of these modes of star formation and apply these ideas to the inner few parsecs of Sgr A*. In particular, we focus on the latter mode in more detail. We also discuss how the tidal force exerted by the nuclear cluster makes the Roche density approaching zero and contributes to the collapse of molecular clouds located tens of parsecs away from Sgr A*.
Bulges of edge-on galaxies are often boxy/peanut-shaped (B/PS), and unsharp masks reveal the presence of an X shape. Simulations show that these shapes can be produced by dynamical processes driven by a bar which vertically thickens the centre. In the Milky Way, which contains such a B/PS bulge, the X-shaped structure is traced by the metal-rich stars but not by the metal-poor ones. Recently Debattista et al. (2016) interpreted this property as a result of the varying effect of the bar on stellar populations with different starting kinematics. This kinematic fractionation model predicts that cooler populations at the time of bar formation go on to trace the X shape, whereas hotter populations are more uniformly distributed. As this prediction is not specific to the Milky Way, we test it with MUSE observations of the B/PS bulge in the nearby galaxy NGC 4710. We show that the metallicity map is more peanut-shaped than the density distribution itself, in good agreement with the prediction. This result indicates that the X-shaped structure in B/PS bulges is formed of relatively metal-rich stars that have been vertically redistributed by the bar, whereas the metal-poor stars have a more uniform, box-shaped distribution.
We analyze the evolution of oxygen abundance radial gradients resulting from our chemical evolution models calculated with different prescriptions for the star formation rate (SFR) and for the gas infall rate, in order to assess their respective roles in shaping gradients. We also compare with cosmological simulations and confront all with recent observational datasets, in particular with abundances inferred from planetary nebulae. We demonstrate the critical importance in isolating the specific radial range over which a gradient is measured, in order for their temporal evolution to be useful indicators of disk growth with redshift.
We report H$_2$O maser line observations of the bright-rimmed globule IC 1396 N using a ground-space interferometer with the 10-m RadioAstron radio telescope as the space-based element. The source was not detected on projected baselines >2.3 Earth diameters, which indicates a lower limit on the maser size of L >0.03 AU and an upper limit on the brightness temperature of 6.25 x 10$^{12}$ K. Positions and flux densities of maser spots were determined by fringe rate mapping. Multiple low-velocity features from -4.5 km/s to +0.7 km/s are seen, and two high-velocity features of V$_{LSR}$=-9.4 km/s and +4.4 km/s are found at projected distances of 157 AU and 70 AU, respectively, from the strongest low-velocity feature at V$_{LSR}$=$\sim$0.3 km/s. Maser components from the central part of the spectrum fall into four velocity groups but into three spatial groups. Three spatial groups of low-velocity features detected in the 2014 observations are arranged in a linear structure about 200 AU in length. Two of these groups were not detected in 1996 and possibly are jets which formed between 1996 and 2014. The putative jet seems to have changed direction in 18 years, which we explain by the precession of the jet under the influence of the gravity of material surrounding the globule. The jet collimation can be provided by a circumstellar protoplanetary disk. There is a straight line orientation in the V$_{LSR}$-Right Ascension diagram between the jet and the maser group at V$_{LSR}$=$\sim$0.3 km/s. However, the central group with the same position but at the velocity V$_{LSR}$$\sim$-3.4 km/s falls on a straight line between two high-velocity components detected in 2014. Comparison of the low-velocity positions from 2014 and 1996, based on the same diagram, shows that the majority of the masers maintain their positions near the central velocity V$_{LSR}$=$\sim$0.3 km/s during the 18 year period.
The effective temperature (Teff) of the radiation field of the ionizing star(s) of a large sample of extragalactic HII regions was estimated using the R= log([OII](3727)/[OIII]5007) index. We used a grid of photoionization models to calibrate the Teff-R relation finding that it has a strong dependence with the ionizing parameter while it shows a weak direct dependence with the metallicity (variations in Z imply variations in U) of both the stellar atmosphere of the ionizing star and the gas phase of the HII region. Since the R index varies slightly with the Teff for values larger than 40 kK, the R index can be used to derive the Teff in 30-40 kK range. A large fraction of the ionization parameter variation is due to differences in the temperature of the ionizing stars and then the use of the (relatively) low Teff dependent S2=[S II](6717+31)/Ha emission-line ratio to derive the ionization parameter is preferable over others in the literature. We propose linear metallicity dependent relationships between S2 and U. Teff and metallicity estimations for a sample of 865 HII regions, whose emission-line intensities were compiled from the literature, do not show any Teff-Z correlation. On the other hand it seems to be hints of the presence of an anti-correlation between Teff-U. We found that the majority of the studied HII regions (87%) present Teff values in the range between 37 and 40 kK, with an average value of 38.5 kK. We also studied the variation of Teff as a function of the galactocentric distance for 14 spiral galaxies. Our results are in agreement with the idea of the existence of positive Teff gradients along the disk of spiral galaxies.
We analyse the structure and kinematics of ionized gas in the vicinity of the ultraluminous X-ray source (ULX) HoII X-1 in the Holmberg II galaxy using observational data obtained with a scanning Fabry-Perot interferometer in the H$\alpha$, [SII] and [OIII] emission lines at the Russian 6-m telescope. Decomposition of the line profiles allows us to identify the broad component of emission lines caused by the ULX action. We found evidence of an expanding superbubble around the young star cluster located in the studied region. We conclude that the blue-shifted 'arc' around the ULX observed in the line-of-sight velocity field may correspond to a bow shock caused by the ULX movement from that nearby young star cluster. If this interpretation is correct, it will be the first kinematic evidence of ULX's escape from their parent star clusters.
The dynamical processes involving stellar-remnant black holes (BH) in stellar clusters has always drawn attention due to the BHs' potential in a number of astrophysical phenomena, especially the dynamical formation of binary black holes (BBH), which would potentially coalesce via radiation of gravitational waves (GW). This study presents a preliminary set of evolutionary models of compact stellar clusters with initial masses ranging over $1.0\times10^4M_\odot-5.0\times10^4M_\odot$, and half-mass radius of 2 pc or 1 pc, that is typical for young massive and starburst clusters. They have metallicities between $0.05Z_\odot-Z_\odot$. Including contemporary schemes for stellar wind and remnant-formation, such model clusters are evolved, for the first time, using the state-of-the-art direct N-body evolution program NBODY7, until their dissolution or at least for 10 Gyr. That way, a self-regulatory behaviour in the effects of dynamical interactions among the BHs, especially while heating and expanding the cluster and self-depleting the BHs, is demonstrated. The BBH mergers obtained here show a prominence in triple-mediated mergers while being bound to the clusters, compared to those occurring among the BBHs that are dynamically ejected from the clusters. This is in contrast with earlier N-body computations and also with recent Monte-Carlo method based ones. A broader mass spectrum of BHs and ejection of BBHs generally of wider orbits and in lower numbers, for the cluster masses explored here, might cause this which is yet to be fully understood. Among the BBH coalescences obtained here, there are ones that resemble the detected GW151226, LVT151012, and GW150914 events and also ones which are even more massive. A preliminary estimate suggests few 10s - 100s of BBH coalescences per year, originating due to dynamics in stellar clusters, that can be detected by the LIGO at its design sensitivity.
We perform a large suite of $N=4$ numerical scattering experiments between two identical binaries consisting of identical point particles in a (continuous) background potential. For investigative purposes, albeit without loss of generality, we assume that the potential corresponds to a uniform (natal or star-forming) gas medium. We explore a range of constant gas densities, from $n=10~ {\rm cm}^{-3}$ to $10^{5}~ {\rm cm}^{-3}$. These densities are relevant for various astrophysical environments, including molecular clouds (i.e., star-forming regions) and denser, fragmented cores within these clouds. Our primary goal is to characterize the effects of the background potential on the subsequent stellar dynamics. We consider the outcome probabilities as well as the properties of any binaries formed during the binary-binary encounters, such as the distributions of binary binding energies and eccentricities. We also present the final velocity distributions of the ejected single stars. The background potential has two important effects on the stellar dynamics: 1) The potential acts to reset the zero-point of the total system energy, which in turn affects the types and properties of the products of the encounter; 2) For higher $n$ and weakly bound systems (i.e., large semimajor axes), the stellar dynamics are significantly affected when stars become trapped in the potential, oscillating around the system centre of mass (CM). This, in turn, increases the number of scattering events between stars (single, binary or triple) near the CM and makes it harder for single stars to escape to infinity. This ultimately leads to the preferential ionization of triples and wide binaries and the survival of compact binaries, with the single stars escaping at very high ejection velocities.
We study formation and long-term evolution of a circumstellar disk in a collapsing molecular cloud core using a resistive magnetohydrodynamic simulation. While the formed circumstellar disk is initially small, it grows as accretion continues and its radius becomes as large as 200 AUs toward the end of the Class-I phase. A pair of grand-design spiral arms form due to gravitational instability in the disk, and they transfer angular momentum in the highly resistive disk. Although the spiral arms disappear in a few rotations as expected in a classical theory, new spiral arms form recurrently as the disk soon becomes unstable again by gas accretion. Such recurrent spiral arms persist throughout the Class-0 and I phase. We then perform synthetic observations and compare our model with a recent high-resolution observation of a young stellar object Elias 2-27, whose circumstellar disk has grand design spiral arms. We find an excellent agreement between our theoretical model and the observation. Our model suggests that the grand design spiral arms around Elias 2-27 are consistent with material arms formed by gravitational instability. It also implies that the age of Elias 2-27 can be younger than the previous estimate.
The Type~Ia supernova (SN~Ia) 2016coj in NGC 4125 (redshift $z=0.004523$) was discovered by the Lick Observatory Supernova Search 4.9 days after the fitted first-light time (FFLT; 11.1 days before $B$-band maximum). Our first detection (pre-discovery) is merely $0.6\pm0.5$ day after the FFLT, making SN 2016coj one of the earliest known detections of a SN Ia. A spectrum was taken only 3.7 hr after discovery (5.0 days after the FFLT) and classified as a normal SN Ia. We performed high-quality photometry, low- and high-resolution spectroscopy, and spectropolarimetry, finding that SN 2016coj is a spectroscopically normal SN Ia, but with a high velocity of \ion{Si}{2} $\lambda$6355 ($\sim 12,600$\,\kms\ around peak brightness). The \ion{Si}{2} $\lambda$6355 velocity evolution can be well fit by a broken-power-law function for up to a month after the FFLT. SN 2016coj has a normal peak luminosity ($M_B \approx -18.9 \pm 0.2$ mag), and it reaches a $B$-band maximum \about16.0~d after the FFLT. We estimate there to be low host-galaxy extinction based on the absence of Na~I~D absorption lines in our low- and high-resolution spectra. The spectropolarimetric data exhibit weak polarization in the continuum, but the \ion{Si}{2} line polarization is quite strong ($\sim 0.9\% \pm 0.1\%$) at peak brightness.
Supermassive stars (SMS; ~ 10^5 M_sun) formed from metal-free gas in the early Universe attract attention as progenitors of supermassive black holes observed at high redshifts. To form SMSs by accretion, central protostars must accrete at as high rates as ~ 0.1-1 M_sun/yr. Such protostars have very extended structures with bloated envelopes, like super-giant stars, and are called super-giant protostars (SGPSs). Under the assumption of hydrostatic equilibrium, SGPSs have density inverted layers, where the luminosity becomes locally super-Eddington, near the surface. If the envelope matter is allowed to flow out, however, a stellar wind could be launched and hinder the accretion growth of SGPSs before reaching the supermassive regime. We examine whether radiation-driven winds are launched from SGPSs by constructing steady and spherically symmetric wind solutions. We find that the wind velocity does not reach the escape velocity in any case considered. This is because once the temperature falls below ~ 10^4 K, the opacity plummet drastically owing to the recombination of hydrogen and the acceleration ceases suddenly. This indicates that, in realistic non-steady cases, even if outflows are launched from the surface of SGPSs, they would fall back again. Such a "wind" does not result in net mass loss and does not prevent the growth of SGPSs. In conclusion, SGPSs will grow to SMSs and eventually collapse to massive BHs of ~ 10^5 M_sun, as long as the rapid accretion is maintained.
Protoplanetary disks are the birthplaces of planetary systems. The evolution of the star-disk system and the disk chemical composition determines the initial conditions for planet formation. Therefore a comprehensive understanding of the main physical and chemical processes in disks is crucial for our understanding of planet formation. We give an overview of the early evolution of disks, discuss the importance of the stellar high-energy radiation for disk evolution and describe the general thermal and chemical structure of disks. Finally we provide an overview of observational tracers of the gas component and disk winds.
We present the science cases and technological discussions that came from the workshop entitled "Finding the UV-Visible Path Forward" held at NASA GSFC June 25-26, 2015. The material presented outlines the compelling science that can be enabled by a next generation space-based observatory dedicated for UV-visible science, the technologies that are available to include in that observatory design, and the range of possible alternative launch approaches that could also enable some of the science. The recommendations to the Cosmic Origins Program Analysis Group from the workshop attendees on possible future development directions are outlined.
In this work, we report the discovery of a candidate planetary-mass object with a photoevaporating protoplanetary disk, Proplyd 133-353, which is near the massive star $\theta^{1}$ Ori C at the center of the Orion Nebula Cluster (ONC). The object was known to have extended emission pointing away from $\theta^{1}$ Ori C, indicating ongoing external photoevaporation. Our near-infrared spectroscopic data suggests that the central source of Proplyd 133-353 is substellar ($\sim$M9.5), might have a mass probably less than 13 Jupiter mass and an age younger than 0.5 Myr. Proplyd 133-353 shows a similar ratio of X-ray luminosity to stellar luminosity to other young stars in the ONC with a similar stellar luminosity, and has a similar proper motion to the mean one of confirmed ONC members. We propose that Proplyd 133-353 was formed in a very low-mass dusty cloud near $\theta^{1}$ Ori C as a second-generation of star formation, which can explain both its young age and the presence of its disk.
This review presents a comprehensive overview of galaxy bias, that is, the statistical relation between the distribution of galaxies and matter. We focus on large scales where cosmic density fields are quasi-linear. On these scales, the clustering of galaxies can be described by a perturbative bias expansion, and the complicated physics of galaxy formation is absorbed by a finite set of coefficients of the expansion, called bias parameters. The review begins with a pedagogical proof of this very important result, which forms the basis of the rigorous perturbative description of galaxy clustering, under the assumptions of General Relativity and Gaussian, adiabatic initial conditions. Key components of the bias expansion are all leading local gravitational observables, which includes the matter density but also tidal fields and their time derivatives. We hence expand the definition of local bias to encompass all these contributions. This derivation is followed by a presentation of the peak-background split in its general form, which elucidates the physical meaning of the bias parameters, and a detailed description of the connection between bias parameters and galaxy (or halo) statistics. We then review the excursion set formalism and peak theory which provide predictions for the values of the bias parameters. In the remainder of the review, we consider the generalizations of galaxy bias required in the presence of various types of cosmological physics that go beyond pressureless matter with adiabatic, Gaussian initial conditions: primordial non-Gaussianity, massive neutrinos, baryon-CDM isocurvature perturbations, dark energy, and modified gravity. Finally, we discuss how the description of galaxy bias in the galaxies' rest frame is related to observed clustering statistics measured from the observed angular positions and redshifts in actual galaxy catalogs.
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We present the exact solutions for the collapse of a spherically-symmetric, cold (i.e., pressureless) cloud under its own self-gravity, valid for arbitrary initial density profiles and not restricted to the realm of self-similarity. These solutions exhibit a number of remarkable features, including the self-consistent formation of and subsequent accretion onto a central point mass. A number of specific examples are provided, and we show that Penston's solution of pressureless, self-similar collapse is recovered for polytropic density profiles; importantly, however, we demonstrate that the time over which this solution holds is fleetingly narrow, implying that much of the collapse proceeds non-self-similarly. We show that our solutions can naturally incorporate turbulent pressure support, and we investigate the evolution of overdensities -- potentially generated by such turbulence -- as the collapse proceeds. Finally, we analyze the evolution of the angular velocity and magnetic fields in the limit that their dynamical influence is small, and we recover exact solutions for these quantities. Our results may provide important constraints on numerical models that attempt to elucidate the details of protostellar collapse when the initial conditions are far less idealized.
We present results from a deep 2'x3' (comoving scale of 3.7 Mpc x 5.5 Mpc at z=3) survey at 1.1 mm taken with the Atacama Large Millimeter/submillimeter Array (ALMA) in the SSA22 field. We observe the core region of a z = 3.09 protocluster, achieving a typical rms sensitivity of 60 micro-Jy/beam at a spatial resolution of 0".7. We detect 18 robust ALMA sources at a signal-to-noise ratio (SNR) > 5. Comparison between the ALMA map and a 1.1 mm map taken with the AzTEC camera on the Atacama Submillimeter Telescope Experiment (ASTE) indicates that three submillimeter sources discovered by the AzTEC/ASTE survey are resolved into eight individual submillimeter galaxies (SMGs) by ALMA. At least ten of our 18 ALMA SMGs have spectroscopic redshifts of z = 3.09, placing them in the protocluster. This shows that a number of dusty starburst galaxies are forming simultaneously in the core of the protocluster. The nine brightest ALMA SMGs with SNR > 10 have a median intrinsic angular size of 0".32+0".13-0".06 (2.4+1.0-0.4 physical kpc at z = 3.09), which is consistent with previous size measurements of SMGs in other fields. As expected the source counts show a possible excess compared to the counts in the general fields at S_1.1mm >= 1.0 mJy due to the protocluster. Our contiguous mm mapping highlights the importance of large-scale structures on the formation of dusty starburst galaxies.
We systematically investigate the near- (NIR) to far-infrared (FIR) photometric properties of a nearly complete sample of local active galactic nuclei (AGN) detected in the Swift/Burst Alert Telescope (BAT) all-sky ultra hard X-ray (14-195 keV) survey. Out of 606 non-blazar AGN in the Swift/BAT 70-month catalog at high galactic latitude of $|b|>10^{\circ}$, we obtain IR photometric data of 604 objects by cross-matching the AGN positions with catalogs from the WISE, AKARI, IRAS, and Herschel infrared observatories. We find a good correlation between the ultra-hard X-ray and mid-IR (MIR) luminosities over five orders of magnitude ($41 < \log (L_{14-195}/{\rm erg}~{\rm s}^{-1})< 46$). Informed by previous measures of the intrinsic spectral energy distribution of AGN, we find FIR pure-AGN candidates whose FIR emission is thought to be AGN-dominated with low starformation activity. We demonstrate that the dust covering factor decreases with the bolometric AGN luminosity, confirming the luminosity-dependent unified scheme. We also show that the completeness of the WISE color-color cut in selecting Swift/BAT AGN increases strongly with 14-195 keV luminosity.
There is good evidence that the centers of massive early-type galaxies have a bottom-heavy stellar initial mass function (IMF) compared to the IMF of the Milky Way. Here we study the radial variation of the IMF within such galaxies, using a combination of high quality Keck spectroscopy and a new suite of stellar population synthesis models that cover a wide range in [Z/H]. As in the previous studies in this series, the models are fit directly to the spectra and treat all elemental abundance ratios as free parameters. Using newly obtained spectroscopy for six galaxies, including deep data extending to ~1Re for the galaxies NGC1407, NGC1600, and NGC2695, we find that the IMF strongly varies with galactocentric radius. For all galaxies the IMF is bottom-heavy in the central regions, with average "mismatch" parameter a~2.5 at r=0. The IMF rapidly becomes more bottom-light with increasing radius, flattening off near the Milky Way value (a~1.1) at R>0.4Re. A consequence is that the luminosity-weighted average IMF depends on the measurement aperture: within R=Re we find <a>=1.3-1.5, that is, the IMF of even the most massive galaxies is only mildly bottom-heavy within the half-light radius. Our results are consistent with several earlier studies that were based on analyses of radial gradients of line indices, and support galaxy formation models in which the central regions of massive galaxies had a different formation history than their outer parts. Finally, we make use of the high signal-to-noise central spectra of NGC1407 and NGC2695 to demonstrate that we are indeed measuring IMF effects, not abundance effects.
The Ly$\alpha$ escape fraction is a key measure to constraining the neutral state of the inter-galactic medium and then to understanding how the universe was fully reionized. We combine deep narrow-band imaging data through the custom-made filter NB393 and the $H_{2}S$1 filter centered at 2.14 $\mu$m to examine the Ly$\alpha$ emitters and H$\alpha$ emitters at the same redshift $z=2.24$. The combination of two populations allows us to determine the Ly$\alpha$ escape fraction at $z=2.24$. Over an area of 383 arcmin$^{2}$ in the Extended Chandra Deep Field (ECDFS), 124 Ly$\alpha$ emitters are detected down to NB393 = 26.4 mag at the 5$\sigma$ level and 56 H$\alpha$ emitters from An14. Of them, four have both Ly$\alpha$ and H$\alpha$ emissions (LAHAEs). We measure the individual/volumetric Ly$\alpha$ escape fraction by comparing the observed Ly$\alpha$ luminosity/luminosity density to extinction-corrected H$\alpha$ luminosity/luminosity density. We revisit the extinction correction for H$\alpha$ emitters using the Galactic extinction law with the color excess for nebular emission. We also adopt the Calzetti extinction law together with an identical color excess for stellar and nebular regions to explore how the uncertainties in extinction correction affect our results. In both cases, an anti-correlation between the Ly$\alpha$ escape fraction and dust attenuation is found among the LAHAEs, suggesting that dust absorption is responsible for the suppression of the escaping Ly$\alpha$ photons. However, the estimated Ly$\alpha$ escape fraction of individual LAHAEs varies up to ~3 percentage points between the two methods of extinction correction. We find the global Ly$\alpha$ escape fraction at $z=2.24$ to be ($3.7\pm1.4$)% in ECDFS. The variation in color excess of extinction causes a discrepancy of ~1 percentage point in global Ly$\alpha$ escape fraction.
We present an analysis of the mass distribution in the region of the Galactic bulge, which leads to constraints on the total amount and distribution of Dark Matter (DM) therein. Our results -based on the dynamical measurement of the BRAVA collaboration- are quantitatively compatible with those of a recent analysis, and generalised to a vaste sample of observationally inferred morphologies of the stellar components in the region of the Galactic bulge. By fitting the inferred DM mass to a generalised NFW profile, we find that cores (index gamma smaller than 0.6) are forbidden only for very light configurations of the bulge, and that cusps (index gamma bigger than 1.2) are allowed, but not necessarily preferred. Interestingly, we find that the results for the bulge region are compatible with those obtained with dynamical methods (based on the rotation curve) applied to outer regions of the Milky Way, for all morphologies adopted. We find that the uncertainty on the shape of the stellar morphology heavily affects the determination of the DM distribution in the bulge region, which is gravitationally dominated by baryons, adding up to the uncertainty on its normalization. The combination of the two hinders the actual possibility to infer sound conclusions about the distribution of DM in the region of the Galactic bulge, and only future observations of the stellar census and dynamics in this region will bring us closer to a quantitatively more definite answer.
We explore the use of mm-wave emission line ratios to trace molecular gas density when observations integrate over a wide range of volume densities within a single telescope beam. For observations targeting external galaxies, this case is unavoidable. Using a framework similar to that of Krumholz and Thompson (2007), we model emission for a set of common extragalactic lines from lognormal and power law density distributions. We consider the median density of gas producing emission and the ability to predict density variations from observed line ratios. We emphasize line ratio variations, because these do not require knowing the absolute abundance of our tracers. Patterns of line ratio variations have the prospect to illuminate the high-end shape of the density distribution, and to capture changes in the dense gas fraction and median volume density. Our results with and without a high density power law tail differ appreciably; we highlight better knowledge of the PDF shape as an important area. We also show the implications of sub-beam density distributions for isotopologue studies targeting dense gas tracers. Differential excitation often implies a significant correction to the naive case. We provide tabulated versions of many of our results, which can be used to interpret changes in mm-wave line ratios in terms of changes in the underlying density distributions.
In the Milky Way there are thousands of stellar clusters each harboring from a hundred to a million stars. Although clusters are common, the initial conditions of cluster formation are still not well understood. To determine the processes involved in the formation and evolution of clusters it is key to determine the global properties of cluster-forming clumps in their earliest stages of evolution. Here, we present the physical properties of 1,244 clumps identified from the MALT90 survey. Using the dust temperature of the clumps as a proxy for evolution we determined how the clump properties change at different evolutionary stages. We find that less-evolved clumps exhibiting dust temperatures lower than 20 K have higher densities and are more gravitationally bound than more-evolved clumps with higher dust temperatures. We also identified a sample of clumps in a very early stage of evolution, thus potential candidates for high-mass star-forming clumps. Only one clump in our sample has physical properties consistent with a young massive cluster progenitor, reinforcing the fact that massive proto-clusters are very rare in the Galaxy.
This paper presents a study of the chemical compositions in cool gas around a sample of 27 intermediate-redshift galaxies. The sample comprises 13 massive quiescent galaxies at z=0.40-0.73 probed by QSO sightlines at projected distances d=3-400 kpc, and 14 star-forming galaxies at z=0.10-1.24 probed by QSO sightlines at d=8-163 kpc. The main goal of this study is to examine the radial profiles of the gas-phase Fe/{\alpha} ratio in galaxy halos based on the observed Fe II to Mg II column density ratios. Because Mg+ and Fe+ share similar ionization potentials, the relative ionization correction is small in moderately ionized gas and the observed ionic abundance ratio N(Fe II)/N(Mg II) places a lower limit to the underlying (Fe/Mg) elemental abundance ratio. For quiescent galaxies, a median and dispersion of log <N(Fe II)/N(Mg II)> =-0.06+/-0.15 is found at d<~60 kpc, which declines to log <N(Fe II)/N(Mg II)> <-0.3 at d>~100 kpc. On the other hand, star-forming galaxies exhibit log <N(Fe II)/N(Mg II)> =-0.25+/-0.21 at d<~60 kpc and log <N(Fe II)/N(Mg II)> =-0.9+/-0.4 at larger distances. Including possible differential dust depletion or ionization correction would only increase the inferred (Fe/Mg) ratio. The observed N(FeII)/N(Mg II) implies super-solar Fe/{\alpha} ratios in the inner halo of quiescent galaxies. An enhanced Fe abundance indicates a substantial contribution by Type Ia supernovae in the chemical enrichment, which is at least comparable to what is observed in the solar neighborhood or in intracluster media but differs from young star-forming regions. In the outer halos of quiescent galaxies and in halos around star-forming galaxies, however, the observed N(Fe II)/N(Mg II) is consistent with an {\alpha}-element enhanced enrichment pattern, suggesting a core-collapse supernovae dominated enrichment history.
We report the detection of accreting ionized gas at the disk-halo interface of the nearby galaxy M33. We analyze HST/COS absorption-line spectra of seven ultraviolet-bright stars evenly distributed across the disk of M33. We find Si IV absorption components consistently redshifted relative to the bulk M33's ISM absorption along all the sightlines. The Si IV detection indicates an enriched, disk-wide, ionized gas inflow toward the disk. This inflow is most likely multi-phase as the redshifted components can also be observed in ions with lower ionization states (e.g., S II, P II, Fe II, Si II). Kinematic modeling of the inflow is consistent with an accreting layer at the disk-halo interface of M33, which has an accretion velocity of 110$^{+15}_{-20}$ km s$^{-1}$ at a distance of 1.5$^{+1.0}_{-1.0}$ kiloparsec above the disk. The modeling indicates a total mass of $\sim3.9\times10^7$ M$_{\odot}$ for the accreting material at the disk-halo interface on the near side of the M33 disk , with an accretion rate of $\sim2.9$ M$_{\odot}$ yr$^{-1}$. The high accretion rate and the level of metal-enrichment suggest the inflow is likely to be the fall back of M33 gas from a galactic fountain and/or the gas pulled loosed during a close interaction between M31 and M33. Our study of M33 is the first to unambiguously reveal the existence of a disk-wide, ionized gas inflow beyond the Milky Way, providing a better understanding of gas accretion in the vicinity of a galaxy disk.
We perform a theoretical analysis of the observational relation between angular momentum and mass (richness) of the galaxy clusters. For that we calculate the distribution function of astronomical objects (like galaxies and/or smooth halos of different kinds) gravitational fields due to their tidal interaction. Within the statistical method of Chandrasekhar we are able to show that the distribution function is determined by the form of interaction between objects and for multipole (tidal) interaction it is never Gaussian. Our calculation permits to demonstrate that alignment of galaxies angular momenta increases with the cluster richness. The specific form of the corresponding dependence is due to assumptions made about cluster morphology.
Using a suite of three large cosmological hydrodynamical simulations, Horizon-AGN, Horizon-noAGN (no AGN feedback) and Horizon-DM (no baryons), we investigate how a typical sub-grid model for AGN feedback affects the evolution of the inner density profiles of massive dark matter haloes and galaxies. Based on direct object-to-object comparisons, we find that the integrated inner mass and density slope differences between objects formed in these three simulations (hereafter, H_AGN, H_noAGN and H_DM) significantly evolve with time. More specifically, at high redshift (z~5), the mean central density profiles of H_AGN and H_noAGN dark matter haloes tend to be much steeper than their H_DM counterparts owing to the rapidly growing baryonic component and ensuing adiabatic contraction. By z~1.5, these mean halo density profiles in H_AGN have flattened, pummelled by powerful AGN activity ("quasar mode"): the integrated inner mass difference gaps with H_noAGN haloes have widened, and those with H_DM haloes have narrowed. Fast forward 9.5 billion years, down to z=0, and the trend reverses: H_AGN halo mean density profiles drift back to a more cusped shape as AGN feedback efficiency dwindles ("radio mode"), and the gaps in integrated central mass difference with H_noAGN and H_DM close and broaden respectively. On the galaxy side, the story differs noticeably. Averaged stellar profile central densities and inner slopes are monotonically reduced by AGN activity as a function of cosmic time, resulting in better agreement with local observations. As both dark matter and stellar inner density profiles respond quite sensitively to the presence of a central AGN, there is hope that future observational determinations of these quantities can be used constrain AGN feedback models.
We present subarcsecond images of submillimeter CO and continuum emission from a local galaxy forming massive star clusters: the blue compact dwarf galaxy II Zw 40. At $\sim$0.4" resolution (20 pc), the CO(3-2), CO(1-0), 3mm and 870${\mu}$m continuum maps illustrate star formation on the scales of individual molecular clouds. Dust contributes about a third of the 870${\mu}$m continuum emission, with free-free accounting for the rest. On these scales, there is not a good correspondence between gas, dust, and free-free emission. Dust continuum is enhanced toward the star-forming region as compared to the CO emission. We suggest that an unexpectedly low and spatially variable gas-to-dust ratio is the result of massive clusters of the starburst.
The gas in galaxies is both the fuel for star formation and a medium that attenuates the light of the young stars. We study the relations between UV attenuation, spectral slope, star formation rates, and molecular gas surface densities in a sample of 28 z$\sim$1 and a reference sample of 32 z$\sim$0 galaxies that are detected in CO, far-infrared, and rest frame UV. The samples are dominated by disc-like galaxies close to the main SFR--mass relation. We find that the location of the z$\sim$1 galaxies on the IRX-$\beta$ plane is correlated with their gas-depletion time-scale $\tau_{dep}$ and can predict $\tau_{dep}$ with a standard deviation of 0.16 dex. We use IRX-$\beta$ to estimate the mean total gas column densities at the locations of star formation in the galaxies, and compare them to the mean molecular gas surface densities as measured from CO. We confirm previous results regarding high $N_H/A_V$ in z$\sim$1 galaxies. We estimate an increase in the gas filling factor by a factor of 4--6 from z$\sim$0 to z$\sim$1 and a corresponding increase of factor 3--2 in the mean column densities of the star forming clouds. After accounting for the filling factor, the z$\sim$1 and the z$\sim$0 samples exhibit similar attenuation properties. These indicate to similar porous geometries to the molecular clouds in star-forming disc galaxies at 0<z<1.
We describe a sub-galactic main sequence (SGMS) relating star formation rate surface density ($\Sigma_{\textrm{SFR}}$) and stellar mass density ($\Sigma_{\star}$) for distinct regions within star forming galaxies, including their nuclei. We use a sample of 246 nearby star-forming galaxies from the "Star Formation Reference Survey" and demonstrate that the SGMS holds down to $ \sim $1 kpc scales with a slope of $\alpha=0.91$ and a dispersion of 0.31 dex, similar to the well-known main sequence (MS) measured for globally integrated star formation rates (SFRs) and stellar masses. The SGMS slope depends on galaxy morphology, with late-type galaxies (Sc$-$Irr) having $\alpha = 0.97$ and early-type spirals (Sa$-$Sbc) having $\alpha = 0.81$. The SGMS constructed from sub-regions of individual galaxies has on average the same characteristics as the composite SGMS from all galaxies. The SGMS for galaxy nuclei shows a dispersion similar to that seen for other sub-regions. Sampling a limited range of SFR$-$M$_{\star} $ space may produce either sub-linearity or super-linearity of the SGMS slope. For nearly all galaxies, both SFR and stellar mass peak in the nucleus, indicating that circumnuclear clusters are among the most actively star-forming regions in the galaxy and the most massive. The nuclear SFR also correlates with total galaxy mass, forming a distinct sequence from the standard MS of star-formation. The nuclear main sequence will be useful for studying bulge growth and for characterizing feedback processes connecting AGN and star formation.
Many young star clusters appear to be fractal, i.e. they appear to be concentrated in a nested hierarchy of clusters within clusters. We present a new algorithm for statistically analysing the distribution of stars to quantify the level of sub-structure. We suggest that, even at the simplest level, the internal structure of a fractal cluster requires the specification of three parameters. (i) The 3D fractal dimension, $\mathcal{D}$, measures the extent to which the clusters on one level of the nested hierarchy fill the volume of their parent cluster. (ii) The number of levels, $\mathcal{L}$, reflects the finite ratio between the linear size of the large root-cluster at the top of the hierarchy, and the smallest leaf-clusters at the bottom of the hierarchy. (iii) The volume-density scaling exponent, $\mathcal{C}=-\textrm{d}\ln[\delta n]/\textrm{d}\ln[L]$ measures the factor by which the excess density, $\delta n$, in a structure of scale $L$, exceeds that of the background formed by larger structures; it is similar, but not exactly equivalent, to the exponent in Larson's scaling relation between density and size for molecular clouds. We describe an algorithm which can be used to constrain the values of $({\cal D},{\cal L},{\cal C})$ and apply this method to artificial and observed clusters. We show that this algorithm is able to reliably describe the three dimensional structure of an artificial star cluster from the two dimensional projection, and quantify the varied structures observed in real and simulated clusters.
The kinematic and dynamical properties of galaxy stellar halos are difficult to measure because of the faint surface brightness that characterizes these regions. Spiral galaxies can be probed using the radio HI emission; on the contrary, early-type galaxies contain less gas, therefore alternative kinematic tracers need to be used. Planetary nebulae (PNe) can be easily detected far out in the halo thanks to their bright emission lines. It is therefore possible to map the halo kinematics also in early-type galaxies, typically out to 5 effective radii or beyond. Thanks to the recent spectroscopic surveys targeting extra-galactic PNe, we can now rely on a few tens of galaxies where the kinematics of the stellar halos are measured. Here, I will review the main results obtained in this field in the last decades.
We examine the constraints imposed by Faraday rotation measures of extragalactic point sources on the structure of the magnetic field in the halo of our Galaxy. Guided by radio polarization observations of external spiral galaxies, we look in particular into the possibility that field lines in the Galactic halo have an X shape. We employ the analytical models of spiraling, possibly X-shape magnetic fields derived in a previous paper to generate synthetic all-sky maps of the Galactic Faraday depth, which we fit to an observational reference map with the help of Markov Chain Monte Carlo simulations. We find that the magnetic field in the Galactic halo is slightly more likely to be bisymmetric (azimuthal wavenumber, $m = 1$) than axisymmetric ($m = 0$). If it is indeed bisymmetric, it must appear as X-shaped in radio polarization maps of our Galaxy seen edge-on from outside, but if it is actually axisymmetric, it must instead appear as nearly parallel to the Galactic plane.
Nearly 50 years ago, in the proceedings of the first IAU symposium on planetary nebulae, Lawrence H. Aller and Stanley J. Czyzak said that "the problem of determination of the chemical compositions of planetary and other gaseous nebulae constitutes one of the most exasperating problems in astrophysics". Although the situation has greatly improved over the years, many important problems are still open and new questions have arrived to the field, which still is an active field of study. Here I will review some of the main aspects related to the determination of gaseous abundances in PNe and some relevant results derived in the last five year, since the last IAU symposium on PNe.
We report on the redshift of the BL Lac object 3FGL J0909.0+2310 based on observations obtained with the OSIRIS Multi Object Spectrograph (MOS) mounted on the 10.4-m Gran Telescopio Canarias. A redshift of 0.432+/-0.002 was obtained by the identification of three absorption features (CaII K&H and G-band) detected in the spectrum of the BL Lac host galaxy. The closest object to the BL Lac at an angular separation of 3.8" (~21 kpc at this distance) has a similar redshift of 0.431+/-0.002. This companion galaxy could be the most likely cause of the nuclear activity as postulated by studies based on more extended data sets and cosmological models. MOS allows us to study the object's neighbourhood within a field of view of approximately 7'x2' and we find two small groups of galaxies at redshifts 0.28 and 0.39 which are probably not related to the activity of 3FGL~J0909.0+2310.
We investigate the physical conditions of the gas, atomic and molecular, in the filaments in the context of Photo-Dissociation Regions (PDRs) using the KOSMA-PDR mode of clumpy clouds. We also compare the [CII] vs. [NII] integrated intensity predictions in Abel et al. 2005 for HII regions and adjacent PDRs in the Galactic disk, and check for their applicability under the extreme physical conditions present in the GC. Our preliminary results show that observed integrated intensities are well reproduced by the PDR model. The gas is exposed to a relatively low Far-UV field between 10^2 - 10^3 Draine fields. The total volume hydrogen density is well constrained between 10^4 - 10^5 cm^-3. The hydrogen ionization rate due to cosmic-rays varies between 10^-15 and 4x10^-15 s^-1, with the highest value ~ 10^-14 s^-1 found towards G0.07+0.04. Our results show that the line-of-sight contribution to the total distance of the filaments to the Arches Cluster is not negligible. The spatial distribution of the [CII]/[NII] ratio shows that the integrated intensity ratios are fairly homogeneously distributed for values below 10 in energy units. Calculations including variation on the [C/N] abundance ratio show that tight constraints on this ratio are needed to reproduce the observations.
The number, distribution, and properties of dwarf satellites are crucial probes of the physics of galaxy formation at low masses and the response of satellite galaxies to the tidal and gas dynamical effects of their more massive parent.To make progress, it is necessary to augment and solidify the census of dwarf satellites of galaxies outside the Local Group. M\"uller et al. (2015) presented 16 dwarf galaxy candidates near M83, but lacking reliable distances, it is unclear which candidates are M83 satellites. Using red giant branch stars from the HST/GHOSTS survey in conjunction with ground-based images from VLT/VIMOS, we confirm that one of the candidates, dw1335-29-- with a projected distance of 26 kpc from M83 and a distance modulus of $(m - M)_0 = 28.5^{+0.3}_{-0.1}$ -- is a satellite of M83. We estimate an absolute magnitude $M_V = -10.1 \pm{0.4}$, an ellipticity of $0.40^{+0.14}_{-0.22}$, a half light radius of $656^{+121}_{-170 }$ pc, and [Fe/H] = $-1.3^{+0.3}_{-0.4}$. Owing to dw1335-29's somewhat irregular shape and possible young stars, we classify this galaxy as a dwarf irregular or transition dwarf. This is curious, as with a projected distance of 26 kpc from M83, dw1335-29 is expected to lack recent star formation. Further study of M83's dwarf population will reveal if star formation in its satellites is commonplace (suggesting a lack of a hot gas envelope for M83 that would quench star formation) or rare (suggesting that dw1335-29 has a larger M83-centric distance, and is fortuitously projected to small radii).
We develop two algorithms, based on maximum likelihood (ML) inference, for estimating the parameters of polarized radio sources which emit at a single rotation measure (RM), e.g., pulsars. These algorithms incorporate the flux density spectrum of the source, either a power law or a scaled version of the Stokes I spectrum, and a variation in sensitivity across the observing band. We quantify the detection significance and measurement uncertainties in the fitted parameters, and we derive weighted versions of the RM synthesis algorithm which, under certain conditions, maximize the likelihood. We use Monte Carlo simulations to compare injected and recovered source parameters for a range of signal-to-noise ratios, investigate the quality of standard methods for estimating measurement uncertainties, and search for statistical biases. These simulations consider one frequency band each for the Australia Telescope Compact Array (ATCA), the Square Kilometre Array (SKA), and the Low Frequency Array (LOFAR). We find that results obtained for one frequency band cannot be easily generalized, and that methods which were developed in the past for correcting bias in individual frequency channels do not apply to wide-band data sets. The standard method for estimating the measurement uncertainty in RM is not accurate for sources with non-zero spectral indices. Furthermore, dividing Stokes Q and U by Stokes I to correct for spectral index effects, in combination with RM synthesis, does not maximize the likelihood.
We reexamine the dynamical evolution of the mass and luminosity functions of globular star clusters (GCMF and GCLF). Fall & Zhang (2001, hereafter FZ01) showed that a power-law MF, as commonly seen among young cluster systems, would evolve by dynamical processes over a Hubble time into a peaked MF with a shape very similar to the observed GCMF in the Milky Way and other galaxies. To simplify the calculations, the semi-analytical FZ01 model adopted the "classical" theory of stellar escape from clusters, and neglected variations in the $M/L$ ratios of clusters. Kruijssen & Portegies Zwart (2009, hereafter KPZ09) modified the FZ01 model to include "retarded" and mass-dependent stellar escape, the latter causing significant $M/L$ variations. KPZ09 asserted that their model was compatible with observations whereas the FZ01 model was not. We show here that this claim is not correct; the FZ01 and KPZ09 models fit the observed Galactic GCLF equally well. We also show that there is no detectable correlation between $M/L$ and $L$ for GCs in the Milky Way and Andromeda galaxies, in contradiction with the KPZ09 model. Our comparisons of the FZ01 and KPZ09 models with observations can be explained most simply if stars escape at rates approaching the classical limit for high-mass clusters, as expected on theoretical grounds.
We present and analyse an extensive dataset of the superluminous supernova LSQ14mo (z = 0.256), consisting of a multi-colour lightcurve from -30 d to +70 d in the rest-frame and a series of 6 spectra from PESSTO covering -7 d to +50 d. This is among the densest spectroscopic coverage, and best-constrained rising lightcurve, for a fast-declining hydrogen-poor superluminous supernova. The bolometric lightcurve can be reproduced with a millisecond magnetar model with ~ 4 M_sol ejecta mass, and the temperature and velocity evolution is also suggestive of a magnetar as the power source. Spectral modelling indicates that the SN ejected ~ 6 M_sol of CO-rich material with a kinetic energy of ~ 7 x 10^51 erg, and suggests a partially thermalised additional source of luminosity between -2 d and +22 d. This may be due to interaction with a shell of material originating from pre-explosion mass loss. We further present a detailed analysis of the host galaxy system of LSQ14mo. PESSTO and GROND imaging show three spatially resolved bright regions, and we used the VLT and FORS2 to obtain a deep (5-hour exposure) spectra of the SN position and the three star-forming regions, which are at a similar redshift. The FORS spectrum at +300 days shows no trace of supernova emission lines and we place limits on the strength of [O I] from comparisons with other Ic supernovae. The deep spectra provides a unique chance to investigate spatial variations in the host star-formation activity and metallicity. The specific star-formation rate is similar in all three components, as is the presence of a young stellar population. However, the position of LSQ14mo exhibits a lower metallicity, with 12 + log(O/H) = 8.2 in both the R23 and N2 scales (corresponding to ~ 0.3 Z_sol). We propose that the three bright regions in the host system are interacting, which thus triggers star-formation and forms young stellar populations.
Protoplanetary disks form around stars as a consequence of pre-stellar cores collapsing in filaments of Giant Molecular Clouds, which makes them the smallest entity in a hierarchy of scales. Length scales range from tens of parsecs for Giant Molecular Clouds to protoplanetary disk sizes $\sim 10$ AU to $\sim 100$ AU. It is computationally very challenging to cover such a broad range of scales in a single simulation. Therefore, simulations of protostellar formation traditionally start from initial conditions representing a collapsing spherically symmetric cloud, as an approximation for the pre-stellar core. This approach allows detailed parameter studies, but neglecting the underlying turbulence in Giant Molecular Clouds and the potential interactions with the surroundings could potentially limit the applicability of such idealized initial conditions. Considering the Giant Molecular Cloud dynamics is important to investigate the protostellar formation process in a statistically unbiased sample of initial conditions. Fortunately, relevant spatial as well as temporal scales for large scale dynamics are larger than for smaller domains due to Larson's velocity law. Using extreme adaptive mesh refinement we carry out simulations with a maximal resolution of 2 AU around single protostars properly anchored in a 40 pc model of GMC using a modified version of the \ramses\ code to solve the equations of ideal magnetohydrodynamics including microphysics and a sub-grid sink particle representation of protostars. In this study, we present for the first time the formation process around nine different solar mass stars embedded in their large-scale environment determined by Giant Molecular Cloud dynamics. We find that protostellar accretion including the formation of protoplanetary disks is a heterogeneous process due to the different protostellar environments.
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We present new ALMA band-7 data for a sample of six luminous quasars at z~4.8, powered by fast-growing supermassive black holes (SMBHs) with rather uniform properties: the typical accretion rates and black hole masses are L/L_Edd~0.7 and M_BH~10^9 M_sol. Our sample consists of three "FIR-bright" sources which were individually detected in previous Herschel/SPIRE observations, with star formation rates of SFR>1000 M_sol/yr, and three "FIR-faint" sources for which Herschel stacking analysis implies a typical SFR of ~400 M_sol/yr. The dusty interstellar medium in the hosts of all six quasars is clearly detected in the ALMA data, and resolved on scales of 2 kpc, in both continuum (\lambda_rest~150um) and [CII]157.74um line emission. The continuum emission is in good agreement with the expectations from the Herschel data, confirming the intense SF activity in the quasars' hosts. Importantly, we detect companion sub-mm galaxies (SMGs) for three sources -- one FIR-bright and two FIR-faint, separated by ~14-45 kpc and <450 km/s from the quasar hosts. The [CII]-based dynamical mass estimates for the interacting SMGs are within a factor of ~3 of the quasar hosts' masses, while the continuum emission implies SFR(quasar)~(2-11)xSFR(SMG). Our ALMA data therefore clearly support the idea that major mergers may be important drivers for rapid, early SMBH growth. However, the fact that not all high-SFR quasar hosts are accompanied by interacting SMGs, and the gas kinematics as observed by ALMA, suggest that other processes may fueling these systems. Our analysis thus demonstrates the diversity of host galaxy properties and gas accretion mechanisms associated with early and rapid SMBH growth.
It is now well-established that the stellar initial mass function (IMF) can be determined from the absorption line spectra of old stellar systems, and this has been used to measure the IMF and its variation across the early-type galaxy population. Previous work focused on measuring the slope of the IMF over one or more stellar mass intervals, implicitly assuming that this is a good description of the IMF and that the IMF has a universal low-mass cutoff. In this work we consider more flexible IMFs, including two-component power-laws with a variable low-mass cutoff and a general non-parametric model. We demonstrate with mock spectra that the detailed shape of the IMF can be accurately recovered as long as the data quality are high (S/N$\gtrsim300$) and cover a wide wavelength range (0.4um-1.0um). We apply these flexible IMF models to a high S/N spectrum of the center of the massive elliptical galaxy NGC 1407. Fitting the spectrum with non-parametric IMFs, we find that the IMF in the center shows a continuous rise extending toward the hydrogen-burning limit, with a behavior that is well-approximated by a power-law with an index of -2.7. These results provide strong evidence for the existence of extreme (super-Salpeter) IMFs in the cores of massive galaxies.
We study dusty winds driven by radiation pressure in the atmosphere of a rapidly star-forming environment. We apply the variable Eddington tensor algorithm to re-examine the two-dimensional radiation hydrodynamic problem of a column of gas that is accelerated by a constant infrared radiation flux. In the absence of gravity, the system can be characterized by the initial optical depth of the gas. We perform several runs with different initial optical depth and resolution. We find that the gas spreads out along the vertical direction, as its mean velocity and velocity dispersion increase. In contrast to previous work using flux-limited diffusion algorithm, we find little evolution in the trapping factor. The momentum coupling between radiation and gas in the absence of gravity is similar to that with gravity. For Eddington ratio increasing with the height in the system, the momentum transfer from the radiation to the gas is not merely $\sim L/c$, but amplified by a factor of $1+\eta \tau_{\rm IR}$, where $\tau_{\rm IR}$ is the integrated infrared optical depth through the system, and $\eta\sim0.5-0.9$, decreasing with the optical depth. We apply our results to the atmosphere of galaxies and conclude that radiation pressure may be an important mechanism for driving winds in rapidly star-forming galaxies and starbursts.
We constrain the possible presence of a central black hole (BH) in the center of the Large Magellanic Cloud (LMC). This requires spectroscopic measurements over an area of order a square degree, due to the poorly known position of the kinematic center. Such measurements are now possible with the impressive field of view of the Multi Unit Spectroscopic Explorer (MUSE) on the ESO Very Large Telescope. We used the Calcium Triplet (~850nm) spectral lines in many short-exposure MUSE pointings to create a two-dimensional integrated-light line-of-sight velocity map from the ~$10^8$ individual spectra, taking care to identify and remove Galactic foreground populations. The data reveal a clear velocity gradient at an unprecedented spatial resolution of 1 arcmin$^{2}$. We fit kinematic models to arrive at a $3\sigma$ upper-mass-limit of $9\times10^{6}$ M$_{Sun}$ for any central BH - consistent with the known scaling relations for supermassive black holes and their host systems. This adds to the growing body of knowledge on the presence of BHs in low-mass and dwarf galaxies, and their scaling relations with host-galaxy properties, which can shed light on theories of BH growth and host system interaction.
We explore via spectroscopic modeling whether the highly correlated diffuse interstellar bands at 6613.6 and 6196.0 {\AA} might originate from a single molecule. Efforts were made to simulate the band contours of the DIBs along the three lines-of-sight, which have been observed by others at high resolution: HD179406, HD174165, and Her 36. Reasonable simultaneous fits were obtained using a prolate symmetric top molecule that exhibits transitions of two different band types, type-a parallel and type-b perpendicular bands. Two different excited states of a long- or heavy-chain, forked molecule are proposed. A minimum number of adjustable parameters were used including ground and excited state A and B rotational constants, an excited state centrifugal distortion constant, and three different rotational excitation temperatures. Points in favor and against the hypothesis are discussed.
We present new observations of the three nearest early-type galaxy (ETG) strong lenses discovered in the SINFONI Nearby Elliptical Lens Locator Survey (SNELLS). Based on their lensing masses, they were inferred to have a stellar initial mass function (IMF) consistent with that of the Milky Way, not the bottom-heavy IMF that has been reported as typical for high-$\sigma$ ETGs based on lensing, dynamical, and stellar population synthesis techniques. We use these unique systems to test the consistency of IMF estimates derived from different methods. We first estimate the stellar $M_*/L$ using lensing and stellar dynamics. We then fit high-quality optical spectra of the lenses using an updated version of the stellar population synthesis models developed by Conroy & van Dokkum. When examined individually, we find find good agreement among these methods for one galaxy. The other two galaxies show 2-5$\sigma$ tension, depending on the dark matter contribution, when considering IMFs with a fixed low-mass cut-off of 0.08 Msol. Allowing a variable cut-off mass reduces the tension to 1-3$\sigma$ and can reach consistency with the lensing/dynamical $M_*/L$ if dark matter is assumed to be negligible. Compared to published scaling relations, the SNELLS lenses are distinctly offset to lower total $M/L$ and lighter IMFs than the mean matched-$\sigma$ ETG, as estimated from lensing and dynamics. However, their mean spectrum is virtually indistinguishable--at the 0.3% level--from the mean spectrum of matched-$\sigma$ ETGs drawn from the SDSS, and the derived IMF and abundance pattern are likewise consistent. This indicates a puzzling divergence between the masses and stellar population properties of the SNELLS sample. We discuss some possible resolutions.
The angular momentum distribution in dark matter haloes and galaxies is a key ingredient in understanding their formation. Especially, the internal distribution of angular momenta is closely related to the formation of disk galaxies. In this article, we use haloes identified from a high-resolution simulation, the Bolshoi simulation, to study the spatial distribution of specific angular momenta, $j(r,\theta)$. We show that by stacking haloes with similar masses to increase the signal-to-noise ratio, the profile can be fitted as a simple function, $j(r,\theta)=j_s \sin^2(\theta/\theta_s) (r/r_s)^2/(1+r/r_s)^4 $, with three free parameters, $j_s, r_s$, and $\theta_s$. Specifically, $j_s$ correlates with the halo mass $M_\mathrm{vir}$ as $j_s\propto M_\mathrm{vir}^{2/3}$, $r_s$ has a weak dependence on the halo mass as $r_s \propto M_\mathrm{vir}^{0.040}$, and $\theta_s$ is independent of $M_\mathrm{vir}$. This profile agrees with that from a rigid shell model, though its origin is unclear. Our universal specific angular momentum profile $j(r,\theta)$ is useful in modelling haloes' angular momenta. Furthermore, by using an empirical stellar mass - halo mass relation, we can infer the averaged angular momentum distribution of a dark matter halo. This is supported by the agreement between the maximum specific angular momentum predicted by our profile and those from observational data of disk galaxies.
Aims: We present the first measurement of the proper motion and orbit of the very distant and intriguing globular cluster NCG 2419. Methods: We have combined data from HST and Gaia DR1 to derive the relative proper motions of stars in the direction to the cluster. To tie to an absolute reference frame we have used a background galaxy located in the field. Results: We find the absolute proper motion of NGC 2419 to be $(\mu_{\alpha}\cos(\delta)$, $\mu_{\delta}$)=($-0.17\pm0.26,-0.49\pm0.17$) mas/yr. We have integrated the orbit of the cluster in a Galactic potential and found it to oscillate between $\sim$53 kpc and $\sim$98 kpc on a nearly polar orbit. This makes it very likely that NGC 2419 is a former cluster of the Sagittarius dwarf spheroidal galaxy, also because it shares the same sense of rotation around the Milky Way.
DIBs are ubiquitous in stellar spectra. Traditionally, they have been studied through their extraction from hot stars, because of their smooth continuum. In an era where there are several going-on or planned massive Galactic surveys using multi-object spectrographs, cool stars constitute an appealing set of targets. From the technical point of view, the extraction of DIBs in their spectra is more challenging due to the complexity of the continuum. In this contribution we will provide the community with an improved set of stellar lines in the spectral regions associated to the strong DIBs at l6196, l6269, l6284, and l6379. These lines will allow for the creation of better stellar synthetic spectra, reproducing the background emission and a more accurate extraction of the magnitudes associated with a given DIB. The Sun and Arcturus were used as representative examples of dwarf and giant stars, respectively. A high quality spectrum for each of them was modeled using TURBOSPECTRUM and the VALD stellar line list. The oscillator strength log(gf) and/or wavelength of specific lines were modified to create synthetic spectra where the residuals in both the Sun and Arcturus were minimized. The synthetic spectra based on the improved line lists reproduce the observed spectra for the Sun and Arcturus in the mentioned spectral ranges with greater accuracy. Residuals between the synthetic and observed spectra are always <10%, much better than with previously existing options. The new line list has been tested with some characteristic spectra, from a variety of stars, including both giant and dwarf stars, and under different degrees of extinction. As it happened with the Sun and Arcturus residuals in the fits used to extract the DIB information are smaller when using synthetic spectra made with the updated line lists. Tables with the updated parameters are provided to the community.
We present a comprehensive UBVRI and Washington CT1T2 photometric analysis of seven catalogued open clusters, namely: Ruprecht 3, 9, 37, 74, 150, ESO 324-15 and 436-2. The multi-band photometric data sets in combination with 2MASS photometry and Gaia astrometry for the brighter stars were used to estimate their structural parameters and fundamental astrophysical properties. We found that Ruprecht 3 and ESO 436-2 do not show self-consistent evidence of being physical systems. The remained studied objects are open clusters of intermediate-age (9.0 < log(t yr-1) < 9.6), of relatively small size (r_cls ~ 0.4 - 1.3 pc) and placed between 0.6 and 2.9 kpc from the Sun. We analized the relationships between core, half-mass, tidal and Jacoby radii as well as half-mass relaxation times to conclude that the studied clusters are in an evolved dynamical stage. The cluster masses obtained by summing those of the observed cluster stars resulted to be ~ 10-15 per cent of the masses of open clusters of similar age located closer than 2 kpc from the Sun. We found that cluster stars occupy volumes as large as those for tidally filled clusters.
We have analized a sample of 327 clusters of galaxies spanning the range 0.06-0.70 in redshift. Strong constraints on their mean intracluster emission by dust have been obtained using maps and catalogs from the HERSCHEL HerMES project; within a radius of 5 arcmin centered in each cluster, the 95% C.L. limits obtained are 86.6, 48.2 and 30.9 mJy at the observed frequencies of 250, 350 and 500 $\mu$m. From these restrictions, and assuming physical parameters typical of interstellar media in the Milky Way, we have obtained tight upper limits on the visual extinction of background galaxies due to the intracluster media: $A_V$(95% C.L.) <~$10^{-3}$ mags. Strong constraints are also obtained for the mass of such dust; for instance using the data at 350 $\mu$m we establish a 95% upper limit of $<10^9M_\odot$ within a circle with a radius of 5 arcmin centered in the clusters. This corresponds to a fraction of the total mass of the clusters of $9.5\times 10^{-6}$, and indicates a deficiency in the gas-to-dust ratio in the intracluster media by about three orders of magnitude as regards the value found in the Milky Way. Computing the total infrared luminosity of the clusters in three ranges of redshift (0.05-0.24, 0.24-0.42 and 0.42-0.71) and two ranges of mass ($<10^{14}$ and $>10^{14}M_\odot$) respectively, a strong evolution of luminosity in redshift ($L\sim z^{1.5}$) for both ranges of masses is found. The results indicate a strong declining in star formation rate with time in the last $\sim 6$ Gyr.
Local extremely metal-poor (XMP) galaxies are of particular astrophysical interest since they allow us to look into physical processes characteristic of the early Universe, from the assembly of galaxy disks to the formation of stars in conditions of low metallicity. Given the luminosity-metallicity relationship, all galaxies fainter than Mr < -13 are expected to be XMPs. Therefore, XMPs should be common in galaxy surveys. However, they are not, because several observational biases hamper their detection. This work compares the number of faint XMPs in the SDSS-DR7 spectroscopic survey with the expected number, given the known biases and the observed galaxy luminosity function. The faint end of the luminosity function is poorly constrained observationally, but it determines the expected number of XMPs. Surprisingly, the number of observed faint XMPs (around 10) is over-predicted by our calculation, unless the upturn in the faint end of the luminosity function is not present in the model. The lack of an upturn can be naturally understood if most XMPs are central galaxies in their low-mass dark matter halos, which are highly depleted in baryons due to interaction with the cosmic ultraviolet background and to other physical processes. Our result also suggests that the upturn towards low luminosity of the observed galaxy luminosity function is due to satellite galaxies.
We introduce the concept of a class of equivalence of molecular clouds represented by an abstract spherically symmetric, isotropic object. This object is described by use of abstract scales in respect to a given mass density distribution. Mass and average density are ascribed to each scale and thus are linked to the density distribution: a power-law type and an arbitrary continuous one. In the latter case, we derive a differential relationship between the mean density at a given scale and the structure parameter which defines the mass-density relationship. The two-dimensional (2D) projection of the cloud along the line of sight is also investigated. Scaling relations of mass and mean density are derived in the considered cases of power-law and arbitrary continuous distributions. We obtain relations between scaling exponents in the 2D and 3D cases. The proposed classes of equivalence are representative for the general structure of real clouds with various types of column-density distributions: power law, lognormal or combination of both.
We investigate radial gradients in the stellar initial mass function (IMF) in two early type galaxies using resolved measurements of several far red gravity sensitive absorption features, including the "Wing-Ford" band (FeH). We use the Oxford Short Wavelength Integral Field SpecTrogaph (SWIFT) to obtain resolved spectroscopic observations of NGC~1277 and IC~843, two galaxies with large central velocity dispersions and evidence for "heavy" IMFs from spectroscopic and dynamical measurements. Our observations cover the IMF sensitive features sodium \NaI, calcium triplet CaT as well as FeH, along with MgI 0.88 and TiO 0.89. We also use published optical indices to help untangle the degenerate parameters of age, metallicity, [$\alpha$/Fe] abundance and IMF slope. Within NGC~1277 we measure a flat FeH profile at $\sim$0.38\AA~with a strong [Na/Fe] gradient, from which we use stellar population models to infer an old, $\alpha$-enhanced population with a Chabrier IMF at all radii. IC~843 also displays a (slightly stronger) flat FeH profile at $\sim$0.4\AA, which together with optical indices suggests a similarly old, $\alpha$-enhanced population with a Chabrier IMF at all radii. Our results rule out bottom-heavy single power law IMFs in these objects and present galaxies which are in conflict with any simple IMF-$\sigma$ relationship.
The largest galaxies in the Universe reside in galaxy clusters. Using sensitive observations of carbon-monoxide, we show that the Spiderweb Galaxy -a massive galaxy in a distant protocluster- is forming from a large reservoir of molecular gas. Most of this molecular gas lies between the protocluster galaxies and has low velocity dispersion, indicating that it is part of an enriched inter-galactic medium. This may constitute the reservoir of gas that fuels the widespread star formation seen in earlier ultraviolet observations of the Spiderweb Galaxy. Our results support the notion that giant galaxies in clusters formed from extended regions of recycled gas at high redshift.
A model of key processes influencing the evolution of a hydrocarbon grain of an arbitrary size under astrophysical conditions corresponding to ionized hydrogen regions (HII regions) and supernova remnants is presented. The considered processes include aromatization and photodestruction, sputtering by electrons and ions, and shattering due to collisions between grains. The model can be used to simulate the grain size distribution and the aromatization degree during the evolution of HII regions and supernova remnants for a specified radiation field, relative velocity of gas and dust, etc. The contribution of various processes to the evolution of hydrocarbon dust grains for parameters typical for the interstellar medium of our Galaxy is presented. Small grains (less than 50 carbon atoms) should be fully aromatized in the general interstellar medium. If larger grains initially have an aliphatic structure, it is preserved to a substantial extent. Variations in the size distribution of the grains due to their mutual collisions depend appreciably on the adopted initial size distribution. For the MRN initial distribution a significant redistribution of grain sizes is obtained, which increases the mass fraction of smaller grains. Characteristic for an initial distribution from the work of Jones et al. (2013), with high initial fraction of small grains, is a general decrease in the number of grains of all sizes.
NASA's K2 mission is observing tens of thousands of stars along the ecliptic, providing data suitable for large scale asteroseismic analyses to inform galactic archaeology studies. Its first campaign covered a field near the north galactic cap, a region never covered before by large asteroseismic-ensemble investigations, and was therefore of particular interest for exploring this part of our Galaxy. Here we report the asteroseismic analysis of all stars selected by the K2 Galactic Archaeology Program during the mission's "North Galactic Cap" campaign 1. Our consolidated analysis uses six independent methods to measure the global seismic properties, in particular the large frequency separation, and the frequency of maximum power. From the full target sample of 8630 stars we find about 1200 oscillating red giants, a number comparable with estimates from galactic synthesis modeling. Thus, as a valuable by-product we find roughly 7500 stars to be dwarfs, which provide a sample well suited for galactic exoplanet occurrence studies because they originate from our simple and easily reproducible selection function. In addition, to facilitate the full potential of the data set for galactic archaeology we assess the detection completeness of our sample of oscillating red giants. We find the sample is at least near complete for stars with 40 < numax/microHz < 270, and numax_detec < 2.6*1e6 * 2e-Kp microHz. There is a detection bias against helium core burning stars with numax ~ 30 microHz, affecting the number of measurements of DeltaNu and possibly also numax. Although we can detect oscillations down to Kp = 15, our campaign 1 sample lacks enough faint giants to assess the detection completeness for stars fainter than Kp ~ 14.5.
The energy in turbulent flow can be amplified by compression, when the compression occurs on a timescale shorter than the turbulent dissipation time. This mechanism may play a part in sustaining turbulence in various astrophysical systems, including molecular clouds. The amount of turbulent amplification depends on the net effect of the compressive forcing and turbulent dissipation. By giving an argument for a bound on this dissipation, we give a lower bound for the scaling of the turbulent velocity with compression ratio in compressed turbulence. That is, turbulence undergoing compression will be enhanced at least as much as the bound given here, subject to a set of caveats that will be outlined. Used as a validation check, this lower bound suggests that some simulations and models of compressing astrophysical turbulence are too dissipative. The technique used highlights the relationship between compressed turbulence and decaying turbulence.
Many galaxy formation models predict alignments between galaxy spin and the cosmic web (i.e. the directions of filaments and sheets), leading to intrinsic alignment between galaxies that creates a systematic error in weak lensing measurements. These effects are often predicted to be stronger at high-redshifts ($z\gtrsim1$) that are inaccessible to massive galaxy surveys on foreseeable instrumentation, but IGM tomography of the Ly$\alpha$ forest from closely-spaced quasars and galaxies is starting to measure the $z\sim2-3$ cosmic web with the requisite fidelity. Using mock surveys from hydrodynamical simulations, we examine the utility of this technique, in conjunction with coeval galaxy samples, to measure alignment between galaxies and the cosmic web at $z\sim2.5$. We show that IGM tomography surveys with $\lesssim5$ $h^{-1}$ Mpc sightline spacing can accurately recover the eigenvectors of the tidal tensor, which we use to define the directions of the cosmic web. For galaxy spins and shapes, we use a model parametrized by the alignment strength, $\Delta\langle\cos\theta\rangle$, with respect to the tidal tensor eigenvectors from the underlying density field, and also consider observational effects such as errors in the galaxy position angle, inclination, and redshift. Measurements using the upcoming $\sim1\,\mathrm{deg}^2$ CLAMATO tomographic survey and 600 coeval zCOSMOS-Deep galaxies should place $3\sigma$ limits on extreme alignment models with $\Delta\langle\cos\theta\rangle\sim0.1$, but much larger surveys encompassing $>10,000$ galaxies, such as Subaru PFS, will be required to constrain models with $\Delta\langle\cos\theta\rangle\sim0.03$. These measurements will constrain models of galaxy-cosmic web alignment and test tidal torque theory at $z\sim2$, improving our understanding of the redshift dependence of galaxy-cosmic web alignment and the physics of intrinsic alignments.
We have extended the time baseline for observations of the proper motions of radio sources in the Orion BN/KL region from 14.7 to 22.5 years. We present improved determinations for the sources BN and I. In addition, we address the proper motions of the double radio source n, that have been questioned in the literature. We confirm that all three sources are moving away at transverse velocities of tens of km s$^{-1}$ from a region in-between them, where they were located about 500 years ago. Source n exhibits a new component that we interpret as due to a one-sided ejection of free-free emitting plasma that took place after 2006.36. We used the highly accurate relative proper motions between sources BN and I to determine that their closest separation took place in the year 1475$\pm$6, when they were within $\sim$100 AU or less from each other in the plane of the sky.
[abridged] In large-scale time-domain surveys, the processing of data, from procurement up to the detection of sources, is generally automated. One of the main challenges is contamination by artifacts, especially in regions of strong unresolved emission. We present a novel method for identifying candidates for variables and transients from the outputs of such surveys' data pipelines. We use the method to systematically search for novae in iPTF observations of the bulge of M31. We demonstrate that most artifacts produced by the iPTF pipeline form a locally uniform background of false detections approximately obeying Poissonian statistics, whereas genuine variables and transients as well as artifacts associated with bright stars result in clusters of detections, whose spread is determined by the source localization accuracy. This makes the problem analogous to source detection on images produced by X-ray telescopes, enabling one to utilize tools developed in X-ray astronomy. In particular, we use a wavelet-based source detection algorithm from the Chandra data analysis package CIAO. Starting from ~2.5x10^5 raw detections made by the iPTF data pipeline, we obtain ~4000 unique source candidates. Cross-matching these candidates with the source-catalog of a deep reference image, we find counterparts for ~90% of them. These are either artifacts due to imperfect PSF matching or genuine variable sources. The remaining ~400 detections are transient sources. We identify novae among these candidates by applying selection cuts based on the expected properties of nova lightcurves. Thus, we recovered all 12 known novae registered during the time span of the survey and discovered three nova candidates. Our method is generic and can be applied for mining any target out of the artifacts in optical time-domain data. As it is fully automated, its incompleteness can be accurately computed and corrected for.
The HASH (Hong Kong/ AAO/ Strasbourg/ H{\alpha}) planetary nebula research platform is a unique data repository with a graphical interface and SQL capability that offers the community powerful, new ways to undertake Galactic PN studies. HASH currently contains multi-wavelength images, spectra, positions, sizes, morphologies and other data whenever available for 2401 true, 447 likely, and 692 possible Galactic PNe, for a total of 3540 objects. An additional 620 Galactic post-AGB stars, pre-PNe, and PPN candidates are included. All objects were classified and evaluated following the precepts and procedures established and developed by our group over the last 15 years. The complete database contains over 6,700 Galactic objects including the many mimics and related phenomena previously mistaken or confused with PNe. Curation and updating currently occurs on a weekly basis to keep the repository as up to date as possible until the official release of HASH v1 planned in the near future.
Massive galaxy clusters are the most violent large scale structures undergoing merger events in the Universe. Based upon their morphological properties in X-rays, they are classified as un-relaxed and relaxed clusters and often host (a fraction of them) different types of non-thermal radio emitting components, viz., haloes, mini-haloes, relics and phoenix within their Intra Cluster Medium (ICM). The radio haloes show steep (alpha = -1.2) and ultra steep (alpha < -1.5) spectral properties at low radio frequencies, giving important insights on the merger (pre or post) state of the cluster. Ultra steep spectrum radio halo emissions are rare and expected to be the dominating population to be discovered via LOFAR and SKA in the future. Further, the distribution of matter (morphological information), alignment of hot X-ray emitting gas from the ICM with the total mass (dark + baryonic matter) and the bright cluster galaxy (BCG) is generally used to study the dynamical state of the cluster. We present here a multi wavelength study on 14 massive clusters from the CLASH survey and show the correlation between the state of their merger in X-ray and spectral properties (1.4 GHz - 150 MHz) at radio wavelengths. Using the optical data we also discuss about the gas-mass alignment, in order to understand the interplay between dark and baryonic matter in massive galaxy clusters.
This is the second paper in our series about the search for multiple populations in Magellanic Cloud star clusters using the Hubble Space Telescope. Here we report the detection of multiple stellar populations in the colour-magnitude diagrams of the intermediate-age clusters Lindsay 1, NGC 416 and NGC 339. With ages between 6.0 and 7.5 Gyr, these clusters are the youngest ones in which chemical abundance spreads have been detected so far. This confirms that the appearance of multiple populations is not restricted to only ancient globular clusters, but may also be a common feature in clusters as young as 6 Gyr. Our results are in agreement with a recent spectroscopic study of Lindsay 1. We found that the fraction of enriched stars in NGC 416 is ~45% whereas it is ~25% in NGC 339 and ~36% in Lindsay 1. Similar to NGC 121, these fractions are lower than the average value for globular clusters in the Milky Way.
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