We study the origin of the stellar $\alpha$-element-to-iron abundance ratio, $[\alpha/\mathrm{Fe}]_{\ast}$, of present-day central galaxies, using cosmological, hydrodynamical simulations from the Evolution and Assembly of GaLaxies and their Environments (EAGLE) project. For galaxies with stellar masses of $M_{\ast} > 10^{10.5}$ M$_{\odot}$, $[\alpha/\mathrm{Fe}]_{\ast}$ increases with increasing galaxy stellar mass and age. These trends are in good agreement with observations of early-type galaxies, and are consistent with a `downsizing' galaxy formation scenario: more massive galaxies have formed the bulk of their stars earlier and more rapidly, hence from an interstellar medium (ISM) that was mostly $\alpha$-enriched by massive stars. In the absence of feedback from active galactic nuclei (AGN), however, $[\alpha/\mathrm{Fe}]_{\ast}$ in $M_{\ast} > 10^{10.5}$ M$_{\odot}$ galaxies is roughly constant with stellar mass and decreases with mean stellar age, extending the trends found for lower-mass galaxies in both simulations with and without AGN. We conclude that AGN feedback can account for the $\alpha$-enhancement of massive galaxies, as it suppresses their star formation, quenching more massive galaxies at earlier times, thereby preventing the iron from longer-lived intermediate-mass stars (supernova Type Ia) from being incorporated into younger stars.
Gravitational waves (GWs) provide a revolutionary tool to investigate yet unobserved astrophysical objects. Especially the first stars, which are believed to be more massive than present-day stars, might be indirectly observable via the merger of their compact remnants. We develop a self-consistent, cosmologically representative, semi-analytical model to simulate the formation of the first stars and track the binary stellar evolution of the individual systems until the coalescence of the compact remnants. We estimate the contribution of primordial stars to the intrinsic merger rate density and to the detection rate of the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO). Owing to their higher masses, the remnants of primordial stars produce strong GW signals, even if their contribution in number is relatively small. We find a probability of $\sim 1\%$ that the current detection GW150914 is of primordial origin. We estimate that aLIGO will detect roughly 1 primordial BH-BH merger per year for the final design sensitivity, although this rate depends sensitively on the primordial initial mass function. Turning this around, the detection of black hole mergers with a total binary mass of $\sim 300\,\mathrm{M}_\odot$ would enable us to constrain the primordial initial mass function.
We present post-cryogenic Spitzer imaging at 3.6 and 4.5 micron with the Infrared Array Camera (IRAC) of the Spitzer/HETDEX Exploratory Large-Area (SHELA) survey. SHELA covers $\sim$deg$^2$ of the Sloan Digital Sky Survey "Stripe 82" region, and falls within the footprints of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) and the Dark Energy Survey. The HETDEX blind R $\sim$ 800 spectroscopy will produce $\sim$ 200,000 redshifts from the Lyman-$\alpha$ emission for galaxies in the range 1.9 < z < 3.5, and an additional $\sim$200,000 redshifts from the [OII] emission for galaxies at z < 0.5. When combined with deep ugriz images from the Dark Energy Camera, K-band images from NEWFIRM, and other ancillary data, the IRAC photometry from Spitzer will enable a broad range of scientific studies of the relationship between structure formation, galaxy stellar mass, halo mass, AGN, and environment over a co-moving volume of $\sim$0.5 Gpc$^3$ at 1.9 < z < 3.5. Here, we discuss the properties of the SHELA IRAC dataset, including the data acquisition, reduction, validation, and source catalogs. Our tests show the images and catalogs are 80% (50%) complete to limiting magnitudes of 22.0 (22.6) AB mag in the detection image, which is constructed from the weighted sum of the IRAC 3.6 and 4.5 micron images. The catalogs reach limiting sensitivities of 1.1 $\mu$Jy at both 3.6 and 4.5 micron (1$\sigma$, for R=2 arcsec circular apertures). As a demonstration of science, we present IRAC number counts, examples of highly temporally variable sources, and galaxy surface density profiles of rich galaxy clusters. In the spirit of Spitzer Exploratory programs we provide all images and catalogs as part of the publication.
With current space-based missions it is now possible to obtain age-sensitive asteroseismic information for tens of thousands of red giants. This provides a promising opportunity to study the Galactic structure and evolution. We use asteroseismic data of red giants, observed by Kepler, to test the current theoretical framework of modelling the Galaxy based on population synthesis modeling and the use of asteroseismic scaling relations for giants. We use the open source code Galaxia to model the Milky Way and find the distribution of the masses predicted by Galaxia to be systematically offset with respect to the seismically-inferred observed masses. The Galactic model overestimates the number of low mass stars, and these stars are predominantly old and of low metallicity. Using corrections to the $\Delta \nu$ scaling relation suggested by stellar models (available for download) significantly reduces the disagreement between predicted and observed masses. For a few cases where non-seismic mass estimates are available, the corrections to $\Delta \nu$ also improve the agreement between seismic and non-seismic mass estimates. The disagreement between predictions of the Galactic model and the observations is most pronounced for stars with ${\rm [Fe/H]}<-0.5$ and ${\rm [Fe/H]}>0$ or for $T_{\rm eff}>4700$ K. Altering the star formation rate in order to suppress stars older than 10 Gyr improves the agreement for mass but leads to inconsistent color distributions. We also tested the predictions of the TRILEGAL Galactic model. However, unlike {\sl Galaxia}, it had difficulties in reproducing the photometric properties of the Kepler Input Catalog because it overestimates the number of blue stars. We conclude that either the scaling relations and/or the Galactic models need to be revised to reconcile predictions of theory with asteroseismic observations.
Understanding how galaxies form in the early universe and their subsequent evolution through cosmic time is a major goal of modern astrophysics. Panchromatic look-back sky surveys significantly advanced the field in the past decades, and we are now entering an even more fruitful period - a 'golden age' of radio astronomy - with upgraded, and new facilities delivering an order of magnitude increase in sensitivity. An overview of recent developments in radio continuum sky surveys, focusing on the physical properties and cosmic evolution of radio AGN since z~5 is presented here.
We study the fragmentation of the most nearby high line-mass filament, the integral shaped filament (ISF) in the Orion A molecular cloud. We have observed a 1.6 pc long section of the ISF with the Atacama Large Millimetre/submillimeter Array (ALMA) at 3 mm continuum emission, at a resolution of $\sim$3" (1$\,$200 AU). We identify from the region 40 dense cores with masses on the order of a solar mass. The nearest neighbour separation distribution of the cores does not show a preferred fragmentation scale; the frequency of short separations increases down to our resolution limit. We apply a two-point correlation analysis on the dense core separations and show that the cores are significantly grouped at separations below $\sim$17$\,$000 AU and strongly grouped below $\sim$6$\,$000 AU. In addition, the two-point correlation function indicates periodic grouping of the cores into groups of $\sim$30$\,$000 AU in size, separated by $\sim$55$\,$000 AU. The groups coincide with dust column density peaks detected by Herschel. These results suggest a two-mode fragmentation in which the maternal filament periodically fragments into groups of dense cores. The strong increase of separations below 6$\,$000 AU may be related to the regime of significant core-to-core interactions. We also find that the protostars in the northern ISF are grouped at separations below $\sim$17$\,$000 AU. The stars with disks do not show significant grouping in the ALMA-covered region. This suggests that the grouping of dense cores is partially retained over the protostar lifetime, but not over the lifetime of stars with disks. This is in agreement with protostars being ejected from the maternal filament by the slingshot mechanism, a model recently proposed for the ISF by Stutz & Gould. The separation distributions of the dense cores and protostars may also provide an evolutionary tracer of filament fragmentation.
OH megamasers (OHMs) are rare, luminous molecular masers that are typically
observed in (ultra) luminous infrared galaxies and serve as markers of major
galaxy mergers. In blind emission line surveys such as the Arecibo Legacy Fast
Arecibo L-Band Feed Array (ALFALFA) survey for neutral hydrogen (HI), OHMs at
z~0.2 can mimic z~0.05 HI lines. We present the results of optical spectroscopy
of ambiguous HI detections in the ALFALFA 40% data release detected by the Wide
Field Infrared Survey Explorer (WISE) but with uncertain optical counterparts.
The optical redshifts, obtained from observations at the Apache Point
Observatory, revealed five new OHMs and identified 129 HI optical counterparts.
Sixty candidates remain ambiguous. The new OHMs are the first detected in a
blind spectral line survey.
The number of OHMs in ALFALFA is consistent with predictions from the OH
luminosity function. Additionally, the mid-infrared magnitudes and colors of
the OHM host galaxies found in a blind survey do not seem to differ from those
found in previous targeted surveys. This validates the methods used in previous
IR-selected OHM surveys and indicates there is no previously unknown
OHM-producing population at z~0.2. We also provide a method for future surveys
to separate OH megamasers from 99% of HI line emitters without optical
spectroscopy by using WISE infrared colors and magnitudes. Since the fraction
of OHMs found in flux-limited HI surveys is expected to increase with the
survey's redshift, this selection method can be applied to future flux-limited
high-redshift hydrogen surveys.
Gravity plays important roles in the evolution of molecular clouds. We present an acceleration mapping method to estimate the acceleration induced by gravitational interactions in molecular clouds based on observational data. We find that the geometry of a region has a significant impact on the behavior of gravity. In the Pipe nebula which can be approximated as a gas filament, we find that gravitational acceleration can effectively compress the end of this filament, which may have triggered star formation. We identify this as the "gravitational focusing" effect proposed by Burkert & Hartman (2004). In the sheet-like IC348-B3 region, gravity can lead to collapse at its edge, while in the centrally condensed NGC1333 cluster-forming region gravity can drive accretion towards the center. In general, gravitational acceleration tends to be enhanced in the localized regions around the ends of the filaments and the edges of sheet-like structures. Neglecting magnetic fields, these "gravitational focusing" and "edge collapse" effects can promote the formation of dense gas in a timescale that is much shorter than the global dynamical time. Since the interstellar medium is in general structured, these edge effects should be prevalent.
We find that significant incompleteness in stellar number counts results in a significant overestimate of the microlensing optical depth $\tau$ and event rate per star per year $\Gamma$ toward the Galactic bulge from the first two years of MOA-II survey. We find that the completeness in Red Clump Giant (RCG) counts $f_{\rm RC}$ decreases proportional to the galactic latitude $b$, as $f_{\rm RC}=(0.63\pm0.11)-(0.052\pm0.028)\times b$, ranging 1-0.7 at $b=-6^\circ\sim-1.5^\circ$. This caused overestimates in $\tau$ and $\Gamma$. The previous measurements with all source by Difference Image Analysis (DIA) by MACHO and MOA-I suffer the same bias due to their relatively poor seeing. On the other hand, the measurements with RCG sample by OGLE-II, MACHO and EROS were free from this bias because they seldomected only the events associated to the resolved stars. Thus, the incompleteness both in the number of events and stellar number count cancel out. We estimate $\tau$ and $\Gamma$ by correcting this incompleteness. In the central fields with $|l|< 5^\circ$, we find an event rates of $\Gamma= [18.74\pm 0.91]\times10^{-6} \exp[(0.53\pm 0.05)(3-|b|)]$ star$^{-1}$ yr$^{-1}$ and an optical depth (for events with $t_{\rm E}\leq 200 $days) of $\tau_{200}= [1.84\pm 0.14]\times10^{-6} \exp[(0.44\pm 0.07)(3-|b|)]$ for the 427 events using all sources brighter than $I_s \leq 20$ mag. Our revised all-source sample optical depth measurements are about 2-$\sigma$ smaller than the other measurements with all-source and consistent with the RCG measurement from OGLE-II, MACHO and EROS within 1-$\sigma$. We conclude that the long-standing problem on discrepancy between the high optical depth with all source by DIA and low optical depth with RCG sample can be explained by the incompleteness of the stellar number count.
We present the results obtained with MUSE on the core of the lensing cluster A1689. Integral-field observations with MUSE provide a unique view of the central region, allowing us to conduct a complete census on both cluster galaxies and lensed background sources, identified based on their spectral features without preselection. We investigate the multiple-image configuration for all known sources in the field. Previous to our survey, 28 different lensed galaxies displaying 46 multiple images were known in the MUSE field of view, most of them based on photometric redshifts and lensing considerations. Among them, we spectroscopically confirm 12 images based on their emission-lines, corresponding to 7 different lensed galaxies between z = 0.95 and 5.0. In addition, 14 new galaxies have been spectroscopically identified in this area, with redshifts ranging between 0.8 and 6.2. All background sources within the MUSE field of view correspond to multiple-imaged systems lensed by A1689. 17 sources in total are found at z > 3 based on their Lyman-alpha emission, with Lyman-alpha luminosities ranging between 40.5 < log(Ly{\alpha}) < 42.5 after correction for magnification. This sample is particularly sensitive to the slope of the LF toward the faintest-end. The density of sources obtained in this survey is consistent with a steep value of {\alpha} < -1.5, although this result still needs further investigation. These results illustrate the efficiency of MUSE in the characterization of lensing clusters on one hand, and the study of faint and distant populations of galaxies on the other hand. In particular, our current survey of lensing clusters should provide a unique census of sources responsible for the reionization in a representative volume at z ~ 4-7.
We observed high S/N, high velocity resolution NH$_3$(1,1) and (2,2) emission on an extended map in TMC-1, a filamentary cloud in a nearby quiescent star forming area. By fitting multiple hyperfine-split line profiles to the NH$_3$(1,1) spectra we derived the velocity distribution of the line components and calculated gas parameters on several positions. Herschel SPIRE continuum observations were reduced and used to calculate the physical parameters of the Planck Galactic Cold Clumps in the region. The Herschel-based column density map of TMC-1 shows a main ridge with two local maxima and a separated peak to the south-west. H$_2$-column densities and dust temperatures are in the range of 0.5-3.3 $\times$ 10$^{22}$ cm$^{-2}$ and 10.5-12 K, respectively. NH$_3$-column densities are 2.8-14.2 $\times$ 10$^{14}$ cm$^{-2}$ and and H$_2$-volume densities are 0.4-2.8 $\times$ 10$^4$ cm$^{-3}$. Kinetic temperatures are typically very low with a minimum of 9 K, and a maximum of 13.7 K was found at the Class I protostar IRAS 04381+2540. The kinetic temperatures vary similarly as the dust temperatures in spite of the fact that densities are lower than the critical density for coupling between the gas and dust phase. The k-means clustering method separated four sub-filaments in TMC-1 in the position-velocity-column density parameter space. They have masses of 32.5, 19.6, 28.9 and 45.9 M$_{\odot}$, low turbulent velocity dispersion (0.13-0.2 kms$^{-1}$) and they are close to gravitational equilibrium. We label them TMC-1F1 through F4. TMC-1F1, TMC-1F2 and TMC-1F4 are very elongated, dense and cold. TMC-1F3 is a little less elongated and somewhat warmer, probably heated by IRAS 04381+2540 that is embedded in it. TMC-1F3 is $\approx$ 0.1 pc behind TMC1-F1. Because of its structure, TMC-1 is a good target to test filament evolution scenarios.
This paper explores the possibility of determining the spin of the supermassive black hole (SMBH) in Sgr A*, by using secondary images of stars orbiting the SMBH. The photons propagate close to the SMBH and their trajectories probe the space time in a region where the spin of the SMBH is important. We find the appearance of spikes in the secondary image, which depends on the angular momentum and spin axis of the SMBH and study the specific case of the star S2 in detail. The spikes has a magnitude of $\sim 29$ in the K-band and the required angular resolution is of order 15-20 $\mu$as. The combination of these two requirements poses an extreme observational challenge, but might be possible with interferometric observations in the sub-mm regime. The next possible time frame for observing this effect on the star S2 is in the late 2017 and then it repeats with the period of the star.
NGC 1808 is a nearby barred starburst galaxy with an outflow from the nuclear region. To study the inflow and outflow processes related to star formation and dynamical evolution of the galaxy, we have carried out \(^{12}\)CO (\(J=1-0\)) mapping observations of the central \(r\sim4\) kpc of NGC 1808 using the Atacama Large Millimeter/submillimeter Array (ALMA). Four distinct components of molecular gas are revealed at high spatial resolution of 2\arcsec (\(\sim100\) pc): (1) a compact (\(r<200\) pc) circumnuclear disk (CND), (2) \(r\sim500\) pc ring, (3) gas-rich galactic bar, and (4) spiral arms. Basic geometric and kinematic parameters are derived for the central 1-kpc region using tilted-ring modeling. The derived rotation curve reveals multiple mass components that include (1) a stellar bulge, (2) nuclear bar and molecular CND, and (3) unresolved massive (\(\sim10^7~M_\sun\)) core. Two systemic velocities, 998 km s\(^{-1}\) for the CND and 964 km s\(^{-1}\) for the 500-pc ring, are revealed, indicating a kinematic offset. The pattern speed of the primary bar, derived by using a cloud-orbit model, is \(56\pm11\) km s\(^{-1}\) kpc\(^{-1}\). Non-circular motions are detected associated with a nuclear spiral pattern and outflow in the central 1-kpc region. The ratio of the mass outflow rate to the star formation rate is \(\dot{M}_\mathrm{out}/SFR\sim0.2\) in the case of optically thin CO (1-0) emission in the outflow, suggesting low efficiency of star formation quenching.
NGC 2264-C is a high-mass protocluster where several star-formation events are known to have occurred. To investigate whether past protostellar activity has left a chemical imprint in this region, we mapped it in SiO($J = 2-1$), a shock tracer, and several other molecular lines with the Nobeyama 45 m telescope. Our observations show the presence of a complex network of protostellar outflows. The strongest SiO emission lies beyond a radius of $\sim 0.1$ pc with respect to the center of the clump, and is characterized by broad ($> 10$ km s$^{-1}$) lines and abundances of $\sim 1.4 \times 10^{-8}$ with respect to H$_2$. Interestingly, SiO appears relatively depleted ($\chi_\mathrm{SiO} \sim 4 \times 10^{-9}$) within this radius, despite it being affected by molecular outflow activity. We attribute this to fast condensation of SiO back onto dust grains and/or rapid gas-phase destruction of SiO, favored by the high density present in this area ($> 10^6$ cm$^{-3}$). Finally, we identify a peripheral, narrow-line ($\sim 2$ km s$^{-1}$) component, where SiO has an abundance of a few times 10$^{-11}$. After considering different options, we conclude that this weak emission may be tracing protostellar shocks from the star formation episode that preceded the current one, which have decelerated over time and eventually resulted in SiO being largely depleted/destroyed. Alternatively, a population of unresolved low-mass protostars may be responsible for the narrow SiO emission. High-angular resolution observations are necessary to distinguish between these two possibilities and thus understand the role of SiO as a chemical tracer of past star-formation episodes in massive protoclusters.
The ExoMol database (www.exomol.com) provides extensive line lists of molecular transitions which are valid over extended temperatures ranges. The status of the current release of the database is reviewed and a new data structure is specified. This structure augments the provision of energy levels (and hence transition frequencies) and Einstein $A$ coefficients with other key properties, including lifetimes of individual states, temperature-dependent cooling functions, Land\'e $g$-factors, partition functions, cross sections, $k$-coefficients and transition dipoles with phase relations. Particular attention is paid to the treatment of pressure broadening parameters. The new data structure includes a definition file which provides the necessary information for utilities accessing ExoMol through its application programming interface (API). Prospects for the inclusion of new species into the database are discussed.
Low-mass, variable, high-velocity stars are interesting study cases for many aspects of Galactic structure and evolution. Until recently, the only known high- or hyper-velocity stars were young stars thought to originate from the Galactic centre. Wide-area surveys like APOGEE and BRAVA have found several low-mass stars in the bulge with Galactic rest-frame velocities larger than 350 km/s. In this study we present the first abundance analysis of a low-mass, RR Lyrae star, located close to the Galactic bulge, with a space motion of ~ -400 km/s. Using medium-resolution spectra, we derive abundances (including upper limits) of 11 elements. These allow us to chemically tag the star and discuss its origin, although our derived abundances and metallicity, at [Fe/H] =-0.9 dex, do not point toward one unambiguous answer. Based on the chemical tagging, we cannot exclude that it originated in the bulge. However, combining its retrograde orbit and the derived abundances suggests that the star was accelerated from the outskirts of the inner (or even outer) halo during many-body interactions. Other possible origins include the bulge itself, or the star could be stripped from a star cluster or the Sagittarius dwarf galaxy when it merged with the Milky Way.
We present a deep centimeter-wavelength catalog of the Orion Nebula Cluster (ONC), based on a 30h single-pointing observation with the Karl G. Jansky Very Large Array in its high-resolution A-configuration using two 1 GHz bands centered at 4.7 GHz and 7.3 GHz. A total of 556 compact sources were detected in a map with a nominal rms noise of 3 muJy/bm, limited by complex source structure and the primary beam response. Compared to previous catalogs, our detections increase the sample of known compact radio sources in the ONC by more than a factor of seven. The new data show complex emission on a wide range of spatial scales. Following a preliminary correction for the wideband primary-beam response, we determine radio spectral indices for 170 sources whose index uncertainties are less than +/-0.5. We compare the radio to the X-ray and near-infrared point-source populations, noting similarities and differences.
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We present a study of the optical properties of the 26 most massive galaxy clusters selected within the SPT-SZ 2500 deg$^2$ survey. This Sunyaev-Zel'dovich effect selected sample spans a redshift range of 0.10 < z < 1.13. We measure the galaxy radial profile, the luminosity function (LF), and the halo occupation number (HON) using optical data with a typical depth of $m^*$ + 2. The stacked radial profiles are consistent with a NFW profile with a concentration of $2.84^{+0.40}_{-0.37}$ for the red sequence (RS) and $2.36^{+0.38}_{-0.35}$ for the total population. Stacking the data in multiple redshift bins shows a hint of redshift evolution in the concentration when both the total population is used, and when only RS galaxies are used (at 2.1$\sigma$ and 2.8$\sigma$, respectively). The stacked LF shows a faint end slope $\alpha = -1.06^{+0.04}_{-0.03}$ for the total and $\alpha = -0.80^{+0.04}_{-0.03}$ for the RS population. The redshift evolution of $m^*$ is found to be consistent with a passively evolving Composite Stellar Population (CSP) model. By adopting the CSP model predictions, we explore the redshift evolution of the schechter parameters $\alpha$ and $\phi^*$. We find $\alpha$ for the total population to be consistent with no evolution (0.3$\sigma$), while evidence of evolution for the red galaxies is mildly significant (1.1-2.1$\sigma$). The data show that the density $\phi^*$/E$^2$(z) decreases with redshift, in tension with the self-similar expectation at a 2.4$\sigma$ level for the total population. The measured HON-mass relation has a lower normalization than previous studies at low redshift. Finally, our data support HON redshift evolution at a 2.1$\sigma$ level, with clusters at higher redshift containing fewer galaxies per unit mass to $m^*$ + 3 than their low-z counterparts [abridged].
We introduce a series of cosmological hydrodynamical simulations of Lstar (M_200 =10^11.7 - 10^12.3 Msol) and group-sized (M_200 = 10^12.7 - 10^13.3 Msol) haloes run with the model used for the EAGLE project, which additionally includes a non-equilibrium ionization and cooling module that follows 136 ions. The simulations reproduce the observed correlation, revealed by COS-Halos at z~0.2, between O VI column density at impact parameters b < 150 kpc and the specific star formation rate (sSFR=SFR/Mstar) of the central galaxy at z~0.2. We find that the column density of circumgalactic O VI is maximal in the haloes associated with Lstar galaxies, because their virial temperatures are close to the temperature at which the ionization fraction of O VI peaks (T~10^5.5 K). The higher virial temperature of group haloes (> 10^6 K) promotes oxygen to higher ionization states, suppressing the O VI column density. The observed NO VI-sSFR correlation therefore does not imply a causal link, but reflects the changing characteristic ionization state of oxygen as halo mass is increased. In spite of the mass-dependence of the oxygen ionization state, the most abundant circumgalactic oxygen ion in both Lstar and group haloes is O VII; O VI accounts for only 0.1% of the oxygen in group haloes and 0.9-1.3% with Lstar haloes. Nonetheless, the metals traced by O VI absorbers represent a fossil record of the feedback history of galaxies over a Hubble time; their characteristic epoch of ejection corresponds to z > 1 and much of the ejected metal mass resides beyond the virial radius of galaxies. For both Lstar and group galaxies, more of the oxygen produced and released by stars resides in the circumgalactic medium (within twice the virial radius) than in the stars and ISM of the galaxy.
The extensive ground-based spectroscopy campaign from the VIMOS Ultra-Deep Survey (VUDS), and the deep multi-wavelength photometry in three very well observed extragalactic fields (ECDFS, COSMOS, VVDS), allow us to investigate physical properties of a large sample (~4000 galaxies) of spectroscopically confirmed faint (i_{AB}<~25 mag) star-forming galaxies, with and without Lyman alpha in emission, at z~2-6. The fraction of Lyman alpha emitters (LAEs; equivalent width (EW)=>20A) increases from ~10% at z~2 to ~40% at z~5-6, which is consistent with previous studies that employ higher Lyman alpha EW cut. This increase in the LAE fraction could be, in part, due to a decrease in the dust content of galaxies as redshift increases. When we compare best-fit SED estimated stellar parameters for LAEs and non-LAEs, we find that E(B-V) is smaller for LAEs at all redshifts and the difference in the median E(B-V) between LAEs and non-LAEs increases as redshift increases, from 0.05 at z~2 to 0.1 at z~3.5 to 0.2 at z~5-6. For the luminosities probed here (~L*), we find that star formation rates (SFRs) and stellar masses of galaxies, with and without Lyman alpha in emission, show small differences such that, LAEs have lower SFRs and stellar masses compared to non-LAEs. This result could be a direct consequence of the sample selection. Our sample of LAEs are selected based on their continuum magnitudes and they probe higher continuum luminosities compared to narrow-band/emission line selected LAEs. Based on our results, it is important to note that all LAEs are not universally similar and their properties are strongly dependent on the sample selection, and/or continuum luminosities.
Recently, a class of non-truncated radially-anisotropic models (the so-called $f^{(\nu)}$-models), originally constructed in the context of violent relaxation and modeling of elliptical galaxies, has been found to possess interesting qualities in relation to observed and simulated globular clusters. In view of new applications to globular clusters, we improve this class of models along two directions. To make them more suitable for the description of small stellar systems hosted by galaxies, we introduce a 'tidal' truncation (by means of a procedure that guarantees full continuity of the distribution function). The new $f_T^{(\nu)}$-models are shown to provide a better fit to the observed photometric and spectroscopic profiles for a sample of 13 globular clusters studied earlier by means of non-truncated models; interestingly, the best-fit models also perform better with respect to the radial-orbit instability. Then we design a flexible but simple two-component family of truncated models, to study the separate issues of mass segregation and of multiple populations. We do not aim at a fully realistic description of globular clusters, to compete with the description currently obtained by means of dedicated simulations. The goal here is to try to identify the simplest models, that is, those with the smallest number of free parameters, but still able to provide a reasonable description for clusters that are evidently beyond the reach of one-component models: with this tool we aim at identifying the key factors that characterize mass segregation or the presence of multiple populations. To reduce the relevant parameter space, we formulate a few physical arguments (based on recent observations and simulations). A first application to two well-studied globular clusters is briefly described and discussed.
We study the composition of the faint radio population selected from the VLA-COSMOS 3GHz Large Project, a radio continuum survey performed at 10 cm wavelength. The survey covers the full 2 square degree COSMOS field with mean $rms\sim2.3$ $\mu$Jy/beam, cataloging 10,899 source components above $5\times rms$. By combining these radio data with UltraVISTA, optical, near-infrared, and Spitzer/IRAC mid-infrared data, as well as X-ray data from the Chandra Legacy, and Chandra COSMOS surveys, we gain insight into the emission mechanisms within our radio sources out to redshifts of $z\sim5$. From these emission characteristics we classify our souces as star forming galaxies or AGN. Using their multi-wavelength properties we further separate the AGN into sub-samples dominated by radiatively efficient and inefficient AGN, often referred to as high- and low-excitation emission line AGN. We compare our method with other results based on fitting of the sources' spectral energy distributions using both galaxy and AGN spectral models, and those based on the infrared-radio correlation. We study the fractional contributions of these sub-populations down to radio flux levels of $\sim$10 $\mu$Jy. We find that at 3 GHz flux densities above $\sim$400 $\mu$Jy quiescent, red galaxies, consistent with the low-excitation radio AGN class constitute the dominant fraction. Below densities of $\sim$200 $\mu$Jy star-forming galaxies begin to constitute the largest fraction, followed by the low-excitation, and X-ray- and IR-identified high-excitation radio AGN.
We present an in depth study on the evolution of galaxy properties in compact groups over the past 3 Gyr. We are using the largest multi-wavelength sample to-date, comprised 1770 groups (containing 7417 galaxies), in the redshift range of 0.01<z<0.23. To derive the physical properties of the galaxies we rely on ultraviolet (UV)-to-infrared spectral energy distribution modeling, using CIGALE. Our results suggest that during the 3 Gyr period covered by our sample, the star formation activity of galaxies in our groups has been substantially reduced (3-10 times). Moreover, their star formation histories as well as their UV-optical and mid-infrared colors are significantly different from those of field and cluster galaxies, indicating that compact group galaxies spend more time transitioning through the green valley. The morphological transformation from late-type spirals into early-type galaxies occurs in the mid-infrared transition zone rather than in the UV-optical green valley. We find evidence of shocks in the emission line ratios and gas velocity dispersions of the late-type galaxies located below the star forming main sequence. Our results suggest that in addition to gas stripping, turbulence and shocks might play an important role in suppressing the star formation in compact group galaxies.
We explore the possibility of observing Population III (Pop~III) stars, born
of the primordial gas.
Pop~III stars with masses below $0.8 M_\odot$ should survive to date though
are not observed yet, but the existence of stars with low metallicity as
[Fe/H]$ < -5$ in the Milky Way halo suggests the surface pollution of Pop~III
stars with accreted metals from the interstellar gas after birth. In this
paper, we investigate the runaway of Pop~III stars from their host mini-halos,
considering the ejection of secondary members from binary systems when their
massive primaries explode as supernovae.
These stars save them from the surface pollution.
By computing the star formation and chemical evolution along with the
hierarchical structure formation based on the extended Press--Schechter merger
trees, we demonstrate that several hundreds to tens of thousands of low-mass
Pop~III stars escape from the building blocks of the Milky Way.
The second and later generations of extremely metal-poor (EMP) stars are also
escaped from the mini-halos.
We discuss the spatial distributions of these escaped stars by evaluating the
distances between the mini-halos in the branches of merger trees under the
spherical collapse model of dark matter halos.
It is demonstrated that the escaped stars distribute beyond the stellar halo
with a density profile close to the dark matter halo, while the Pop~III stars
are slightly more centrally concentrated .
Some escaped stars leave the Milky Way and spread into the intergalactic
space.
Based on the results, we discuss the feasibility of observing the Pop~III
stars with the pristine surface abundance.
A review of the current challenges for the understanding of the physics of extragalactic radio jets from supermassive black holes is presented. Also, a prospect is given about how both very long baseline interferometry (VLBI) and polarimetric observations help us to understand their physics and the ones of their magnetic fields. This paper focuses on the impact that previous ultra-high resolution polarimetric surveys have had on our current knowledge on radio loud AGN. It first concentrates on the expectations about the improvement that the Square Kilometer Array, used as a super-sensitive VLBI station on existing and future very long baseline interferometric arrays, will provide in terms of access to new source classes, and in terms of a deeper portion of the Universe than currently accessible. A series of key new radio loud AGN science fields, to be opened by the Square Kilometer Array, are outlined together with a collection of preliminary ideas about possible programs of interest to deep in such fields. The complementary aspects of future super-sensitive VLBI observations as compared to deep continuum surveys with the Square Kilometer Array and its precursors are also outlined here.
We developed a hierarchical Bayesian model (HBM) to investigate how the presence of Seyfert activity relates to their environment, herein represented by the galaxy cluster mass, $M_{200}$, and the normalized cluster centric distance, $r/r_{200}$. We achieved this by constructing an unbiased sample of galaxies from the Sloan Digital Sky Survey, with morphological classifications provided by the Galaxy Zoo Project. A propensity score matching approach is introduced to control for the effects of confounding variables: stellar mass, galaxy colour, and star formation rate. The connection between Seyfert-activity and environmental properties in the de-biased sample is modelled within a HBM framework using the so-called logistic regression technique, suitable for the analysis of binary data (e.g., whether or not a galaxy hosts an AGN). Unlike standard ordinary least square fitting methods, our methodology naturally allows modelling the probability of Seyfert-AGN activity in galaxies on their natural scale, i.e. as a binary variable. Furthermore, we demonstrate how a HBM can incorporate information of each particular galaxy morphological type in an unified framework. In elliptical galaxies our analysis indicates a strong correlation of Seyfert-AGN activity with $r/r_{200}$, and a weaker correlation with the mass of the host. In spiral galaxies these trends do not appear, suggesting that the link between Seyfert activity and the properties of spiral galaxies are independent of the environment.
We present the peculiar in-plane velocities derived from the LAMOST red clump stars. From the variations of the in-plane velocity with the Galactocentric radius for the young and old red clump stars, we are able to identify two types of peculiar velocities: 1) both the two red clump populations show that the radial velocity is negative within $R=9.0$\,kpc and becomes positive beyond (denoted as the \emph{long-wave} mode); and 2) the young red clump stars show larger mean radial velocity than the old population by about 3\,km$\rm s^{-1}$ between $R=9$ and 12\,kpc (denoted as the \emph{short-wave} mode). We find that the elliptical disk induced by the rotating bar can well explain the \emph{long-wave} mode peculiar velocity. The axis ratio of the elliptical disk is around 0.8-0.95 and the disk keeps circular at $R=9.24\pm0.2$\,kpc, which should be the location of the outer Lindblad resonance radius (OLR). Adopting the circular speed of 238\,km$\rm s^{-1}$, the pattern speed of the bar is then derived as $48\pm3$\,km$\rm s^{-1}$kpc$^{-1}$ from the location of OLR. On the other hand, the \emph{short-wave} mode is likely the perturbation of the spiral arms as density waves.
We present the first detailed integral field spectroscopy study of nine
central void galaxies with M*>10^10 Msun using the Wide Field Spectrograph
(WiFeS) to determine how a range of assembly histories manifest themselves in
the current day Universe. While the majority of these galaxies are evolving
secularly, we find a range of morphologies, merger histories and stellar
population distributions, though similarly low Halpha-derived star formation
rates (<1 Msun/yr). Two of our nine galaxies host AGNs, and two have kinematic
disruptions to their gas that are not seen in their stellar component. Most
massive void galaxies are red and discy, which we attribute to a lack of major
mergers. Some have disturbed morphologies and may be in the process of evolving
to early-type thanks to ongoing minor mergers at present times, likely fed by
tendrils leading off filaments. The diversity in our small galaxy sample,
despite being of similar mass and environment means that these galaxies are
still assembling at present day, with minor mergers playing an important role
in their evolution.
We compare our sample to a mass and magnitude-matched sample of field
galaxies, using data from the Sydney-AAO Multi-object Integral field
spectrograph (SAMI) galaxy survey. We find that despite environmental
differences, galaxies of mass M*>10^10 Msun have similarly low star formation
rates (<3 Msun/yr). The lack of distinction between the star formation rates of
the void and field environments points to quenching of massive galaxies being a
largely mass-related effect.
We use near infrared integral field unit (IFU) spectroscopy to search for H$\alpha$ emission associated with star formation in a sample of 28 heavily reddened ($E(B-V)\simeq$0.5-1.9), hyperluminous ($log(L_{bol}/ergs^{-1})\simeq$47-48) broad-line quasars at $z\simeq$1.4-2.7. Sixteen of the 28 quasars show evidence for star formation with an average extinction-corrected star formation rate (SFR) of 320$\pm$70M$_\odot$yr$^{-1}$. A stacked spectrum of the detections shows weak [NII], consistent with star formation as the origin of the narrow H$\alpha$ emission. The star-forming regions are spatially unresolved in 11 of the 16 detections and constrained to lie within $\sim$6kpc of the quasar emission. In the five resolved detections we find the star-forming regions are extended on scales of $\sim$8kpc around the quasar emission. The prevalence of high SFRs is consistent with the identification of the heavily reddened quasar population as representing a transitional phase from apparent `starburst galaxies' to optically-luminous quasars. Upper limits are determined for 10 quasars in which star formation is undetected. In two of the quasars the SFR is constrained to be relatively modest, $<$50M$_\odot$yr$^{-1}$, but significantly higher levels of star formation could be present in the other eight quasars. The combination of the 16 strong star formation detections and the eight high SFR limits means that high levels of star formation may be present in the majority of the sample. Higher spatial resolution data, of multiple emission lines, will allow us to better understand the interplay between star formation and Active Galactic Nucleus (AGN) activity in these transitioning quasars.
This article is based on an invited talk given by V. P. Kulkarni at the 8th Cosmic Dust meeting. Dust has a profound effect on the physics and chemistry of the interstellar gas in galaxies and on the appearance of galaxies. Understanding the cosmic evolution of dust with time is therefore crucial for understanding the evolution of galaxies. Despite the importance of interstellar dust, very little is known about its nature and composition in distant galaxies. We summarize the results of our ongoing programs using observations of distant quasars to obtain better constraints on dust grains in foreground galaxies that happen to lie along the quasar sightlines. These observations consist of a combination of mid-infrared data obtained with the Spitzer Space Telescope and optical/UV data obtained with ground-based telescopes and/or the Hubble Space Telescope. The mid-IR data target the 10 $\mu$m and 18 $\mu$m silicate absorption features, while the optical/UV data allow determinations of element depletions, extinction curves, 2175 {\AA} bumps, etc. Measurements of such properties in absorption-selected galaxies with redshifts ranging from $z\sim0$ to $z>2$ provide constraints on the evolution of interstellar dust over the past $> 10$ Gyr. The optical depth of the 10 $\mu$m silicate absorption feature ($\tau_{10}$) in these galaxies is correlated with the amount of reddening along the sightline. But there are indications [e.g., based on the $\tau_{10}$ /$E(B-V)$ ratio and possible grain crystallinity] that the dust in these distant galaxies differs in structure and composition from the dust in the Milky Way and the Magellanic Clouds. We briefly discuss the implications of these results for the evolution of galaxies and their star formation history.
In this letter, we show that the newly detected H.E.S.S. gamma-ray diffuse emission from the Galactic center below 0.45 deg can be accounted for by inverse Compton emission from millisecond pulsars and heavy (~ 100 TeV) dark matter annihilating to electrons or muons with a thermal or sub-thermal cross-section, provided that the dark matter density profile features a supermassive black hole-induced spike on sub-pc scales. We discuss the impact of the interstellar radiation field, magnetic field and diffusion set-up on the spectral and spatial morphology of the resulting emission. For well-motivated parameters, we show that the DM-induced emission reproduces the spatial morphology of the H.E.S.S. signal above ~ 10 TeV, while we obtain a more extended component from pulsars at lower energies, which could be used as a prediction for future H.E.S.S. observations.
The HST Frontier Fields cluster MACS J1149.6+2223 is one of the most complex merging clusters, believed to consist of four dark matter halos. We present results from deep (365 ks) Chandra observations of the cluster, which reveal the most distant cold front (z=0.544) discovered to date. In the cluster outskirts, we also detect hints of a surface brightness edge that could be the bow shock preceding the cold front. The substructure analysis of the cluster identified several components with large relative radial velocities, thus indicating that at least some collisions occur almost along the line of sight. The inclination of the mergers with respect to the plane of the sky poses significant observational challenges at X-ray wavelengths. MACS J1149.6+2223 possibly hosts a steep-spectrum radio halo. If the steepness of the radio halo is confirmed, then the radio spectrum, combined with the relatively regular ICM morphology, could indicate that MACS J1149.6+2223 is an old merging cluster.
Cosmic rays (CRs) in starburst galaxies produce high energy gamma-rays by colliding with the dense interstellar medium. Arp 220 is the nearest ultra luminous infrared galaxy (ULIRG) that has star-formation at extreme levels, so it has long been predicted to emit high-energy gamma-rays. However, no evidence of gamma-ray emission was found despite intense efforts of search. Here we report the discovery of high-energy gamma-ray emission above 200 MeV from Arp 220 at a confidence level of $\sim 6.3 \sigma $ using 7.5 years of \textsl {Fermi} Large Area Telescope observation. The gamma-ray emission shows no significant variability over the observation period and it obeys the quasi-linear scaling relation between the gamma-ray luminosity and total infrared luminosity for star-forming galaxies, suggesting that these gamma-rays arise from CR interactions. As the high density gas makes Arp 220 an ideal CR calorimeter, the gamma-ray luminosity can be used to measure the efficiency of powering CRs by supernova remnants given a known supernova rate in Arp 220. We find that this efficiency is about $4.2\pm2.6\%$ for CRs above 1 GeV.
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Pulsar timing arrays are now setting increasingly tight limits on the gravitational wave background from binary supermassive black holes. But as upper limits grow more constraining, what can be implied about galaxy evolution? We investigate which astrophysical parameters have the largest impact on strain spectrum predictions and provide a simple framework to directly translate between measured values for the parameters of galaxy evolution and PTA limits on the gravitational wave background of binary supermassive black holes. We find that the most influential observable is the relation between a host galaxy's central bulge and its central black hole, $\mbox{$M_{\bullet}$-$M_{\rm bulge}$}$, which has the largest effect on the mean value of the characteristic strain amplitude. However, the variance of each prediction is dominated by uncertainties in the galaxy stellar mass function. Using this framework with the best published PTA limit, we can set limits on the shape and scatter of the $\mbox{$M_{\bullet}$-$M_{\rm bulge}$}$ relation. We find our limits to be in contention with strain predictions using two leading measurements of this relation. We investigate several possible reasons for this disagreement. If we take the $\mbox{$M_{\bullet}$-$M_{\rm bulge}$}$ relations to be correct within a simple power-law model for the gravitational wave background, then the inconsistency is reconcilable by allowing for an additional `stalling' time between a galaxy merger and evolution of a binary supermassive black hole to sub-parsec scales, with lower limits on this timescale of $\sim 1-2$ Gyr.
We present 947 radial velocities of RR Lyrae variable stars in four fields located toward the Galactic bulge, observed within the data from the ongoing Bulge RR Lyrae Radial Velocity Assay (BRAVA-RR). We show that these RR Lyrae stars exhibit hot kinematics and null or negligible rotation and are therefore members of a separate population from the bar/pseudobulge that currently dominates the mass and luminosity of the inner Galaxy. Our RR Lyrae stars predate these structures, and have metallicities, kinematics, and spatial distribution that are consistent with a "classical" bulge, although we cannot yet completely rule out the possibility that they are the metal-poor tail of a more metal rich ([Fe/H] ~ -1 dex) halo-bulge population. The complete catalog of radial velocities for the BRAVA-RR stars is also published electronically.
We apply a friends-of-friends algorithm to an enhanced SDSS DR12 spectroscopic catalog including redshift from literature to construct a catalog of $1588~N\ge3$ compact groups of galaxies containing 5179 member galaxies and covering the redshift range $0.01 < z < 0.19$. This catalog contains 18 times as many systems and reaches 3 times the depth of similar catalog of Barton et al. (1996). We construct catalogs from both magnitude-limited and volume-limited galaxy samples. Like Barton et al. (1996) we omit the frequently applied isolation criterion in the compact group selection algorithm. Thus the groups selected by fixed projected spatial and rest frame line-of-sight velocity separation produce a catalog of groups with a redshift independent median size. In contrast with previous catalogs, the enhanced SDSS DR12 catalog (including galaxies with $r < 14.5$) includes many systems with $z\leq 0.05$. The volume-limited samples are unique to this study. The compact group candidates in these samples have a median stellar mass independent of redshift. Groups with velocity dispersion $\leq 100$ km s$^{-1}$ show abundant evidence for ongoing dynamical interactions among the members. The number density of the volume-limited catalogs agrees with previous catalogs at the lowest redshifts but decreases as the redshift increases. The SDSS fiber placement constraints limit the catalog completeness. In spite of this issue the volume-limited catalogs provide a promising basis for detailed spatially resolved probes of the impact of galaxy-galaxy interactions within similar dense systems over a broad redshift range.
We explore the gas ionization and kinematics, as well as the optical--IR spectral energy distributions for UGC 11185, a nearby pair of merging galaxies hosting obscured active galactic nuclei (AGNs), also known as SDSS J181611.72+423941.6 and J181609.37+423923.0 (J1816NE and J1816SW, $z \approx 0.04$). Due to the wide separation between these interacting galaxies ($\sim 23$ kpc), observations of these objects provide a rare glimpse of the concurrent growth of supermassive black holes at an early merger stage. We use BPT line diagnostics to show that the full extent of the narrow line emission in both galaxies is photoionized by an AGN and confirm the existence of a 10-kpc-scale ionization cone in J1816NE, while in J1816SW the AGN narrow-line region is much more compact (1--2 kpc) and relatively undisturbed. Our observations also reveal the presence of ionized gas that nearly spans the entire distance between the galaxies which is likely in a merger-induced tidal stream. In addition, we carry out a spectral analysis of the X-ray emission using data from {\em XMM-Newton}. These galaxies represent a useful pair to explore how the [\ion{O}{3}] luminosity of an AGN is dependent on the size of the region used to explore the extended emission. Given the growing evidence for AGN "flickering" over short timescales, we speculate that the appearances and impact of these AGNs may change multiple times over the course of the galaxy merger, which is especially important given that these objects are likely the progenitors of the types of systems commonly classified as "dual AGNs."
We compare the Baryonic Tully-Fisher relation (BTFR) of simulations and observations of galaxies ranging from dwarfs to spirals, using various measures of rotational velocity Vrot. We explore the BTFR when measuring Vrot at the flat part of the rotation curve, Vflat, at the extent of HI gas, Vlast, and using 20% (W20) and 50% (W50) of the width of HI line profiles. We also compare with the maximum circular velocity of the parent halo, Vmax, within dark matter only simulations. The different BTFRs increasingly diverge as galaxy mass decreases. Using Vlast one obtains a power law over four orders of magnitude in baryonic mass, with slope similar to the observed BTFR. Measuring Vflat gives similar results as Vlast when galaxies with rising rotation curves are excluded. However, higher rotation velocities would be found for low mass galaxies if the cold gas extended far enough for Vrot to reach a maximum. W20 gives a similar slope as Vlast but with slightly lower values of Vrot for low mass galaxies, although this may depend on the extent of the gas in your galaxy sample. W50 bends away from these other relations toward low velocities at low masses. By contrast, Vmax bends toward high velocities for low mass galaxies, as cold gas does not extend out to the radius at which halos reach Vmax. Our study highlights the need for careful comparisons between observations and models: one needs to be consistent about the particular method of measuring Vrot, and precise about the radius at which velocities are measured.
The stellar debris structures that have been discovered around the Milky Way and other galaxies are thought to be formed from the disruption of satellite stellar systems --- dwarf galaxies or globular clusters --- by galactic tidal fields. The total stellar mass in these structures is typically tiny compared to the galaxy around which they are found, and it is hence easy to dismiss them as inconsequential. However, they are remarkably useful as probes of a galaxy's history (as described in this chapter) and mass distribution (covered in a companion chapter in this volume). This power is actually a consequence of their apparent insignificance: their low contribution to the overall mass makes the physics that describes them both elegant and simple and this means that their observed properties are relatively easy to understand and interpret.
Tidal debris streams from galaxy satellites can provide insight into the dark matter distribution in halos. This is because we have more information about stars in a debris structure than about a purely random population of stars: we know that in the past they were all bound to the same dwarf galaxy; and we know that they form a dynamically cold population moving on similar orbits. They also probe a different region of the matter distribution in a galaxy than many other methods of mass determination, as their orbits take them far beyond the typical extent of those for the bulk of stars. Although conclusive results from this information have yet to be obtained, significant progress has been made in developing the methodologies for determining both the global mass distribution of the Milky Way's dark matter halo and the amount of dark matter substructure within it. Methods for measuring the halo shape are divided into "predictive methods," which predict the tidal debris properties from the progenitor satellite's mass and orbit, given an assumed parent galaxy mass distribution; and "fundamental methods," which exploit properties fundamental to the nature of tidal debris as global potential constraints. Methods for quantifying the prevalence of dark matter subhalos within halos through the analysis of the gaps left in tidal streams after these substructures pass through them are reviewed.
A nearby source of Lyman-Werner (LW) photons is thought to be a central component in dissociating H$_2$ and allowing for the formation of a direct collapse black hole seed. Nearby sources are also expected to produce copious amounts of hydrogen ionising photons and X-ray photons. We study here the feedback effects of the X-ray photons by including a spectrum due to high-mass X-ray binaries on top of a galaxy with a stellar spectrum. We explicitly trace photon packages emerging from the nearby source and track the radiative and chemical effects of the multi-frequency source $(E_{\rm photon} = \rm{0.76\ eV \rightarrow 7500\ eV}$). We find that X-rays have a strongly negative feedback effect, compared to a stellar only source, when the radiative source is placed at a separation greater than $\gtrsim 1 \ \rm kpc$. The X-rays heat the low and medium density gas in the envelope surrounding the collapsing halo suppressing the mass inflow. The result is a smaller enclosed mass compared to the stellar only case. However, for separations of $\lesssim 1 \ \rm kpc$, the feedback effects of the X-rays becomes somewhat neutral. The enhanced LW intensity at close separations dissociates more H$_2$ and this gas is heated due to stellar photons alone, the addition of X-rays is then not significant. This distance dependence of X-ray feedback suggests that a Goldilocks zone exists close to a forming galaxy where X-ray photons have a much smaller negative feedback effect and ideal conditions exist for creating massive black hole seeds.
We report on the detection of Lyman continuum radiation in two nearby starburst galaxies. Tol 0440-381, Tol 1247-232 and Mrk 54 were observed with the Cosmic Origins Spectrograph onboard the Hubble Space Telescopes. The three galaxies have radial velocities of ~13,000 km/s, permitting a ~35 A window on the restframe Lyman continuum shortward of the Milky Way Lyman edge at 912 A. The chosen instrument configuration using the G140L grating covers the spectral range from 912 to 2,000 {\AA}. We developed a dedicated background subtraction method to account for temporal and spatial background variations of the detector, which is crucial at the low flux levels around 912 A. This modified pipeline allowed us to significantly improve the statistical and systematic detector noise and will be made available to the community. We detect Lyman continuum in all three galaxies. However, we conservatively interpret the emission in Tol 0440-381 as an upper limit due to possible contamination by geocoronal Lyman series lines. We determined the current star-formation properties from the far-ultraviolet continuum and spectral lines and used synthesis models to predict the Lyman continuum radiation emitted by the current population of hot stars. We discuss the various model uncertainties such as, among others, atmospheres and evolution models. Lyman continuum escape fractions were derived from a comparison between the observed and predicted Lyman continuum fluxes. Tol 1247-232, Mrk 54 and Tol 0440-381 have absolute escape fractions of (4.5 +/- 1.2)%, (2.5 +/- 0.72)% and <(7.1 +/- 1.1)%, respectively.
We present results for an up-to-date uncatalogued star cluster projected towards the Eastern side of the Large Magellanic Cloud (LMC) outer disc. The new object was discovered from a search of loose star cluster in the Magellanic Clouds' (MCs) outskirts using kernel density estimators on Washington CT1 deep images. Contrarily to what would be commonly expected, the star cluster resulted to be a young object (log(t /yr) = 8.45) with a slightly subsolar metal content (Z = 0.013) and a total mass of 650Mo. Its core, half-mass and tidal radii also are within the frequent values of LMC star clusters. However, the new star cluster is placed at the Small Magellanic Cloud distance and at 11.3 kpc from the LMC centre. We speculate with the possibility that it was born in the inner body of the LMC and soon after expeled into the intergalactic space during the recent Milky Way/MCs interaction. Nevertheless, radial velocity and chemical abundance measurements are needed to further understand its origin, as well as extensive search for loose star clusters in order to constrain the effectiveness of star cluster scattering during galaxy interactions.
We investigated the optical/ultraviolet (UV) color variations for a sample of 2169 quasars based on multi-epoch spectroscopy in the Sloan Digital Sky Survey (SDSS) data release seven (DR7) and data release nine (DR9). To correct the systematic difference between DR7 and DR9 due to the different instrumental setup, we produced a correction spectrum by using a sample of F-stars observed both in DR7 and DR9. The correction spectrum was then applied to quasars when comparing the spectra of DR7 with DR9. In each object, the color variation was explored by comparing the spectral index of the continuum power-law fit on the brightest spectrum with the faintest one, and also by the shape of their difference spectrum. In 1876 quasars with consistent color variations from two methods, we found that most sources (1755, $\sim 94\%$) show bluer-when-brighter (BWB) trend, and the redder-when-brighter (RWB) trend is only detected in 121 objects ($\sim 6\%$). The common BWB trend is supported by the bluer composite spectrum constructed from bright spectra than that from faint spectra, and also by the blue composite difference spectrum. The correction spectrum is proved to be highly reliable by comparing the composite spectrum from corrected DR9 and original DR7 spectra. Assuming that the optical/UV variability is triggered by fluctuations, RWB trend can likely be explained if the fluctuations occur firstly at outer disk region, and the inner disk region has not fully responded yet when the fluctuation being propagated inward. In contrast, the common BWB trend implies that the fluctuations are likely more often happening firstly in inner disk region.
The SHELS (Smithsonian Hectospec Lensing Survey) is a complete redshift survey covering two well-separated fields (F1 and F2) of the Deep Lens Survey. Both fields are more than 94% complete to a Galactic extinction corrected R0 = 20.2. Here we describe the redshift survey of the F1 field centered at R.A. = 00h53m25.3s and Decl = 12d33m55s; like F2, the F1 field covers 4 sq deg. The redshift survey of the F1 field includes 9426 new galaxy redshifts measured with Hectospec on the MMT (published here). As a guide to future uses of the combined survey we compare the mass metallicity relation and the distributions of D4000 as a function of stellar mass and redshift for the two fields. The mass-metallicity relations differ by an insignificant 1.6 sigma. For galaxies in the stellar mass range 1.e10 to 1.e11 MSun, the increase in the star-forming fraction with redshift is remarkably similar in the two fields. The seemingly surprising 31-38% difference in the overall galaxy counts in F1 and F2 is probably consistent with the expected cosmic variance given the subtleties of the relative systematics in the two surveys. We also review the Deep Lens Survey cluster detections in the two fields: poorer photometric data for F1 precluded secure detection of the single massive cluster at z = 0.35 that we find in SHELS. Taken together the two fields include 16,055 redshifts for galaxies with R0 <= 20.2 and 20,754 redshifts for galaxies with R <= 20.6. These dense surveys in two well-separated fields provide a basis for future investigations of galaxy properties and large-scale structure.
We present an imaging analysis of four low mass stellar clusters (< 5000 Mo) in the outer regions of the LMC in order to shed light on the extended main sequence turn-off (eMSTO) phenomenon observed in high mass clusters. The four clusters have ages between 1-2 Gyr and two of them appear to host eMTSOs. The discovery of eMSTOs in such low mass clusters - > 5 times less massive than the eMSTO clusters previously studied - suggests that mass is not the controlling factor in whether clusters host eMSTOs. Additionally, the narrow extent of the eMSTO in the two older (~ 2 Gyr) clusters is in agreement with predictions of the stellar rotation scenario, as lower mass stars are expected to be magnetically braked, meaning that their CMDs should be better reproduced by canonical simple stellar populations. We also performed a structural analysis on all the clusters and found that a large core radius is not a requisite for a cluster to exhibit an eMSTO.
Results of the application of pattern recognition techniques to the problem of identifying Giant Radio Sources (GRS) from the data in the NVSS catalog are presented and issues affecting the process are explored. Decision-tree pattern recognition software was applied to training set source pairs developed from known NVSS large angular size radio galaxies. The full training set consisted of 51,195 source pairs, 48 of which were known GRS for which each lobe was primarily represented by a single catalog component. The source pairs had a maximum separation of 20 arc minutes and a minimum component area of 1.87 square arc minutes at the 1.4 mJy level. The importance of comparing resulting probability distributions of the training and application sets for cases of unknown class ratio is demonstrated. The probability of correctly ranking a randomly selected (GRS, non-GRS) pair from the best of the tested classifiers was determined to be 97.8 +/- 1.5%. The best classifiers were applied to the over 870,000 candidate pairs from the entire catalog. Images of higher ranked sources were visually screened and a table of over sixteen hundred candidates, including morphological annotation, is presented. These systems include doubles and triples, Wide-Angle Tail (WAT) and Narrow-Angle Tail (NAT), S- or Z-shaped systems, and core-jets and resolved cores. While some resolved lobe systems are recovered with this technique, generally it is expected that such systems would require a different approach.
We present the first results from an extended survey of the Andromeda galaxy (M31) using 41.1 hours of observations by Spitzer-IRAC at 3.6 and 4.5 \mu m. This survey extends previous observations to the outer disc and halo, covering total lengths of 4$.\!\!^\circ$4 and 6$.\!\!^\circ$6 along the minor and major axes, respectively. We have produced surface brightness profiles by combining the integrated light from background-corrected maps with stellar counts from a new catalogue of point sources. Using auxiliary catalogues we have carried out a statistical analysis in colour-magnitude space to discriminate M31 objects from foreground Milky Way stars and background galaxies. The catalogue includes 426,529 sources, of which 66 per cent have been assigned probability values to identify M31 objects with magnitude depths of [3.6]$\,=\,$19.0$\,\pm\,$0.2, [4.5]$\,=\,$18.7$\,\pm\,$0.2. We discuss applications of our data for constraining the stellar mass and characterising point sources in the outer radii.
The recent discovery of the gravitational wave source GW150914 has revealed a coalescing binary black hole (BBH) with masses of $\sim 30~\odot$. A possible origin of such a massive binary is Population III (PopIII) stars. PopIII stars are efficient producers of BBHs and of a gravitational wave background (GWB) in the $10-100$ Hz band, and also of ionizing radiation in the early Universe. We show that PopIII stars that are consistent with the recent Planck measurement of a low electron scattering optical depth $\tau_{\rm e}=0.066\pm0.016$ could still produce a GWB dominating other binary populations. Moreover, the spectral index of the background from PopIII BBHs becomes flatter at $f\gtrsim 20$ Hz than the value ${\rm d}\ln \Omega_{\rm gw}/{\rm d}\ln f\approx 2/3$ generically produced by lower-redshift and less-massive BBHs. A detection of this unique flattening by the future O5 LIGO/Virgo would be a smoking gun of a high-chirp mass, high-redshift BBH population, as expected from PopIII stars. It would also constrain the PopIII initial mass function and star formation rate and the cosmic reionization history.
Fermi-LAT observations of the Galactic Center (GC) have revealed a spherically- symmetric excess of GeV gamma rays extending to at least 10 deg from the dynamical center of the Galaxy. A critical uncertainty in extracting the intensity, spectrum, and morphology of this excess concerns the accuracy of astrophysical diffuse gamma-ray emission models near the GC. Recently, it has been noted that many diffuse emission models utilize a cosmic-ray injection rate far below that predicted based on the observed star formation rate in the Central Molecular Zone. In this study, we add a cosmic-ray injection component which non-linearly traces the Galactic H2 density determined in three-dimensions, and find that the associated gamma-ray emission is degenerate with many properties of the GC gamma-ray excess. In models that utilize a large sideband (40x40 deg surrounding the GC) to normalize the best-fitting diffuse emission models, the intensity of the GC excess decreases by a factor of 2, and the morphology of the excess becomes less peaked and less spherically symmetric. In models which utilize a smaller region of interest (15x15 deg) the addition of an excess template instead suppresses the intensity of the best-fit astrophysical diffuse emission, and the GC excess is rather resilient to changes in the details of the astrophysical diffuse modeling. In both analyses, the addition of a GC excess template still provides a statistically significant improvement to the overall fit to the gamma-ray data. We also implement advective winds at the GC, and find that the Fermi-LAT data strongly prefer outflows of order several hundred km/s, whose role is to efficiently advect low-energy cosmic rays from the Galactic center. Finally, we perform numerous tests of our models, and conclude that they significantly improve our understanding of multi-wavelength non-thermal emission from the GC.
The sources that drove cosmological reionization left clues regarding their identity in the slope and inhomogeneity of the ultraviolet ionizing background (UVB): Bright quasars (QSOs) generate a hard UVB with predominantly large-scale fluctuations while Population II stars generate a softer one with smaller-scale fluctuations. Metal absorbers probe the UVB's slope because different ions are sensitive to different energies. Likewise, they probe spatial fluctuations because they originate in regions where a galaxy-driven UVB is harder and more intense. We take a first step towards studying the reionization-epoch UVB's slope and inhomogeneity by comparing observations of 12 metal absorbers at $z\sim6$ versus predictions from a cosmological hydrodynamic simulation using three different UVBs: a soft, spatially-inhomogeneous "galaxies+QSOs" UVB; a homogeneous "galaxies+QSOs" UVB (Haardt & Madau 2012); and a QSOs-only model. All UVBs reproduce the observed column density distributions of CII, SiIV, and CIV reasonably well although high-column, high-ionization absorbers are underproduced, reflecting numerical limitations. With upper limits treated as detections, only a soft, fluctuating UVB reproduces both the observed SiIV/CIV and CII/CIV distributions. The QSOs-only UVB overpredicts both CIV/CII and CIV/SiIV, indicating that it is too hard. The Haardt & Madau (2012) UVB underpredicts CIV/SiIV, suggesting that it lacks amplifications near galaxies. Hence current observations prefer a soft, fluctuating UVB as expected from a predominantly Population II background although they cannot rule out a harder one. Future observations probing a factor of two deeper in metal column density will distinguish between the soft, fluctuating and QSOs-only UVBs.
We present Spitzer Space Telescope archival mid-infrared (mid-IR) spectroscopy of a sample of eleven planetary nebulae (PNe). The observations, acquired with the Spitzer Infrared Spectrograph (IRS), cover the spectral range 5.2-14.5 {\mu}m that includes the H2 0-0 S(2) to S(7) rotational emission lines. This wavelength coverage has allowed us to derive the Boltzmann distribution and calculate the H2 rotational excitation temperature (Tex). The derived excitation temperatures have consistent values ~900+/-70 K for different sources despite their different structural components. We also report the detection of mid-IR ionic lines of [Ar III], [S IV], and [Ne II] in most objects, and polycyclic aromatic hydrocarbon (PAH) features in a few cases. The decline of the [Ar III]/[Ne II] line ratio with the stellar effective temperature can be explained either by a true neon enrichment or by high density circumstellar regions of PNe that presumably descend from higher mass progenitor stars.
Planetary nebulae (PNe) are expected to have a ~10$^{5}$ K interface layer between the $\geq$10$^{6}$ K inner hot bubble and the ~10$^{4}$ K optical nebular shell. The PN structure and evolution, and the X-ray emission depend critically on the efficiency of mixing of material at this interface layer. However, neither its location nor its spatial extent has ever been determined so far. Using high-spatial resolution HST STIS spectroscopic observations of the N V 1239,1243 lines in the Cat's Eye Nebula (NGC 6543), we have detected this interface layer and determined its location, extent, and physical properties for the first time in a PN. We confirm that this interface layer, as revealed by the spatial distribution of the N V 1239 line emission, is located between the hot bubble and the optical nebular shell. We estimate a thickness of 1.5$\times$10$^{16}$ cm and an electron density of ~200 cm$^{-3}$ for the mixing layer. With a thermal pressure of ~2$\times$10$^{-8}$ dyn cm$^{-2}$, the mixing layer is in pressure equilibrium with the hot bubble and ionized nebular rim of NGC 6543.
To probe the circumstellar environment of IRAS 13481-6124, a 20 M_sun high-mass young stellar object (HMYSO) with a parsec-scale jet and accretion disc, we investigate the origin of its Br\gamma-emission line through NIR interferometry. We present the first AMBER/VLTI observations of the Br\gamma-emitting region in an HMYSO at R~1500. Our AMBER/VLTI observations reveal a spatially and spectrally resolved Br\gamma-line in emission with a strong P Cygni profile, indicating outflowing matter with a terminal velocity of ~500 km/s. Visibilities, differential phases, and closure phases are detected in our observations within the spectral line and in the adjacent continuum. Both total visibilities (continuum plus line emitting region) and pure-line visibilities indicate that the Br\gamma-emitting region is more compact (2-4 mas in diameter or ~6-13 au at 3.2 kpc) than the continuum-emitting region (~5.4 mas or ~17 au). The absorption feature is also spatially resolved at the longest baselines (81 and 85 m) and has a visibility that is slightly smaller than the continuum-emitting region. The differential phases at the four longest baselines display an \u2018S\u2019-shaped structure across the line, peaking in the blue- and red-shifted high-velocity components. The calibrated photocentre shifts are aligned with the known jet axis, i.e they are probably tracing an ionised jet. The high-velocity components (v_r~100-500 km/s) are located far from the source, whereas the low-velocity components (0-100 km/s) are observed to be closer, indicating a strong acceleration of the gas flow in the inner 10 au. Finally, a non-zero closure phase along the continuum is detected. By comparing our observations with the synthetic images of the continuum around 2.16 um, we confirm that this feature originates from the asymmetric brightness distribution of the continuum owing to the inclination of the inner disc.
The detection and study of extrasolar planets is an exciting and thriving field in modern astrophysics, and an increasingly popular topic in introductory astronomy courses. One detection method relies on searching for stars whose light has been gravitationally microlensed by an extrasolar planet. In order to facilitate instructors' abilities to bring this interesting mix of general relativity and extrasolar planet detection into the introductory astronomy classroom, we have developed a new Lecture-Tutorial, "Detecting Exoplanets with Gravitational Microlensing." In this paper, we describe how this new Lecture-Tutorial's representations of astrophysical phenomena, which we selected and created based on theoretically motivated considerations of their pedagogical affordances, are used to help introductory astronomy students develop more expert-like reasoning abilities.
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We carry out a joint spatial-kinematical-metallicity analysis of globular clusters (GCs) around the Andromeda Galaxy (M31), using a homogeneous, high-quality spectroscopic dataset. In particular, we remove the contaminating young clusters that have plagued many previous analyses. We find that the clusters can be divided into three major metallicity groups based on their radial distributions: (1) an inner metal-rich group ([Fe/H] > -0.4), (2) a group with intermediate metallicity (with median [Fe/H]=-1), (3) and a metal-poor group, with [Fe/H] < -1.5. The metal-rich group has kinematics and spatial properties like the disk of M31, while the two more metal-poor groups show mild prograde rotation overall, with larger dispersions - in contrast to previous claims of stronger rotation. The metal-poor GCs are the least concentrated group; such clusters occur five times less frequently in the central bulge than do clusters of higher metallicity. Despite some well-known differences between the M31 and Milky Way GC systems, our revised analysis points to remarkable similarities in their chemodynamical properties, which could help elucidate the different formation stages of galaxies and their GCs. In particular, the M31 results motivate further exploration of a metal-rich GC formation mode in situ, within high-redshift, clumpy galactic disks.
The typical optical-UV continuum slopes observed in many type 1 active galactic nuclei (AGN) are redder than expected from thin accretion disk models. A possible resolution to this conundrum is that many AGN are reddened by dust along the line of sight. To explore this possibility, we stack 5000 SDSS AGN with luminosity L ~ 10^45 erg/s and redshift z ~ 0.4 in bins of optical continuum slope alpha_opt and width of the broad Hbeta emission line. We measure the equivalent width (EW) of the NaID absorption feature in each stacked spectrum. We find a linear relation between alpha_opt and EW(NaID), such that EW(NaID) increases as alpha_opt becomes redder. In the bin with the smallest Hbeta width, objects with the bluest slopes that are similar to accretion disk predictions are found to have EW(NaID) = 0, supporting the line-of-sight dust hypothesis. This conclusion is also supported by the dependence of the Halpha/Hbeta line ratio on alpha_opt. The implied relationship between continuum slope and dust reddening is given by E(B-V) ~ 0.2(-0.1 - alpha_opt), and the implied reddening of a typical type 1 AGN with alpha_opt = -0.5 is E(B-V) ~ 0.08 mag. The relation between E(B-V) and NaI column is similar to the relation in the Milky-Way found in previous studies. Combining this fact with photoionization calculations, we argue that the line-of-sight dusty gas is the interstellar medium of the host galaxy, and that the sodium absorption arises in regions shielded from the AGN radiation, along the line of sight to the stars.
A large fraction of the baryonic matter in the Universe is located in filaments in the intergalactic medium. However, the low surface brightness of these filaments has not yet allowed their direct detection except in very special regions in the circum-galactic medium (CGM). Here we simulate the intensity and spatial fluctuations in Lyman Alpha ${\rm (Ly\alpha)}$ emission from filaments in the intergalactic medium (IGM) and discuss the prospects for the next generation of space based instruments to detect the low surface brightness universe at UV wavelengths. Starting with a high resolution N-body simulation we obtain the dark matter density fluctuations and associate baryons with the dark matter particles assuming that they follow the same spatial distribution. The IGM thermal and ionization state is set by a model of the UV background and by the relevant cooling processes for a hydrogen and helium gas. The ${\rm Ly\alpha}$ emissivity is then estimated, taking into account recombination and collisional excitation processes. We find that the detection of these filaments through their ${\rm Ly\alpha}$ emission is well in the reach of the next generation of UV space based instruments and so it should be achieved in the next decade. The density field is populated with halos and galaxies and their ${\rm Ly\alpha}$ emission is estimated. Galaxies are treated as foregrounds and so we discuss methods to reduce their contamination from observational maps. Finally, we estimate the UV continuum background as a function of the redshift of the ${\rm Ly\alpha}$ emission line and discuss how this continuum can affect observations.
The blue compact dwarf galaxy NGC 5253 hosts a very young starburst containing twin nuclear star clusters, separated by a projected distance of 5 pc. One cluster (#5) coincides with the peak of the H-alpha emission and the other (#11) with a massive ultracompact H II region. A recent analysis of these clusters shows that they have a photometric age of 1+/-1 Myr, in apparent contradiction with the age of 3-5 Myr inferred from the presence of Wolf-Rayet features in the cluster #5 spectrum. We examine Hubble Space Telescope ultraviolet and Very Large Telescope optical spectroscopy of #5 and show that the stellar features arise from very massive stars (VMS), with masses greater than 100 Msun, at an age of 1-2 Myr. We further show that the very high ionizing flux from the nuclear clusters can only be explained if VMS are present. We investigate the origin of the observed nitrogen enrichment in the circum-cluster ionized gas and find that the excess N can be produced by massive rotating stars within the first 1 Myr. We find similarities between the NGC 5253 cluster spectrum and those of metal poor, high redshift galaxies. We discuss the presence of VMS in young, star-forming galaxies at high redshift; these should be detected in rest frame UV spectra to be obtained with the James Webb Space Telescope. We emphasize that population synthesis models with upper mass cut-offs greater than 100 Msun are crucial for future studies of young massive star clusters at all redshifts.
Understanding the processes that could lead to enrichment of molecules in $^{15}$N atoms is of particular interest in order to shed light on the relatively large variations observed in the $^{14}$N/$^{15}$N ratio in various solar system environments. Currently, the sample of molecular clouds where $^{14}$N/$^{15}$N ratios have been measured is small and has to be enlarged in order to allow statistically significant studies. In particular, the N$_2$H$^+$ molecule currently shows the largest spread of $^{14}$N/$^{15}$N ratios in high-mass star forming regions. However, the $^{14}$N/$^{15}$N ratio in N$_2$H$^+$ was obtained in only two low-mass star forming regions (L1544 and B1b). The current work extends this sample to a third dark cloud. We targeted the 16293E prestellar core, where the N$^{15}$NH$^+$ $J$=1-0 line was detected. Using a model previously developed for the physical structure of the source, we solved the molecular excitation with a non-local radiative transfer code. For that purpose, we computed specific collisional rate coefficients for the N$^{15}$NH$^+$-H$_2$ collisional system. As a first step of the analysis, the N$_2$H$^+$ abundance profile was constrained by reproducing the N$_2$H$^+$ $J$=1-0 and 3-2 maps. A scaling factor was then applied to this profile to match the N$^{15}$NH$^+$ $J$=1-0 spectrum. We derive a column density ratio N$_2$H$^+$ / N$^{15}$NH$^+$ = $330^{+170}_{-100}$. The current estimate $\sim$330 agrees with the value typical of the elemental isotopic ratio in the local ISM. It is however lower than in some other cores, where values as high as 1300 have been reported.
The origin of the radio emission in radio-quiet quasars (RQQs) has been a matter of debate for a long time. It is not well understood whether the emission is caused by star formation in the host galaxy or by black hole activity of the active galactic nuclei (AGN). We shed some light on these questions using the Very Long Baseline Interferometry (VLBI) technique to search for RQQs in the field of the Cosmological Evolution Survey (COSMOS). The extensive multi-wavelength coverage of the field (from radio to X-rays) was used to classify RQQs, and the milli-arcsecond resolution of VLBI provides a direct way to identify AGNs. In a sample of 18 RQQs we detected 3 using the Very Long Baseline Array (VLBA) at 1.4 GHz. In this letter we report for the first time on a sample of RQQs with a measured lower limit on the fraction of radio emission coming from the AGN, thus demonstrating that the radio emission of at least some RQQs is dominated by an AGN.
The mechanism of radio emission in radio-quiet (RQ) active galactic nuclei (AGN) is still debated and might arise from the central AGN, from star formation activity in the host, or from either of these sources. A direct detection of compact and bright radio cores embedded in sources that are classified as RQ can unambiguously determine whether a central AGN significantly contributes to the radio emission. We search for compact, high-surface-brightness radio cores in RQ AGNs that are caused unambiguously by AGN activity. We used the Australian Long Baseline Array to search for compact radio cores in four RQ AGNs located in the Extended Chandra Deep Field South (ECDFS). We also targeted four radio-loud (RL) AGNs as a control sample. We detected compact and bright radio cores in two AGNs that are classified as RQ and in one that is classified as RL. Two RL AGNs were not imaged because the quality of the observations was too poor. We report on a first direct evidence of radio cores in RQ AGNs at cosmological redshifts. Our detections show that some of the sources that are classified as RQ contain an active AGN that can contribute significantly (about 50% or more) to the total radio emission.
We have obtained K-band spectra at R~5,000 and angular resolution 0.3" of a section of the Herbig-Haro 7 (HH7) bow shock, using the Near-Infrared Integral Field Spectrograph at Gemini North. Present in the portion of the data cube corresponding to the brightest part of the bow shock are emission lines of H2 with upper state energies ranging from ~6,000 K up to the dissociation energy of H2, ~50,000 K. Because of low signal-to-noise ratios, the highest excitation lines cannot be easily seen elsewhere in the observed region. However, excitation temperatures, measured throughout much of the observed region using lines from levels as high as 25,000 K, are a strong function of upper level energy, indicating that the very highest levels are populated throughout. The level populations in the brightest region are well fit by a two-temperature model, with 98.5% of the emitting gas at T=1800 K and 1.5% at T=5200 K. The bulk of the H2 line emission in HH7, from the 1,800 K gas, has previously been well modeled by a continuous shock, but the 5,200 K component is inconsistent with standalone standard continuous shock models. We discuss various possible origins for the hot component and suggest that this component is H2 newly reformed on dust grains and then ejected from them, presumably following dissociation of some of the H2 by the shock.
We present the first detailed chemical abundances for distant RR Lyrae stars members of the Virgo Stellar Stream (VSS), derived from X-Shooter medium-resolution spectra. Sixteen elements from carbon to barium have been measured in six VSS RR Lyrae stars, sampling all main nucleosynthetic channels. For the first time we will be able to compare in detail the chemical evolution of the VSS progenitor with those of Local Group dwarf spheroidal galaxies (LG dSph) as well as the one of the smooth halo.
This paper discusses a new method to generate self-coherent initial conditions for young substructured stellar cluster. The expansion of a uniform system allows stellar sub-structures (clumps) to grow from fragmentation modes by adiabatic cooling. We treat the system mass elements as stars, chosen according to a Salpeter mass function, and the time-evolution is performed with a collisional N-body integrator. This procedure allows to create a fully-coherent relation between the clumps' spatial distribution and the underlying velocity field. The cooling is driven by the gravitational field, as in a cosmological Hubble-Lema\^itre flow. The fragmented configuration has a `fractal'-like geometry but with a self-grown velocity field and mass profile. We compare the characteristics of the stellar population in clumps with that obtained from hydrodynamical simulations and find a remarkable correspondence between the two in terms of the stellar content and the degree of spatial mass-segregation. In the fragmented configuration, the IMF power index is ~0.3 lower in clumps in comparison to the field stellar population, in agreement with observations in the Milky Way. We follow in time the dynamical evolution of fully fragmented and sub-virial configurations, and find a soft collapse, leading rapidly to equilibrium (timescale of 1 Myr for a ~ 10^4 Msun system). The low-concentration equilibrium implies that the dynamical evolution including massive stars is less likely to induce direct collisions and the formation of exotic objects. Low-mass stars already ejected from merging clumps are depleted in the end-result stellar clusters, which harbour a top-heavy stellar mass function.
In this paper we provide formulae that can be used to determine the uncertainty contributed to a measurement by a $K$-correction and, thus, valuable information about which flux measurement will provide the most accurate $K$-corrected luminosity. All of this is done at the level of a Gaussian approximation of the statistics involved, that is, where the galaxies in question can be characterized by a mean spectral energy distribution (SED) and a covariance function (spectral 2-point function). This paper also includes approximations of the SED mean and covariance for galaxies, and the three common subclasses thereof, based on applying the templates from Assef et al. (2010) to the objects in zCOSMOS bright 10k (Lilly et al. 2009) and photometry of the same field from Capak et al. (2007), Sanders et al. (2007), and the AllWISE source catalog.
We study the radio properties of moderately obscured quasars over a range of redshifts to understand the role of radio activity in accretion using the Jansky Very Large Array (JVLA) at 6.0GHz and 1.4GHz. Our z~2.5 sample consists of optically-selected obscured quasar candidates, all of which are radio-quiet, with typical radio luminosities of $\nu L_{\nu}$[1.4 GHz] < $10^{40}$ erg s$^{-1}$. Only a single source is individually detected in our deep (rms~10 $\mu$Jy) exposures. This population would not be identified by radio-based selection methods used for distinguishing dusty star-forming galaxies and obscured active nuclei. In our pilot A-array study of z~0.5 radio-quiet quasars, we spatially resolve four of five objects on scales ~ 5 kpc and find they have steep spectral indices. Therefore, radio emission in these sources could be due to jet-driven or radiatively driven bubbles interacting with interstellar material on the scale of the host galaxy. Finally, we also study the population of ~ 200 faint (~40 $\mu$Jy - 40 mJy) radio sources observed over ~ 120 arcmin$^2$ of our data. 60% of these detections are matched in the SDSS and/or WISE and are, in roughly equal shares, active nuclei at a broad range of redshifts, passive galaxies with no other signs of nuclear activity and IR-bright but optically faint sources. Spectroscopically or photometrically confirmed star-forming galaxies constitute only a small minority of the matches. Such sensitive radio surveys allow us to address important questions of AGN evolution and evaluate the AGN contribution to the radio-quiet sky.
I review the literature covering the issue of interstellar extinction toward the Milky Way bulge, with emphasis placed on findings from planetary nebulae, RR Lyrae, and red clump stars. I also report on observations from HI gas and globular clusters. I show that there has been substantial progress in this field in recent decades, most particularly from red clump stars. The spatial coverage of extinction maps has increased by a factor $\sim 100 \times$ in the past twenty years, and the total-to-selective extinction ratios reported have shifted by $\sim$20-25\%, indicative of the improved accuracy and separately, of a steeper-than-standard extinction curve. Problems remain in modelling differential extinction, explaining anomalies involving the planetary nebulae, and understanding the difference between bulge extinction coefficients and "standard" literature values.
By incorporating our major recent discoveries with re-measured and verified contents of existing catalogues we provide, for the first time, an accessible, reliable, on-line SQL database for essential, up-to date information for all known Galactic PNe. We have attempted to: i) reliably remove PN mimics/false ID's that have biased previous studies and ii) provide accurate positions, sizes, morphologies, multi-wavelength imagery and spectroscopy. We also provide a link to CDS/Vizier for the archival history of each object and other valuable links to external data. With the HASH interface, users can sift, select, browse, collate, investigate, download and visualise the entire currently known Galactic PNe diversity. HASH provides the community with the most complete and reliable data with which to undertake new science.
We present a novel automatic adaptive aperture photometry algorithm for measuring the total magnitudes of merging galaxies with irregular shapes. First, we use a morphological pattern recognition routine for identifying the shape of an irregular source in a background-subtracted image. Then, we extend the shape of the source by using the Dilation image operation to obtain an aperture that is quasi-homomorphic to the shape of the irregular source. The magnitude measured from the homomorphic aperture would thus have minimal contamination from the nearby background. As a test of our algorithm, we applied our technique to the merging galaxies observed by the Sloan Digital Sky Survey (SDSS) and the Canada-France-Hawaii Telescope (CFHT). Our results suggest that the adaptive homomorphic aperture algorithm can be very useful for investigating extended sources with irregular shapes and sources in crowded regions.
We present the simulation framework CRPropa version 3 designed for efficient development of astrophysical predictions for ultra-high energy particles. Users can assemble modules of the most relevant propagation effects in galactic and extragalactic space, include their own physics modules with new features, and receive on output primary and secondary cosmic messengers including nuclei, neutrinos and photons. In extension to the propagation physics contained in a previous CRPropa version, the new version facilitates high-performance computing and comprises new physical features such as an interface for galactic propagation using lensing techniques, an improved photonuclear interaction calculation, and propagation in time dependent environments to take into account cosmic evolution effects in anisotropy studies and variable sources. First applications using highlighted features are presented as well.
Gamma-ray haloes can exist around galaxies due to the interaction of escaping galactic cosmic rays with the surrounding gas. We have searched for such a halo around the nearby giant spiral Andromeda galaxy M31 using almost 7 years of Fermi LAT data at energies above 300 MeV. The presence of a diffuse gamma-ray halo with total photon flux $2.6\pm 0.6\times 10^{-9}$ cm$^{-2}$~s$^{-1}$, corresponding to a luminosity (0.3-100 GeV) of $(3.2\pm 0.6)\times 10^{38}$ erg s$^{-1}$ (for a distance of 780~kpc) was found at a 5.3$\sigma$ confidence level. The halo form does not correspond to the extended baryonic HI disc of M31, as would be expected in hadronic production of gamma photons from cosmic ray interaction, nor it is spherically symmetric, as could be in the case of dark matter annihilation. The best-fit halo template corresponds to two 6-7.5 kpc bubbles symmetrically located perpendicular to the M31 galactic disc, similar to the 'Fermi bubbles' found around the Milky Way centre, which suggests the past activity of the central supermassive black hole or a star-formation burst in M31.
Understanding disk evolution and dissipation is essential for studies of planet formation. Transition disks, i.e., disks with large dust cavities and gaps, are promising candidates of active evolution. About two dozen SED-selected candidates have been confirmed to have dust cavities through millimeter interferometric imaging, but this sample is biased towards the brightest disks. The Spitzer surveys of nearby low-mass star forming regions have resulted in more than 4000 Young Stellar Objects (YSOs). Using color criteria we have selected a sample of ~150 candidates, and an additional 40 candidates and known transition disks from the literature. The Spitzer data were complemented by new observations at longer wavelengths, including new JCMT and APEX submillimeter photometry, and WISE and Herschel-PACS mid and far-infrared photometry. Furthermore, optical spectroscopy was obtained and stellar types were derived for 85% of the sample, including information from the literature. The SEDs were fit to a grid of RADMC-3D disk models with a limited number of parameters: disk mass, inner disk mass, scale height and flaring, and disk cavity radius, where the latter is the main parameter of interest. A large fraction of the targets possibly have dust cavities based on the SED. The derived cavity sizes are consistent with imaging/modeling results in the literature, where available. Trends are found with Ldisk/Lstar and stellar mass and a possible connection with exoplanet orbital radii. A comparison with a previous study where color observables are used (Cieza et al. 2010) reveals large overlap between their category of planet-forming disks and our transition disks with cavities. A large number of the new transition disk candidates are suitable for follow-up observations with ALMA.
Cold Dark Matter (CDM) models struggle to match the observations at galactic scales. The tension can be reduced either by dramatic baryonic feedback effects or by modifying the particle physics of CDM. Here, we consider an ultra-light scalar field DM particle manifesting a wave nature below a DM particle mass-dependent Jeans scale. For DM mass $m\sim10^{-22}{\rm eV}$, this scenario delays galaxy formation and avoids cusps in the center of the dark matter haloes. We use new measurements of half-light mass in ultra-faint dwarf galaxies Draco II and Triangulum II to estimate the mass of the DM particle in this model. We find that if the stellar populations are within the core of the density profile then the data are in agreement with a wave dark matter model having a DM particle with $m\sim 3.7-5.6\times 10^{-22}{\rm eV}$. The presence of this extremely light particle will contribute to the formation of a central solitonic core replacing the cusp of a Navarro-Frenk-White profile and bringing predictions closer to observations of cored central density in dwarf galaxies.
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We present near infrared (NIR) spectroscopic and photometric observations of the nearby Type Ia SN 2014J. The seventeen NIR spectra span epochs from +15.3 to +92.5 days after $B$-band maximum light, while the $JHK_s$ photometry include epochs from $-$10 to +71 days. This data is used to constrain the progenitor system of SN 2014J utilizing the Pa$\beta$ line, following recent suggestions that this phase period and the NIR in particular are excellent for constraining the amount of swept up hydrogen-rich material associated with a non-degenerate companion star. We find no evidence for Pa$\beta$ emission lines in our post-maximum spectra, with a rough hydrogen mass limit of $\lesssim$0.1 $M_{\odot}$, which is consistent with previous limits in SN 2014J from late-time optical spectra of the H$\alpha$ line. Nonetheless, the growing dataset of high-quality NIR spectra holds the promise of very useful hydrogen constraints.
Intense, compact, star-forming galaxies are rare in the local Universe but ubiquitous at high redshift. We interpret the 0.1-22 um spectral energy distributions (SED) of a sample of 180 galaxies at 0.05<z<0.25 selected for extremely high surface densities of inferred star formation in the ultraviolet. By comparison with well-established stellar population synthesis models we find that our sample comprises young (~ 60 - 400 Myrs), moderate mass (~ $6\times 10^9$ Msun) star-forming galaxies with little dust extinction (mean stellar continuum extinction $E_\mathrm{cont}$(B-V) ~ 0.1) and find star formation rates of a few tens of Solar masses per year. We use our inferred masses to determine a mean specific star formation rate for this sample of ~ $10^{-9}$ yr$^{-1}$, and compare this to the specific star formation rates in distant Lyman break galaxies (LBGs), and in other low redshift populations. We conclude that our sample's characteristics overlap significantly with those of the z~5 LBG population, making ours the first local analogue population well tuned to match those high redshift galaxies. We consider implications for the origin and evolution of early galaxies.
We present radiation hydrodynamic simulations of collapsing protostellar cores with initial masses of 30, 100, and 200 M$_{\odot}$. We follow their gravitational collapse and the formation of a massive protostar and protostellar accretion disk. We employ a new hybrid radiative feedback method blending raytracing techniques with flux-limited diffusion for a more accurate treatment of the temperature and radiative force. In each case, the disk that forms becomes Toomre-unstable and develops spiral arms. This occurs between 0.35 and 0.55 freefall times and is accompanied by an increase in the accretion rate by a factor of 2-10. Although the disk becomes unstable, no other stars are formed. In the case of our 100 and 200 M$_{\odot}$ simulation, the star becomes highly super-Eddington and begins to drive bipolar outflow cavities that expand outwards. These radiatively-driven bubbles appear stable, and appear to be channeling gas back onto the protostellar accretion disk. Accretion proceeds strongly through the disk. After 81.4 kyr of evolution, our 30 M$_{\odot}$ simulation shows a star with a mass of 5.48 M$_{\odot}$ and a disk of mass 3.3 M$_{\odot}$, while our 100 M$_{\odot}$ simulation forms a 28.8 M$_{\odot}$ mass star with a 15.8 M$_{\odot}$ disk over the course of 41.6 kyr, and our 200 M$_{\odot}$ simulation forms a 43.7 M$_{\odot}$ star with an 18 M$_{\odot}$ disk in 21.9 kyr. In the absence of magnetic fields or other forms of feedback, the masses of the stars in our simulation do not appear limited by their own luminosities.
The Gaia archive is being designed and implemented by the DPAC Consortium. The purpose of the archive is to maximize the scientific exploitation of the Gaia data by the astronomical community. Thus, it is crucial to gather and discuss with the community the features of the Gaia archive as much as possible. It is especially important from the point of view of the GENIUS project to gather the feedback and potential use cases for the archive. This paper presents very briefly the general ideas behind the Gaia archive and presents which tools are already provided to the community.
Deep observations of galaxies reveal faint extended stellar components (hereafter ESCs) of streams, shells, and halos. These are a natural prediction of hierarchical galaxy formation, as accreted satellite galaxies are tidally disrupted by their host. We investigate whether or not global properties of the ESC could be used to test of dark matter, reasoning that they should be sensitive to the abundance of low-mass satellites, and therefore the underlying dark matter model. Using cosmological simulations of galaxy formation in the favoured Cold Dark Matter (CDM) and Warm Dark Matter (WDM) models ($m_{\rm WDM}$=0.5,1,2 keV/$c^2$), which suppress the abundance of low-mass satellites, we find that the kinematics and orbital structure of the ESC is consistent across models. However, we find striking differences in its spatial structure, as anticipated -- a factor of $\sim$10 drop in spherically averaged mass density between $\sim$10% and $\sim$75% of the virial radius in the more extreme WDM runs ($m_{\rm WDM}$=0.5, 1 keV/$c^2$) relative to the CDM run. These differences are consistent with the mass assembly histories of the different components, and are present across redshifts. However, even the least discrepant of the WDM models is incompatible with current observational limits on $m_{\rm WDM}$. Importantly, the differences we observe when varying the underlying dark matter are comparable to the galaxy-to-galaxy variation we expect within a fixed dark matter model. This suggests that it will be challenging to place limits on dark matter using only the unresolved spatial structure of the the ESC.
A continuous supersonic flow reactor has been used to measure rate constants for the C + NH3 reaction over the temperature range 50 to 296 K. C atoms were created by the pulsed laser photolysis of CBr4. The kinetics of the title reaction were followed directly by vacuum ultra-violet laser induced fluorescence (VUV LIF) of C loss and through H formation. The experiments show unambiguously that the reaction is rapid at 296 K, becoming faster at lower temperatures, reaching a value of 1.8 10-10 cm3 molecule-1 s-1 at 50 K. As this reaction is not currently included in astrochemical networks, its influence on interstellar nitrogen hydride abundances is tested through a dense cloud model including gas-grain interactions. In particular, the effect of the ortho-to-para ratio of H2 which plays a crucial role in interstellar NH3 synthesis is examined.
Dwarf satellite galaxies are ideal laboratories for identifying particle Dark Matter signals. When advocating limits on particle Dark Matter properties from null searches, it becomes however crucial the level at which the Dark Matter density profile within these systems is constrained by observations. In the limit in which the spherical Jeans equation is assumed to be valid for a given tracer stellar population, we study the solution of this equation having the Dark Matter mass profile as an output rather than as a trial parametric input. Within our new formulation, we address to what level dwarf spheroidal galaxies feature a reliable mass estimator. We assess then possible extrapolation of the density profiles in the inner regions and -- keeping explicit the dependence on the orbital anisotropy profile of the tracer population -- we derive general trends on the line-of-sight integral of the density profile squared, a quantity commonly dubbed $J$-factor and crucial to estimate fluxes from prompt Dark Matter pair annihilations. Taking Ursa Minor as a study case among Milky Way satellites, we perform Bayesian inference using the available kinematical data for this galaxy. Contrary to all previous studies, we avoid to marginalize over quantities poorly constrained by observations or by theoretical arguments. We find minimal $J$-factors to be about 2 to 4 times smaller than commonly quoted estimates, approximately relaxing by the same amount the limit on Dark Matter pair annihilation cross section from gamma-ray surveys of Ursa Minor. At the same time, if one goes back to a fixed trial parametric form for the density, e.g. using a NFW or Burkert profile, we show that the minimal $J$ can hardly be reduced by more than a factor of 1.5.
Radio observations over the last two decades have provided evidence that diffuse synchrotron emission in the form of megaparsec-scale radio halos in galaxy clusters is likely tracing regions of the intracluster medium where relativistic particles are accelerated during cluster mergers. In this paper we present results of a survey of 14 galaxy clusters carried out with the 7-element Karoo Array Telescope at 1.86 GHz, aimed to extend the current studies of radio halo occurrence to systems with lower masses (M$_{\rm 500} > 4\times10^{14}$ M${_\odot}$). We found upper limits at the $0.6 - 1.9 \times 10^{24}$ Watt Hz$^{-1}$ level for $\sim 50\%$ of the sample, confirming that bright radio halos in less massive galaxy clusters are statistically rare.
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