Massive galaxies display extended light profiles that can reach several hundreds of kilo parsecs. These stellar halos provide a fossil record of galaxy assembly histories. Using data that is both wide (~100 square degree) and deep (i>28.5 mag/arcsec^2 in i-band), we present a systematic study of the stellar halos of a sample of more than 3000 galaxies at 0.3 < z < 0.5 with $\log M_{\star}/M_{\odot} > 11.4$. Our study is based on high-quality (0.6 arcsec seeing) imaging data from the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP), which enables us to individually estimate surface mass density profiles to 100 kpc without stacking. As in previous work, we find that more massive galaxies exhibit more extended outer profiles. When this extended light is not properly accounted for as a result of shallow imaging or inadequate profile modeling, the derived stellar mass function can be significantly underestimated at the highest masses. Across our sample, the ellipticity of outer light profiles increases substantially as we probe larger radii. We show for the first time that these ellipticity gradients steepen dramatically as a function of galaxy mass, but we detect no mass-dependence in outer color gradients. Our results support the two-phase formation scenario for massive galaxies in which outer envelopes are built up at late times from a series of merging events. We provide surface mass surface mass density profiles in a convenient tabulated format to facilitate comparisons with predictions from numerical simulations of galaxy formation.
We present a new Bayesian algorithm making use of Markov Chain Monte Carlo sampling that allows us to simultaneously estimate the unknown continuum level of each quasar in an ensemble of high-resolution spectra, as well as their common probability distribution function (PDF) for the transmitted Ly$\alpha$ forest flux. This fully automated PDF regulated continuum fitting method models the unknown quasar continuum with a linear Principal Component Analysis (PCA) basis, with the PCA coefficients treated as nuisance parameters. The method allows one to estimate parameters governing the thermal state of the intergalactic medium (IGM), such as the slope of the temperature-density relation $\gamma-1$, while marginalizing out continuum uncertainties in a fully Bayesian way. Using realistic mock quasar spectra created from a simplified semi-numerical model of the IGM, we show that this method recovers the underlying quasar continua to a precision of $\simeq7\%$ and $\simeq10\%$ at $z=3$ and $z=5$, respectively. Given the number of principal component spectra, this is comparable to the underlying accuracy of the PCA model itself. Most importantly, we show that we can achieve a nearly unbiased estimate of the slope $\gamma-1$ of the IGM temperature-density relation with a precision of $\pm8.6\%$ at $z=3$, $\pm6.1\%$ at $z=5$, for an ensemble of ten mock high-resolution quasar spectra. Applying this method to real quasar spectra and comparing to a more realistic IGM model from hydrodynamical simulations would enable precise measurements of the thermal and cosmological parameters governing the IGM, albeit with somewhat larger uncertainties given the increased flexibility of the model.
The time delays of gravitationally lensed quasars are generally believed to be unique numbers whose measurement is limited only by the quality of the light curves and the models for the contaminating contribution of gravitational microlensing to the light curves. This belief is incorrect -- gravitational microlensing also produces changes in the actual time delays on the ~day(s) light-crossing time scale of the emission region. This is due to a combination of the inclination of the disk relative to the line of sight and the differential magnification of the temperature fluctuations producing the variability. We demonstrate this both mathematically and with direct calculations using microlensing magnification patterns. Measuring these delay fluctuations can provide a physical scale for microlensing observations, removing the need for priors on either the microlens masses or the component velocities. That time delays in lensed quasars are themselves time variable likely explains why repeated delay measurements of individual lensed quasars appear to vary by more than their estimated uncertainties. This effect is also an important new systematic problem for attempts to use time delays in lensed quasars for cosmology or to detect substructures (satellites) in lens galaxies.
To explain the high observed abundances of r-process elements in local ultra- faint dwarf (UFD) galaxies, we perform cosmological zoom simulations that include r-process production from neutron star mergers (NSMs). We model star-formation stochastically and simulate two different halos with total masses $\approx 10^8 M_{\odot}$ at z = 6. We find that the final distribution of [Eu/H] vs. [Fe/H] is relatively insensitive to the energy by which the r-process material is ejected into the interstellar medium, but strongly sensitive to the environment in which the NSM event occurs. In one halo the NSM event takes place at the center of the stellar distribution, leading to high-levels of r-process enrichment such as seen in a local UFD, Reticulum II (Ret II). In a second halo, the NSM event takes place outside of the densest part of the galaxy, leading to a more extended r-process distribution. The subsequent star formation occurs in an interstellar medium with shallow levels of r-process enrichment which results in stars with low levels of [Eu/H] compared to Ret II stars even when the maximum possible r-process mass is assumed to be ejected. This suggests that the natal kicks of neutron stars may also play an important role in determining the r-process abundances in UFD galaxies, a topic that warrants further theoretical investigation.
To reionize the early universe, high-energy photons must escape the galaxies that produce them. It has been suggested that stellar feedback drives galactic outflows out of star-forming regions, creating low density channels through which ionizing photons escape into the inter-galactic medium. We compare the galactic outflow properties of confirmed Lyman continuum (LyC) leaking galaxies to a control sample of nearby star-forming galaxies to explore whether the outflows from leakers are extreme as compared to the control sample. We use data from the Cosmic Origins Spectrograph on the Hubble Space Telescope to measure the equivalent widths and velocities of Si II and Si III absorption lines, tracing neutral and ionized galactic outflows. We find that the Si II and Si III equivalent widths of the LyC leakers reside on the low-end of the trend established by the control sample. The leakers' velocities are not statistically different than the control sample, but their absorption line profiles have a different asymmetry: their central velocities are closer to their maximum velocities. The outflow kinematics and equivalent widths are consistent with the scaling relations between outflow properties and host galaxy properties -- most notably metallicity -- defined by the control sample. Additionally, we use the Ly\alpha\ profiles to show that the Si II equivalent width scales with the Ly\alpha\ peak velocity separation. We determine that the low equivalent widths of the leakers are likely driven by low metallicities and low H I column densities, consistent with a density-bounded ionization region, although we cannot rule out significant variations in covering fraction. While we do not find that the LyC leakers have extreme outflow velocities, the low maximum-to-central velocity ratios demonstrate the importance of the acceleration and density profiles for LyC and Ly\alpha\ escape. [abridged]
We investigate galaxy conformity using the {\sc Mufasa}\ cosmological hydrodynamical simulation, which uses a heuristic halo mass-based prescription to quench central galaxies. We show that satellite galaxies are broadly consistent with observations, showing a bimodal distribution in colour with radius, albeit with too many low-mass quenched satellites. In {\sc Mufasa}, galaxy conformity is evident in previously observed properties such as colour, specific star formation rate, and {\sc Hi}\ content, as well as in environment, stellar age, H$_2$ content, and metallicity. We introduce quantifying conformity using a new measure ${\cal S}(R)$, and show that low-mass haloes have weak conformity extending to large projected radii $R$ in all properties, while high-mass haloes have strong conformity that diminishes rapidly with $R$ and disappears at $R\ga 1$~Mpc. ${\cal S}(R)$ is strongest for environment in low-mass haloes, and sSFR (or colour) in high-mass haloes, and is dominated by one-halo conformity with the exception of {\sc Mufasa}\ in small haloes. Metallicity shows a curious anti-conformity in massive haloes. Tracking the evolution of conformity for $z=0$ galaxies back in time shows that conformity generally emerges as a late-time phenomenon. However, for fixed halo mass bins, conformity is fairly constant with redshift out to $z\ga 2$. These trends are consistent with the idea that strong conformity only emerges once haloes grow above {\sc Mufasa}'s quenching mass scale of $\sim 10^{12}M_\odot$. A quantitative measure of conformity in various properties, along with its evolution, thus represents a new and stringent test of the impact of quenching on environment within current galaxy formation models.
We present Herschel SPIRE-FTS intermediate-sampled mapping observations of the central ~8 kpc (~150") of M51, with a spatial resolution of 40". We detect 4 12CO transitions (J=4-3 to J=7-6) and the CI 3P2-3P1 and 3P1-3P0 transitions. We supplement these observations with ground based observations of 12CO J=1-0 to J=3-2 and perform a two-component non-LTE analysis. We find that the molecular gas in the nucleus and centre regions has a cool component (T_kin~10-20 K) with a moderate but poorly constrained density (n(H2)~10^3-10^6 cm^-3), as well as significant molecular gas in a warmer (T_kin~300-3000 K), lower density (n(H2)~10^1.6-10^2.5 cm^-3) component. We compare our CO line ratios and calculated densities along with ratios of CO to total infrared luminosity to a grid of photon dominated region (PDR) models and find that the cold molecular gas likely resides in PDRs with a field strength of G_o~10^2. The warm component likely requires an additional source of mechanical heating, from supernovae and stellar winds or possibly shocks produced in the strong spiral density wave. When compared to similar two-component models of other star-forming galaxies published as part of the Very Nearby Galaxies Survey (Arp 220, M82 and NGC 4038/39), M51 has the lowest density for the warm component, while having a warm gas mass fraction that is comparable to those of Arp 220 and M82, and significantly higher than that of NGC 4038/39.
We study the dependence of galaxy clustering on atomic gas mass using a sample of $\sim$16,000 galaxies with redshift in the range of $0.0025<z<0.05$ and HI mass of $M_{\rm HI}>10^8M_{\odot}$, drawn from the 70% complete sample of the Arecibo Legacy Fast ALFA survey. We construct subsamples of galaxies with $M_{\rm HI}$ above different thresholds, and make volume-limited clustering measurements in terms of three statistics: the projected two-point correlation function, the projected cross-correlation function with respect to a reference sample selected from the Sloan Digital Sky Survey, and the redshift-space monopole moment. In contrast to previous studies, which found no/weak HI-mass dependence, we find both the clustering amplitude on scales above a few Mpc and the bias factors to increase significantly with increasing HI mass for subsamples with HI mass thresholds above $10^9M_{\odot}$. For HI mass thresholds below $10^9M_{\odot}$, while the measurements have large uncertainties caused by the limited survey volume and sample size, the inferred galaxy bias factors are systematically lower than the minimum halo bias factor from mass-selected halo samples. The simple halo model, in which galaxy content is only determined by halo mass, has difficulties in interpreting the clustering measurements of the HI-selected samples. We extend the simple model by including the halo formation time as an additional parameter. A model that puts HI-rich galaxies into halos that formed late can reproduce the clustering measurements reasonably well. We present the implications of our best-fitting model on the correlation of HI mass with halo mass and formation time, as well as the halo occupation distributions and HI mass functions for central and satellite galaxies. These results are compared with the predictions from semi-analytic galaxy formation models and hydrodynamic galaxy formation simulations.
The Galaxy Zoo has provided morphological data on many galaxies. Several biases have been identified in the Galaxy Zoo data. Here we report on a newly discovered selection effect: astronomers interested in studying spiral galaxies may select a set of spiral galaxies based upon a threshold in spirality (the fraction of Galaxy Zoo humans who report seeing spiral structure). SpArcFiRe is an automated tool that decomposes a spiral galaxy into its constituent spiral arms, providing objective, quantitative data on their structure. SpArcFiRe measures the pitch angle of spiral arms. We have observed that when selecting a set of spiral galaxies based on a threshold on spirality, the pitch angle of spiral arms appear increase with redshift. We hypothesize that this is a selection effect: tightly-wound spiral arms become less visible as images degrade with increasing redshift, leading to fewer such galaxies being included in the sample at higher redshifts. We corroborate this hypothesis by artificially degrading images of nearby galaxies, then using a machine learning algorithm trained on Galaxy Zoo data to provide a spirality for each artificially degraded image. It correctly predicts that spirality decreases as image quality degrades. Thus, the mean pitch angle of those galaxies remaining above the spirality threshold is higher than those eliminated by the selection effect. This demonstrates that users who select samples of galaxies using a threshold of Galaxy Zoo votes must carefully consider the possibility of selection effects on morphological measures, even if the measure itself is believed to be objective and unbiased. Finally, we also perform an empirical sensitivity analysis to demonstrate that SpArcFiRe's output changes in a smooth and predictable fashion to changes in its internal algorithmic parameters.
Recent observations suggest that intensive molecular cloud collision can trigger massive star/cluster formation. The most important physical process caused by the collision is a shock compression. In this paper, the influence of a shock wave on the evolution of a molecular cloud is studied numerically by using isothermal magnetohydrodynamics (MHD) simulations with the effect of self-gravity. Adaptive-mesh-refinement and sink particle techniques are used to follow long-time evolution of the shocked cloud. We find that the shock compression of turbulent inhomogeneous molecular cloud creates massive filaments, which lie perpendicularly to the background magnetic field as we have pointed out in a previous paper. The massive filament shows global collapse along the filament, which feeds a sink particle located at the collapse center. We observe high accretion rate dot{M}_acc > 10^{-4} M_sun/yr that is high enough to allow the formation of even O-type stars. The most massive sink particle achieves M>50 M_sun in a few times 10^5 yr after the onset of the filament collapse.
PHL 6625 is a luminous quasi-stellar object (QSO) at z = 0.3954 located behind the nearby galaxy NGC 247 (z = 0.0005). Hubble Space Telescope (HST) observations revealed an arc structure associated with it. We report on spectroscopic observations with the Very Large Telescope (VLT) and multiwavelength observations from the radio to the X-ray band for the system, suggesting that PHL 6625 and the arc are a close pair of merging galaxies, instead of a strong gravitational lens system. The QSO host galaxy is estimated to be (4-28) x 10^10 M_sun, and the mass of the companion galaxy of is estimated to be M_* = (6.8 +/- 2.4) x 10^9 M_sun, suggesting that this is a minor merger system. The QSO displays typical broad emission lines, from which a black hole mass of about (2-5) x 10^8 M_sun and an Eddington ratio of about 0.01-0.05 can be inferred. The system represents an interesting and rare case where a QSO is associated with an ongoing minor merger, analogous to Arp 142.
Barnett relaxation, first described by Purcell in 1979, appears to play a major role in the alignment of grains with the interstellar magnetic field. In 1999, Lazarian and Draine proposed that Barnett relaxation and its relative, nuclear relaxation, can induce grains to flip. If this thermal flipping is rapid, then the dynamical effect of torques that are fixed relative to the grain body can be greatly reduced. To date, detailed studies of Barnett relaxation have been confined to grains exhibiting dynamic symmetry. In 2003, Weingartner argued that internal relaxation cannot induce flips in any grains, whether they exhibit dynamic symmetry or not. In this work, we develop approximate expressions for the dissipation rate and diffusion coefficient for Barnett relaxation. We revisit the issue of internally induced thermal flipping, finding that it cannot occur for grains with dynamic symmetry but does occur for grains lacking dynamic symmetry.
Aims. We wish to clarify the origin of the multiple jet features emanating from the binary protostar SVS 13A (= VLA4A/VLA4B). Methods. We used the Plateau de Bure Interferometer to map at 0.3-0.8" (~70-190 au) dust emission at 1.4 mm, CO(2-1), SiO(5-4), SO(65-54). Revised proper motions for VLA4A/4B and jet wiggling models are computed to clarify their respective contribution. Results. VLA4A shows compact dust emission suggestive of a disk < 50 au, and is the hot corino source, while CO/SiO/SO counterparts to the small-scale H2 jet originate from VLA4B and reveal the jet variable velocity structure. This jet exhibits ~ 3" wiggling consistent with orbital motion around a yet undetected ~ 20-30 au companion to VLA4B, or jet precession. Jet wiggling combined with velocity variability can explain the large apparent angular momentum in CO bullets. We also uncover a synchronicity between CO jet bullets and knots in the HH7-11 chain demonstrating that they trace two distinct jets. Their ~ 300 yr twin outburst period may be triggered by close perihelion approach of VLA4A in an eccentric orbit around VLA4B. A third jet is tentatively seen at PA ~ 0 degrees. Conclusions. SVS13 A harbors at least 2 and possibly 3 distinct jet sources. The CO and HH7-11 jets are launched from quasi-coplanar disks, separated by 20-70 au. Their synchronous major events every 300 yr favor external triggering by close binary interactions, a scenario also invoked for FU Or outbursts.
We report the discovery of an extremely large (R_b ~ 2"77 ~ 4.2 kpc) core in the brightest cluster galaxy, IC 1101, of the rich galaxy cluster Abell 2029. Luminous core-S\'ersic galaxies contain depleted cores---with sizes (R_b) typically 20 - 500 pc---that are thought to be formed by coalescing black hole binaries. We fit a (double nucleus) + (spheroid) + (intermediate-scale component) + (stellar halo) model to the HST surface brightness profile of IC 1101, finding the largest core size measured in any galaxy to date. This core is an order of magnitude larger than those typically measured for core-S\'ersic galaxies. We find that the spheroid's V-band absolute magnitude (M_V) of -23.8 mag (~ 25% of the total galaxy light, i.e., including the stellar halo) is faint for the large R_b, such that the observed core is 1.02 dex ~ 3.4 sigma_s (rms scatter) larger than that estimated from the R_ b -M_V relation. The suspected scouring process has produced a large stellar mass deficit (M_def) ~ 4.9 X 10^11 M_sun, i.e., a luminosity deficit ~ 28% of the spheroid's luminosity prior to the depletion. Using IC 1101's black hole mass (M_BH) estimated from the M_BH-$\sigma$, M_BH-L and M_BH-M_* relations, we measure an excessive and unrealistically high number of dry major mergers for IC 1101 (i.e., $\mathcal{N} \ga 76$) as traced by the large M_def/M_ BH ratios of 38-101. The large core, high mass deficit and oversized M_def/M_ BH ratio of IC 1101 suggest that the depleted core was scoured by overmassive SMBH binaries with a final coalesced mass M_BH ~ (4 -10) X 10^10 M_sun, i.e., ~ (1.7- 3.2) X sigma_s larger than the black hole masses estimated using the spheroid's $\sigma$, L and M_*. The large core might be partly due to oscillatory core passages by a gravitational radiation-recoiled black hole.
Milagro observations have found bright, diffuse TeV emission concentrated along the galactic plane of the Milky Way. The intensity and spectrum of this emission is difficult to explain with current models where gamma-ray production is dominated by hadronic mechanisms, and has been named the "TeV excess". We show that TeV emission from pulsars naturally explains this excess. In particular, recent observations have detected "TeV halos" surrounding pulsars that are either nearby or particularly luminous. Here, we show that the full population of Milky Way pulsars will produce diffuse TeV emission concentrated along the Milky Way plane. The total gamma-ray flux from TeV halos is expected to exceed the hadronic gamma-ray flux at energies above ~500 GeV. Moreover, the spectrum and intensity of TeV halo emission naturally matches the TeV excess. If this scenario is common to all galaxies, it will decrease the contribution of star-forming galaxies to the IceCube neutrino flux. Finally, we show that upcoming HAWC observations will resolve a significant fraction of the TeV excess into individual TeV halos, conclusively confirming, or ruling out, this model.
We present HR Diagrams for the massive star populations in M31 and M33 including several different types of emission-line stars: the confirmed Luminous Blue Variables (LBVs), candidate LBVs, B[e] supergiants and the warm hypergiants. We estimate their apparent temperatures and luminosities for comparison with their respective massive star populations and to evaluate the possible relationships of these different classes of evolved, massive stars, and their evolutionary state. Several of the LBV candidates lie near the LBV/S Dor instability strip which supports their classification. Most of the B[e] supergiants, however, are less luminous than the LBVs. Many are very dusty with the infrared flux contributing one-third or more to their total flux. They are also relatively isolated from other luminous OB stars. Overall, their spatial distribution suggests a more evolved state. Some may be post-RSGs like the warm hypergiants, and there may be more than one path to becoming a B[e] star. There are sufficient differences in the spectra, luminosities, spatial distribution, and the presence or lack of dust between the LBVs and B[e] supergiants to conclude that one group does not evolve into the other.
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We present new Adaptive Optics (AO) imaging and spectroscopic measurements of Galactic Center source G1 from W. M. Keck Observatory. Our goal is to understand its nature and relationship to G2, which is the first example of a spatially-resolved object interacting with the supermassive black hole (SMBH). Both objects have been monitored with AO for the past decade (2003 - 2014) and are comparatively close to the black hole ($a_{\rm{min}} \sim$200-300 AU) on very eccentric orbits ($e_{\rm{G1}}\sim$0.99; $e_{\rm{G2}}\sim$0.96). While G2 has been tracked before and during periapse passage ($T_{0} \sim$ 2014.2), G1 has been followed since soon after emerging from periapse ($T_{0} \sim$ 2001.3). Our observations of G1 double the previously reported observational time baseline, which improves its orbital parameter determinations. G1's orbital trajectory appears to be in the same plane as that of G2, but with a significantly different argument of periapse ($\Delta\omega$ = 21$\pm$4 degrees). This suggests that G1 is an independent object and not part of a gas stream containing G2 as has been proposed. Furthermore, we show for the first time that: (1) G1 is extended in the epochs closest to periapse along the direction of orbital motion and (2) G1 becomes significantly smaller over time, (450 AU in 2004 to less than 170 AU in 2009). Based on these observations, G1 appears to be the second example of an object tidally interacting with a SMBH. G1's existence 14 years after periapse, along with its compactness in epochs further from the time of periapse, suggest that this source is stellar in nature.
We analyse the velocity dispersion properties of 472 z~0.9 star-forming galaxies observed as part of the KMOS Redshift One Spectroscopic Survey (KROSS). The majority of this sample is rotationally dominated (83 +/- 5% with v_C/sigma_0 > 1) but also dynamically hot and highly turbulent. After correcting for beam smearing effects, the median intrinsic velocity dispersion for the final sample is sigma_0 = 43.2 +/- 0.8 km/s with a rotational velocity to dispersion ratio of v_C/sigma_0 = 2.6 +/- 0.1. To explore the relationship between velocity dispersion, stellar mass, star formation rate and redshift we combine KROSS with data from the SAMI survey (z~0.05) and an intermediate redshift MUSE sample (z~0.5). While there is, at most, a weak trend between velocity dispersion and stellar mass, at fixed mass there is a strong increase with redshift. At all redshifts, galaxies appear to follow the same weak trend of increasing velocity dispersion with star formation rate. Our results are consistent with an evolution of galaxy dynamics driven by disks that are more gas rich, and increasingly gravitationally unstable, as a function of increasing redshift. Finally, we test two analytic models that predict turbulence is driven by either gravitational instabilities or stellar feedback. Both provide an adequate description of the data, and further observations are required to rule out either model.
The nearby dwarf galaxy NGC404 harbors a low-luminosity active galactic nucleus (AGN) powered by the lowest-mass (< 150,000 solar-masses) central massive black hole (MBH) with a dynamical mass constraint currently known, thus providing a rare low-redshift analog to the MBH "seeds" that formed in the early Universe. Here, we present new imaging of the nucleus of NGC404 at 12-18 GHz with the Karl G. Jansky Very Large Array (VLA) and observations of the CO(2-1) line with the Atacama Large Millimeter/Submillimeter Array (ALMA). For the first time, we have successfully resolved the nuclear radio emission, revealing a centrally peaked, extended source spanning 17 pc. Combined with previous VLA observations, our new data place a tight constraint on the radio spectral index and indicate an optically-thin synchrotron origin for the emission. The peak of the resolved radio source coincides with the dynamical center of NGC404, the center of a rotating disk of molecular gas, and the position of a compact, hard X-ray source. We also present evidence for shocks in the NGC404 nucleus from archival narrowband HST imaging, Chandra X-ray data, and Spitzer mid-infrared spectroscopy, and discuss possible origins for the shock excitation. Given the morphology, location, and steep spectral index of the resolved radio source, as well as constraints on nuclear star formation from the ALMA CO(2-1) data, we find the most likely scenario for the origin of the radio source in the center of NGC404 to be a radio outflow associated with a confined jet driven by the active nucleus.
We identify six new CEMP stars ([C/Fe]>+0.7 and [Fe/H]< -1.8) and another seven likely candidates within the APOGEE database following Data Release 12. These stars have chemical compositions typical of metal-poor halo stars, e.g., mean [$\alpha$/Fe] = +0.24$\pm$0.24, based on the ASPCAP pipeline results. A lack of heavy element spectral lines impedes further sub-classification of these CEMP stars, however, based on radial velocity scatter, we predict most are not CEMP-s stars which are typically found in binary systems. Only one object, 2M15312547+4220551, may be in a binary since it exhibits a scatter in its radial velocity of 1.7 $\pm$0.6 km s$^{-1}$ based on three visits over a 25.98 day baseline. Optical observations are now necessary to confirm the stellar parameters and low metallicities of these stars, to determine the heavy-element abundance ratios and improve the precision in the derived abundances, and to examine their CEMP sub-classifications.
We present our new, fully-automated method to detect and measure the ages of star clusters in nearby galaxies, where individual stars can be resolved. The method relies purely on statistical analysis of observations and Monte-Carlo simulations to define stellar overdensities in the data. It decontaminates the cluster color-magnitude diagrams and, using a revised version of the Bayesian isochrone fitting code of Ramirez-Siordia et al., estimates the ages of the clusters. Comparisons of our estimates with those from other surveys show the superiority of our method to extract and measure the ages of star clusters, even in the most crowded fields. An application of our method is shown for the high-resolution, multi-band imaging of the Large Magellanic Cloud. We detect 4850 clusters in the 7 deg2 we surveyed, 3451 of which have not been reported before. Our findings suggest multiple epochs of star cluster formation, with the most probable occurring ~310 Myr ago. Several of these events are consistent with the epochs of the interactions among the Large and Small Magellanic Clouds, and the Galaxy, as predicted by N-body numerical simulations. Finally, the spatially resolved star cluster formation history may suggest an inside-out cluster formation scenario throughout the LMC, for the past 1 Gyr.
We improve on the model of the Galactic Magnetic Field (GMF) from Jansson \& Farrar (2012), which was constrained using all-sky rotation measures of extragalactic sources and polarized and unpolarized synchrotron emission data from WMAP. We have developed several alternative functional forms for the coherent and random components, used newer synchrotron products from Planck and WMAP and testes new models of the densities of thermal electrons and cosmic-ray electrons. The differences in the resultant GMF models, depending on which parameterization of the field, synchrotron product and electron densities are used, provides a measure of the uncertainty in our inference of the GMF. We discuss the impact of these uncertainties on charged-particle astronomy at ultra-high energies.
We present a study of the three-dimensional structure of the molecular clouds in the Galactic Centre (GC) using CO emission and OH absorption lines. Two CO isotopologue lines, $^{12}$CO ($J$=1$\rightarrow$0) and $^{13}$CO ($J$=1$\rightarrow$0), and four OH ground-state transitions, surveyed by the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH), contribute to this study. We develop a novel method to calculate the OH column density, excitation temperature, and optical depth precisely using all four OH lines, and we employ it to derive a three-dimensional model for the distribution of molecular clouds in the GC for six slices in Galactic latitude. The angular resolution of the data is 15.5 arcmin, which at the distance of the GC (8.34 kpc) is equivalent to 38 pc. We find that the total mass of OH in the GC is in the range 2400-5100 Solar mass . The face-on view at a Galactic latitude of b = 0{\deg} displays a bar-like structure with an inclination angle of 67.5 $\pm$ 2.1{\deg} with respect to the line of sight. No ring-like structure in the GC is evident in our data, likely due to the low spatial resolution of the CO and OH maps.
A massive galaxy cluster can serve as a magnifying glass for distant stellar populations, with strong gravitational lensing exposing details in the lensed background galaxies that would otherwise be undetectable. The MACS J0416.1-2403 cluster (hereafter MACS0416) is one of the most efficient lenses in the sky, and in 2014 it was observed with high-cadence imaging from the Hubble Space Telescope (HST). Here we describe two unusual transient events that appeared behind MACS0416 in a strongly lensed galaxy at redshift $z = 1.0054 \pm 0.0002$. These transients---designated HFF14Spo-NW and HFF14Spo-SE and collectively nicknamed "Spock"---were faster and fainter than any supernova (SN), but significantly more luminous than a classical nova. They reached peak luminosities of $\sim10^{41}$ erg s$^{-1}$ ($M_{\rm AB} < -14$ mag) in 5 rest-frame days, then faded below detectability in roughly the same time span. Models of the cluster lens suggest that these events may be spatially coincident at the source plane, but are most likely not temporally coincident. We find that HFF14Spo can be explained as a luminous blue variable (LBV), a recurrent nova (RN), or a pair of stellar microlensing events. To distinguish between these hypotheses will require a clarification of the positions of nearby critical curves, along with high-cadence monitoring of the field that could detect new transient episodes in the host galaxy.
We report an ultra-bright lensed submillimeter galaxy (SMG) at $z=2.0439$, {\it WISE} J132934.18+224327.3, identified as a result of a full-sky cross-correlation of the {\it AllWISE} and {\it Planck} compact source catalogs aimed to search for bright analogs of the submillimeter galaxy SMMJ2135, the Cosmic Eyelash. Inspection of archival SCUBA-2 observations of the candidates revealed a source with fluxes (S$_{850 \mu m}$= 130 mJy) consistent with the {\it Planck} measurements. The centroid of the SCUBA-2 source coincides within 1 arcsec with the position of the {\it AllWISE} mid-IR source, and, remarkably, with an arc shaped lensed galaxy in {\it HST} images at visible wavelengths. Low-resolution rest-frame UV-optical spectroscopy of this lensed galaxy obtained with 10.4 m GTC reveals the typical absorption lines of a starburst galaxy. Gemini-N near-IR spectroscopy provided a clear detection of H$_{\alpha}$ emission. The lensed source appears to be gravitationally magnified by a massive foreground galaxy cluster lens at $z = 0.44$, modeling with Lenstool indicates a lensing amplification factor of $11\pm 2$. We determine an intrinsic rest-frame 8-1000-$\mu$m luminosity, $L_{\rm IR}$, of $(1.3 \pm 0.1) \times 10^{13}$ $L_\sun$, and a likely star-formation rate (SFR) of $\sim 500-2000$ $M_\sun yr^{-1}$. The SED shows a remarkable similarity with the Cosmic Eyelash from optical-mid/IR to sub-millimeter/radio, albeit at higher fluxes.
Dissipative dark matter, where dark matter particle properties closely resemble familiar baryonic matter, is considered. Mirror dark matter, which arises from an isomorphic hidden sector, is a specific and theoretically constrained scenario. Other possibilities include models with more generic hidden sectors that contain massless dark photons (unbroken $U(1)$ gauge interactions). Such dark matter not only features dissipative cooling processes, but is also assumed to have nontrivial heating sourced by ordinary supernovae (facilitated by the kinetic mixing interaction). The dynamics of dissipative dark matter halos around rotationally supported galaxies, influenced by heating as well as cooling processes, can be modelled by fluid equations. For a sufficiently isolated galaxy with stable star formation rate, the dissipative dark matter halos are expected to evolve to a steady state configuration which is in hydrostatic equilibrium and where heating and cooling rates locally balance. Here, we take into account all major cooling and heating processes, and numerically solve for the steady state solution under the assumptions of spherical symmetry and negligible dark magnetic fields. For the parameters considered, we were unable to find a physically realistic solution for the constrained case of mirror dark matter halos. Halo cooling generally exceeds heating at realistic halo mass densities. This problem can be rectified in more generic dissipative dark matter models, and we discuss a specific example in some detail.
We present new proper motion (PM) measurements of the dwarf spheroidal galaxies (dSphs) Draco and Sculptor using multi-epoch images obtained with the Hubble Space Telescope ACS/WFC. Our PM results have uncertainties far lower than previous measurements (even made with the same instrument) thanks to the long time-baseline of 9-11 years. (abridged due to arXiv abstract limit) We study the detailed orbital history of both Draco and Sculptor via numerical orbit integrations. Orbital periods of Draco and Sculptor are found to be 1-2 and 2--5 Gyrs, respectively, accounting for uncertainties in the MW mass. We also study the influence of the Large Magellanic Cloud (LMC) on the orbits of Draco and Sculptor. Overall, the inclusion of the LMC increases the scatter in the orbital results. Based on our calculations for a plausible ranges of masses for the MW and the LMC, Draco and Sculptor have likely been orbiting around the MW for the past 6 Gyr, but we can not completely rule out a scenario where Draco and/or Sculptor are on their first infall towards the MW. Whereas Draco shows a rather wide range of orbital parameters depending on the MW mass and inclusion/exclusion of the LMC, Sculptor's orbit is very well constrained with its most recent pericentric approach to the MW being 0.3-0.4 Gyr ago. Our new PMs imply that the orbital trajectories of both Draco and Sculptor are confined within the Disk of Satellites (DoS), better so than implied by earlier PM measurements, and likely rule out the possibility that these two galaxies were accreted together as part of a tightly bound group.
The sizes of entire systems of globular clusters (GCs) depend on the formation and destruction histories of the GCs themselves, but also on the assembly, merger and accretion history of the dark matter (DM) haloes that they inhabit. Recent work has shown a linear relation between total mass of globular clusters in the globular cluster system and the mass of its host dark matter halo, calibrated from weak lensing. Here we extend this to GC system sizes, by studying the radial density profiles of GCs around galaxies in nearby galaxy groups. We find that radial density profiles of the GC systems are well fit with a de Vaucouleurs profile. Combining our results with those from the literature, we find tight relationship ($\sim 0.2$ dex scatter) between the effective radius of the GC system and the virial radius (or mass) of its host DM halo. The steep non-linear dependence of this relationship ($R_{e, GCS} \propto R_{200}^{2.5 - 3}$) is currently not well understood, but is an important clue regarding the assembly history of DM haloes and of the GC systems that they host.
The probability distribution function of column density (PDF) has become the tool of choice for cloud structure analysis and star formation studies. Its simplicity is attractive, and the PDF could offer access to cloud physical parameters otherwise difficult to measure, but there has been some confusion in the literature on the definition of its completeness limit and shape at the low column density end. In this Letter we use the natural definition of the completeness limit of a column density PDF, the last closed column-density contour inside a surveyed region, and apply it to a set of large-scale maps of nearby molecular clouds. We conclude that there is no observational evidence for log-normal PDFs in these objects. We find that all studied molecular clouds have PDFs well described by power-laws, including the diffuse cloud Polaris. Our results call for a new physical interpretation for the shape of the column density PDFs. We find that the slope of a cloud PDF is invariant to distance but not to the spatial arrangement of cloud material, and as such it is still a useful tool to investigate cloud structure.
We analysed the centre of NGC 1566, which hosts a well-studied active galactic nucleus (AGN), known for its variability. With the aid of techniques such as Principal Component Analysis Tomography, analysis of the emission-line spectra, channel maps, Penalized Pixel Fitting and spectral synthesis applied to the optical and near-infrared data cubes, besides the analysis of Hubble Space Telescope images, we found that: (1) the AGN has a Seyfert 1 emission, with a very strong featureless continuum that we described as a power law with spectral index of 1.7. However, this emission may come not only from the AGN [as its point spread function (PSF) is broader than the PSF of the broad-line region (BLR)], but from hot and young stars, the same ones that probably account for the observed sigma-drop. (2) There is a correlation between redshift and the full width at half-maximum of the BLR emission lines. With a simple model assuming gravitational redshift, we described it as an emitting ring with varying emitting radii and small inclination angles. (3) There is an H II region close to the AGN, which is composed of many substructures forming an apparent spiral with a velocity gradient. (4) We also detected a probable outflow coming from the AGN and it seems to contaminate the H II region emission. (5) We identified an H2 rotating disc with orientation approximately perpendicular to this outflow. This suggests that the rotating disc is an extension of an inner torus/disc structure, which collimates the outflow emission, according to the Unified Model.
It is known that some active galactic nuclei (AGNs) transited from type 1 to type 2 or vice versa. There are two explanations for the so-called changing look AGNs: one is the dramatic change of the obscuration along the line-of-sight, the other is the variation of accretion rate. In this paper, we report the detection of large amplitude variations in the mid-infrared luminosity during the transitions in 10 changing look AGNs using WISE and newly released NEOWISE-R data. The mid-infrared light curves of 10 objects echoes the variability in the optical band with a time lag expected for dust reprocessing. The large variability amplitude is inconsistent with the scenario of varying obscuration, rather supports the scheme of dramatic change in the accretion rate.
High velocity gas that does not conform to Galactic rotation is observed throughout the Galaxy's halo. One component of this gas, HI high velocity clouds (HVCs), have attracted attention since their discovery in the 1960s and remain controversial in terms of their origins, largely due to the lack of reliable distance estimates. The recent discovery of enhanced magnetic fields towards HVCs has encouraged us to explore their connection to cloud evolution, kinematics, and survival as they fall through the magnetized Galactic halo. For a reasonable model for the halo magnetic field, most infalling clouds see transverse rather than radial field lines. We find that significant compression (and thereby amplification) of the ambient magnetic field occurs in front of the cloud and in the tail of material stripped from the cloud. The compressed transverse field attenuates hydrodynamical instabilities. This delays cloud destruction, though not indefinitely. The observed B-field compression is related to the cloud's distance from the Galactic plane. As a result, the observing a rotation measure signal with radio continuum polarization provides useful distance information on a cloud's location.
We investigate the dynamical evolution of isolated equal-mass star cluster models by means of direct N-body simulations, primarily focusing on the effects of the presence of primordial anisotropy in the velocity space. We found evidence of the existence of a monotonic relationship between the moment of core collapse and the amount and flavour of anisotropy in the stellar system. Specifically, equilibria characterised by the same initial structural properties (Plummer density profile) and with different degrees of tangentially-biased (radially-biased) anisotropy, reach core collapse earlier (later) than isotropic models. We interpret this result in light of an accelerated (delayed) phase of the early evolution of collisional stellar systems "anisotropic-response"), which we have characterised both in terms of the evolution of the velocity moments and of a fluid model of two-body relaxation. For the case of the most tangentially anisotropic model the initial phase of evolution involves a catastrophic collapse of the inner part of the system which continues until an isotropic velocity distribution is reached. This study represents a first step towards a comprehensive investigation of the role played by kinematic richness in the long-term dynamical evolution of collisional systems.
We have carried a detailed analysis on the impact of cosmological redshift in the non-parametric approach to automated galaxy morphology classification. We artificially redshifted each galaxy from the EFIGI 4458 sample (re-centered at $z\sim 0$) simulating SDSS, DES, LSST, and HST instruments setups over the range $0 < z < 1.5$. We then traced how the morphometry is degraded in each $z$ using \textsc{Morfometryka}. In the process we re-sampled all catalog to several resolutions and to a diverse SNR range, allowing us to understand the impact of image sampling and noise on our measurements separately. We summarize by exploring the impact of these effects on our capacity to perform automated galaxy supervised morphological classification by investigating the degradation of our classifier's metrics as a function of redshift for each instrument. The overall conclusion is that we can make reliable classification with \textsc{Morfometryka} for $z< 0.2$ with SDSS, for $z<0.5$ with DES, for $z<0.8$ with LSST and for at least $z < 1.5$ with HST.
Molecular clouds are the principle stellar nurseries of our universe, keeping them in the focus of both observational and theoretical studies. From observations, some of the key properties of molecular clouds are well known but many questions regarding their evolution and star formation activity remain open. While numerical simulations feature a large number and complexity of involved physical processes, this plenty of effects may hide the fundamentals that determine the evolution of molecular clouds and enable the formation of stars. Purely analytical models, on the other hand, tend to suffer from rough approximations or a lack of completeness, limiting their predictive power. In this paper, we present a model that incorporates central concepts of astrophysics as well as reliable results from recent simulations of molecular clouds and their evolutionary paths. Based on that, we construct a self-consistent semi-analytical framework that describes the formation, evolution and star formation activity of molecular clouds, including a number of feedback effects to account for the complex processes inside those objects. The final equation system is solved numerically but at much lower computational expense than, e.g., hydrodynamical descriptions of comparable systems. The model presented in this paper agrees well with a broad range of observational results, showing that molecular cloud evolution can be understood as an interplay between accretion, global collapse, star formation and stellar feedback.
Polarized emission from aligned dust is a crucial tool for studies of magnetism in the ISM and a troublesome contaminant for studies of CMB polarization. In each case, an understanding of the significance of the polarization signal requires well-calibrated physical models of dust grains. Despite decades of progress in theory and observation, polarized dust models remain largely underconstrained. During its 2012 flight, the balloon-borne telescope BLASTPol obtained simultaneous broad-band polarimetric maps of a translucent molecular cloud at 250, 350, and 500 microns. Combining these data with polarimetry from the Planck 850 micron band, we have produced a submillimeter polarization spectrum for a cloud of this type for the first time. We find the polarization degree to be largely constant across the four bands. This result introduces a new observable with the potential to place strong empirical constraints on ISM dust polarization models in a previously inaccessible density regime. Comparing with models by Draine and Fraisse (2009), our result disfavors two of their models for which all polarization arises due only to aligned silicate grains. By creating simple models for polarized emission in a translucent cloud, we verify that extinction within the cloud should have only a small effect on the polarization spectrum shape compared to the diffuse ISM. Thus we expect the measured polarization spectrum to be a valid check on diffuse ISM dust models. The general flatness of the observed polarization spectrum suggests a challenge to models where temperature and alignment degree are strongly correlated across major dust components.
We report serendipitous detections of line emission with ALMA in band 3, 6, and 7 in the central parsec of the Galactic center at an up to now highest resolution (<0.7''). Among the highlights are the very first and highly resolved images of sub-mm molecular emission of CS, H13CO+, HC3N, SiO, SO, C2H, and CH3OH in the immediate vicinity (~1'' in projection) of Sgr A* and in the circumnuclear disk (CND). The central association (CA) of molecular clouds shows three times higher CS/X (X: any other observed molecule) luminosity ratios than the CND suggesting a combination of higher excitation - by a temperature gradient and/or IR-pumping - and abundance enhancement due to UV- and/or X-ray emission. We conclude that the CA is closer to the center than the CND is and could be an infalling clump consisting of denser cloud cores embedded in diffuse gas. Moreover, we identified further regions in and outside the CND that are ideally suited for future studies in the scope of hot/cold core and extreme PDR/XDR chemistry and consequent star formation in the central few parsecs.
The lines-of-sight to highly reddened SNe Ia show peculiar continuum polarization curves, growing toward blue wavelengths and peaking at $\lambda_{max} \lesssim 0.4 \mu m$, like no other sight line to any normal Galactic star. We examined continuum polarization measurements of a sample of asymptotic giant branch (AGB) and post-AGB stars from the literature, finding that some PPNe have polarization curves similar to those observed along SNe Ia sight lines. Those polarization curves are produced by scattering on circumstellar dust. We discuss the similarity and the possibility that at least some SNe Ia might explode during the post-AGB phase of their binary companion. Furthermore, we speculate that the peculiar SNe Ia polarization curves might provide observational support to the core-degenerate progenitor model.
Recent high angular resolution observations of protoplanetary disks at different wavelengths have reveled several kind of structures, including multiple bright and dark rings. Embedded planets are the most used explanation for such structures, but there are alternative models capable to shape the dust in rings as it has been observed. We assume a disk around a Herbig star and investigate the effect that ice lines have on the dust evolution, following the growth, fragmentation and dynamics of multiple dust size particles, covering from 1 $\mu$m to 2 m sized objects. We use simplified prescriptions of the fragmentation velocity threshold, which is assumed to change radially at the location of one, two, or three ice lines. We assume changes at the radial location of main volatiles, specifically H$_2$O, CO$_2$, and NH$_3$. Radiative transfer calculations are done using the resulting dust density distributions in order to compare with current multi-wavelength observations. We find that the structures in the dust density profiles and radial intensities at different wavelengths strongly depend on the disk viscosity. A clear gap of emission can be formed between ice lines and be surrounded by ring-like structures, in particular between the H$_2$O and CO$_2$ (or CO). The gaps are expected to be shallower and narrower at millimeter emission than at near-infrared, opposite to model predictions of particle trapping. In our models, the total gas surface density is not expected to show strong variations, in contrast to other gap-forming scenarios such as embedded giant planets or radial variations of the disk viscosity.
A recent study reported a strong apparent depression of Fe I, relative to Fe II, in the AGB stars of NGC 6752. This depression is much greater than that expected from the neglect of non-local thermodynamic equilibrium effects, in particular the dominant effect of overionisation. Here we attempt to reproduce the apparent Fe discrepancy, and investigate differences in reported sodium abundances. We compare in detail the methods and results of the recent study with those of an earlier study of NGC 6752 AGB stars. Iron and sodium abundances are derived using Fe I, Fe II, and Na I lines. Various uncertainties are explored. We reproduce the large Fe I depression found by the recent study, using different observational data and computational tools. Further investigation shows that the degree of the apparent Fe I depression is strongly dependent on the adopted stellar effective temperature. To minimise uncertainties in Fe I we derive temperatures for each star individually using the infrared flux method (IRFM). We find that the $T_{\rm{eff}}$ scales used by both the previous studies are cooler, by up to 100 K; such underestimated temperatures amplify the apparent Fe I depression. Our IRFM temperatures result in negligible apparent depression, consistent with theory. We also re-derived sodium abundances and, remarkably, found them to be unaffected by the new temperature scale. [Na/H] in the AGB stars is consistent between all studies. Since Fe is constant, it follows that [Na/Fe] is also consistent between studies, apart from any systematic offsets in Fe. We recommend the use of $(V-K)$ relations for AGB stars. We plan to investigate the effect of the improved temperature scale on other elements, and re-evaluate the subpopulation distributions on the AGB, in the next paper of this series. [abridged]
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We examine the rest-frame ultra-violet (UV) properties of 10 [CII]$\lambda158\,{\rm \mu m}$$-$detected galaxies at $z\sim5.5$ in COSMOS using new HST/WFC3 near-infrared imaging. Together with pre-existing $158\,{\rm \mu m}-$continuum and [CII] line measurements by ALMA, we study their dust attenuation properties on the IRX-$\beta$ diagram, which connects the total dust emission ($\propto$ IRX=log($L_{FIR}/L_{1600}$)) to the line-of-sight dust column ($\propto\beta$). We find systematically bluer UV continuum spectral slopes ($\beta$) compared to previous low-resolution ground-based measurements, which relieves some of the tension between models of dust attenuation and observations at high redshifts. While most of the galaxies are consistent with local starburst or Small Magellanic cloud like dust properties, we find galaxies with low IRX values and a large range in $\beta$ that cannot be explained by models of a uniform dust distribution well mixed with stars. A stacking analysis of Keck/DEIMOS optical spectra indicates that these galaxies are metal-poor with young stellar populations which could significantly alter their spatial dust distribution.
Low mass galaxy cluster systems and groups play an essential role in upcoming cosmological studies such as those to be carried out with eROSITA. Though the effects of active galactic nuclei (AGNs) and merging processes are of special importance to quantify biases like selection effects or deviations from hydrostatic equilibrium, they are poorly understood on the galaxy group scale. We present an analysis of recent deep Chandra and XMM-Newton integrations of NGC741, which provides an excellent example of a group with multiple concurrent phenomena: both an old central radio galaxy and a spectacular infalling head-tail source, strongly-bent jets, a 100kpc radio trail, intriguing narrow X-ray filaments, and gas sloshing features. Supported principally by X-ray and radio continuum data, we address the merging history of the group, the nature of the X-ray filaments, the extent of gas stripping from NGC742, the character of cavities in the group, and the roles of the central AGN and infalling galaxy in heating the intra-group medium.
We describe the sample design for the SDSS-IV MaNGA survey and present the final properties of the main samples along with important considerations for using these samples for science. Our target selection criteria were developed while simultaneously optimizing the size distribution of the MaNGA integral field units (IFUs), the IFU allocation strategy, and the target density to produce a survey defined in terms of maximizing S/N, spatial resolution, and sample size. Our selection strategy makes use of redshift limits that only depend on i-band absolute magnitude ($M_i$), or, for a small subset of our sample, $M_i$ and color (NUV-i). Such a strategy ensures that all galaxies span the same range in angular size irrespective of luminosity and are therefore covered evenly by the adopted range of IFU sizes. We define three samples: the Primary and Secondary samples are selected to have a flat number density with respect to $M_i$ and are targeted to have spectroscopic coverage to 1.5 and 2.5 effective radii (Re), respectively. The Color-Enhanced supplement increases the number of galaxies in the low-density regions of color-magnitude space by extending the redshift limits of the Primary sample in the appropriate color bins. The samples cover the stellar mass range $5\times10^8 \leq M_* \leq 3\times10^{11} M_{\odot}$ and are sampled at median physical resolutions of 1.37 kpc and 2.5 kpc for the Primary and Secondary samples respectively. We provide weights that will statistically correct for our luminosity and color-dependent selection function and IFU allocation strategy, thus correcting the observed sample to a volume limited sample.
Approximately 10 per cent of star clusters are found in pairs, known as binary clusters. We propose a mechanism for binary cluster formation; we use N-body simulations to show that velocity substructure in a single (even fairly smooth) region can cause binary clusters to form. This process is highly stochastic and it is not obvious from a region's initial conditions whether a binary will form and, if it does, which stars will end up in which cluster. We find the probability that a region will divide is mainly determined by its virial ratio, and a virial ratio above 'equilibrium' is generally necessary for binary formation. We also find that the mass ratio of the two clusters is strongly influenced by the initial degree of spatial substructure in the region.
We investigate quasar outflows at $z \geq 6$ by performing zoom-in cosmological hydrodynamical simulations. By employing the SPH code GADGET-3, we zoom in the $2 R_{200}$ region around a $2 \times 10^{12} M_{\odot}$ halo at $z = 6$, inside a $(500 ~ {\rm Mpc})^3$ comoving volume. We compare the results of our AGN runs with a control simulation in which only stellar/SN feedback is considered. Seeding $10^5 M_{\odot}$ BHs at the centers of $10^{9} M_{\odot}$ halos, we find the following results. BHs accrete gas at the Eddington rate over $z = 9 - 6$. At $z = 6$, our most-massive BH has grown to $M_{\rm BH} = 4 \times 10^9 M_{\odot}$. Fast ($v_{r} > 1000$ km/s), powerful ($\dot{M}_{\rm out} \sim 2000 M_{\odot}$/yr) outflows of shock-heated low-density gas form at $z \sim 7$, and propagate up to hundreds kpc. Star-formation is quenched over $z = 8 - 6$, and the total SFR (SFR surface density near the galaxy center) is reduced by a factor of $5$ ($1000$). We analyse the relative contribution of multiple physical process: (i) disrupting cosmic filamentary cold gas inflows, (ii) reducing central gas density, (iii) ejecting gas outside the galaxy; and find that AGN feedback has the following effects at $z = 6$. The inflowing gas mass fraction is reduced by $\sim 12 \%$, the high-density gas fraction is lowered by $\sim 13 \%$, and $\sim 20 \%$ of the gas outflows at a speed larger than the escape velocity ($500$ km/s). We conclude that quasar-host galaxies at $z \geq 6$ are accreting non-negligible amount of cosmic gas, nevertheless AGN feedback quenches their star formation dominantly by powerful outflows ejecting gas out of the host galaxy halo.
We present new Atacama Large Millimeter/submillimeter Array (ALMA) observations of the dust continuum and [C II] 158 $\mu$m fine structure line emission towards a far-infrared-luminous quasar, ULAS J131911.29$+$095051.4 at $z=6.13$, and combine the new Cycle 1 data with ALMA Cycle 0 data. The combined data have an angular resolution $\sim$ $0.3$, and resolve both the dust continuum and the [C II] line emission on few kpc scales. The [C II] line emission is more irregular than the dust continuum emission which suggests different distributions between the dust and [C II]-emitting gas. The combined data confirm the [C II] velocity gradient that we previously detected in lower resolution ALMA image from Cycle 0 data alone. We apply a tilted ring model to the [C II] velocity map to obtain a rotation curve, and constrain the circular velocity to be 427 $\pm$ 55 km s$^{-1}$ at a radius of 3.2 kpc with an inclination angle of 34$^\circ$. We measure the dynamical mass within the 3.2 kpc region to be 13.4$_{-5.3}^{+7.8}$ $\times 10^{10}\,M_{\odot}$. This yields a black hole and host galaxy mass ratio of 0.020$_{-0.007}^{+0.013}$, which is about 4$_{-2}^{+3}$ times higher than the present-day $M_{\rm BH}$/$M_{\rm bulge}$ ratio. This suggests that the supermassive black hole grows the bulk of its mass before the formation of the most of stellar mass in this quasar host galaxy in the early universe.
We report the peculiar chemical abundance patterns of eleven atypical Milky Way (MW) field red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). These atypical giants exhibit strong Al and N enhancements accompanied by C and Mg depletions, strikingly similar to those observed in the so-called second-generation (SG) stars of globular clusters (GCs). Remarkably, we find low-Mg abundances ([Mg/Fe]$<$0.0) together with strong Al and N overabundances in the majority (5/7) of the metal-rich ([Fe/H]$\gtrsim - 1.0$) sample stars, which is at odds with actual observations of SG stars in Galactic CGs of similar metallicities. This chemical pattern is unique and unprecedented among MW stars, posing urgent questions about its origin. These atypical stars could be former SG stars of dissolved GCs formed with intrinsically lower abundances of Mg and enriched Al (subsequently self-polluted by massive AGB stars) or the result of exotic binary systems. We speculate that the stars Mg-deficiency as well as the orbital properties suggest that they could have an extragalactic origin. This discovery should guide future dedicated spectroscopic searches of atypical stellar chemical patterns in our Galaxy; a fundamental step forward to understand the Galactic formation and evolution.
We investigate spatial variations of turbulent properties in the Small Magellanic Cloud (SMC) by using neutral hydrogen HI observations. With the goal of testing the importance of stellar feedback on HI turbulence, we define central and outer SMC regions based on the star formation rate (SFR) surface density, as well as the HI integrated intensity. We use the structure function and the Velocity Channel Analysis (VCA) to calculate the power-law index (gamma) for both underlying density and velocity fields in these regions. In all cases, our results show essentially no difference in gamma between the central and outer regions. This suggests that HI turbulent properties are surprisingly homogeneous across the SMC when probed at a resolution of 30 pc. Contrary to recent suggestions from numerical simulations, we do not find a significant change in gamma due to stellar feedback as traced by the SFR surface density. This could be due to the stellar feedback being widespread over the whole of the SMC, but more likely due to a large-scale gravitational driving of turbulence. We show that the lack of difference between central and outer SMC regions can not be explained by the high optical depth HI.
Previous radio observations revealed widespread gas-phase methanol (CH$_3$OH) in the Central Molecular Zone (CMZ) at the Galactic center (GC), but its origin remains unclear. Here, we report the discovery of CH$_3$OH ice toward a star in the CMZ, based on a Subaru $3.4$-$4.0\ \mu$m spectrum, aided by NASA/IRTF $L'$ imaging and $2$-$4\ \mu$m spectra. The star lies $\sim8000$ au away in projection from a massive young stellar object (MYSO). Its observed high CH$_3$OH ice abundance ($17\%\pm3\%$ relative to H$_2$O ice) suggests that the $3.535\ \mu$m CH$_3$OH ice absorption likely arises in the MYSO's extended envelope. However, it is also possible that CH$_3$OH ice forms with a higher abundance in dense clouds within the CMZ, compared to within the disk. Either way, our result implies that gas-phase CH$_3$OH in the CMZ can be largely produced by desorption from icy grains. The high solid CH$_3$OH abundance confirms the prominent $15.4\ \mu$m shoulder absorption observed toward GC MYSOs arises from CO$_2$ ice mixed with CH$_3$OH.
PKS 1155+251 is a radio-loud quasar source at z=0.203. Observations using very long baseline interferometry (VLBI) at ~2, 5, 8 and 15 GHz show that the structure of the radio source is quite complicated on parsec scales and that the outer hot spots are apparently undergoing a significant contraction. Because these results cannot be fully explained based on the compact symmetric object (CSO) scenario with a radio core located between the northern and southern complexes, we made observations with the Very Long Baseline Array (VLBA) at 24 and 43 GHz to search for compact substructures and alternative interpretations. The results show that the radio core revealed in the previous VLBI observations remains compact with a flat spectrum in our sub-milli-arcsecond--resolution images; the northern lobe emission becomes faint at 24 GHz and is mostly resolving out at 43 GHz; the southern complex is more bright but has been resolved into the brightest southern-end (S1) and jet or tail alike components westwards. Explaining the southern components aligned westward with a standard CSO scenario alone remains a challenge. As for the flatter spectral index of the southern-end component S1 between 24 and 43 GHz in our observations and the significant 15 GHz VLBA flux variability of S1, an alternative scenario is that the southern complex may be powered by a secondary black hole residing at S1. But more sensitive and high-resolution VLBI monitoring is required to discriminate the CSO and the binary black hole scenarios.
We conduct a comprehensive study of the effects of incorporating galaxy morphology information in photometric redshift estimation. Using machine learning methods, we assess the changes in the scatter and catastrophic outlier fraction of photometric redshifts when galaxy size, ellipticity, S\'{e}rsic index and surface brightness are included in training on galaxy samples from the SDSS and the CFHT Stripe-82 Survey (CS82). We show that by adding galaxy morphological parameters to full $ugriz$ photometry, only mild improvements are obtained, while the gains are substantial in cases where fewer passbands are available. For instance, the combination of $grz$ photometry and morphological parameters almost fully recovers the metrics of $5$-band photometric redshifts. We demonstrate that with morphology it is possible to determine useful redshift distribution $N(z)$ of galaxy samples without any colour information. We also find that the inclusion of quasar redshifts and associated object sizes in training improves the quality of photometric redshift catalogues, compensating for the lack of a good star-galaxy separator. We further show that morphological information can mitigate biases and scatter due to bad photometry. As an application, we derive both point estimates and posterior distributions of redshifts for the official CS82 catalogue, training on morphology and SDSS Stripe-82 $ugriz$ bands when available. Our redshifts yield a 68th percentile error of $0.058(1+z)$, and a catastrophic outlier fraction of $5.2$ per cent. We further include a deep extension trained on morphology and single $i$-band CS82 photometry.
Aims. We study whether rotational excitation makes a difference to the
abundances of the $\rm H_3^+$ isotopologs, including spin states, in physical
conditions corresponding to starless cores and protostellar envelopes.
Methods. We developed a new rate coefficient set for the $\rm H_3^+$
isotopologs, allowing for rotational excitation, using the state-to-state rate
coefficients from Hugo et al. These new so-called species-to-species rate
coefficients are compared with previously-used ground state-to-species rate
coefficients.
Results. The species-to-species and ground state-to-species model results
differ at high density and toward increasing temperatures ($T > 10$ K). The
species-to-species model predicts a lower $\rm H_3^+$ deuteration degree at
high density owing to an increase of the rate coefficients of endothermic
reactions that decrease deuteration. At 20 K the ground state-to-species model
overestimates the abundance of $\rm H_2D^+$ by a factor of about two while the
abundance of $\rm D_3^+$ can differ by an order of magnitude between the
models. Spin-state abundance ratios are also affected, and the new model better
reproduces recent observations of ortho and para $\rm H_2D^+$ and $\rm D_2H^+$.
The applicability regime of the new rate coefficients depends on the critical
densities of the various rotational transitions.
Conclusions. The difference in the abundances of the $\rm H_3^+$ isotopologs
predicted by the two models is negligible at 10 K but excited states are very
important in studies of deuteration at higher temperatures, for example in
protostellar envelopes. The species-to-species rate coefficients provide a more
realistic approach to the chemistry of the $\rm H_3^+$ isotopologs than the
ground state-to-species rate coefficients do, and so the former should be
adopted in chemical models describing the chemistry of the $\rm H_3^+ + H_2$
reacting system.
The mergers of galaxy clusters are the most energetic events in the universe after the Big Bang. With the increased availability of multi-object spectroscopy and X-ray data an ever increasing fraction of local clusters are recognised as exhibiting signs of recent or past merging events on various scales. Our goal is to probe how these mergers affect the evolution and content of their member galaxies. We specifically aim to answer the following questions: Is the quenching of star formation in merging clusters enhanced when compared with relaxed clusters? Is the quenching preceded by a (short lived) burst of star formation? We obtained optical spectroscopy of >400 galaxies in the field of the merging cluster Abell 520. We combine these observations with archival data to get a comprehensive picture of the state of star formation in the members of this merging cluster. Finally, we compare these observations with a control sample of 10 non-merging clusters at the same redshift from The Arizona Cluster Redshift Survey (ACReS). We split the member galaxies in passive, star forming or recently quenched depending on their spectra. The core of the merger shows a decreased fraction of star forming galaxies compared to clusters in the non-merging sample. This region, dominated by passive galaxies, is extended along the axis of the merger. We find evidence of rapid quenching of the galaxies during the core passage with no signs of a star burst on the time scales of the merger (~0.4Gyr). Additionally, we report the tentative discovery of an infalling group along the main filament feeding the merger, currently at ~2.5 Mpc from the merger centre. This group contains a high fraction of star forming galaxies as well as ~2/3 of all the recently quenched galaxies in our survey.
Quasar microlensing analyses implicitly generate a model of the variability of the source quasar. The implied source variability may be unrealistic yet its likelihood is generally not evaluated. We used the damped random walk (DRW) model for quasar variability to evaluate the likelihood of the source variability and applied the revised algorithm to a microlensing analysis of the lensed quasar RX J1131-1231. We compared the estimates of the source quasar disk and average lens galaxy stellar mass with and without applying the DRW likelihoods for the source variability model and found no significant effect on the estimated physical parameters. The most likely explanation is that unreliastic source light curve models are generally associated with poor microlensing fits that already make a negligible contribution to the probability distributions of the derived parameters.
The rate of tidal disruption events (TDEs) is predicted to depend on stellar conditions in the vicinity of the super-massive black hole (SMBH). For most galaxies, the properties of this parsec-scale region cannot be measured directly. Here, we test whether the TDE rate is correlated with global galaxy properties, which are observable. We concentrate on surface stellar mass density ($\Sigma_{M_\star}$) and velocity dispersion ($\sigma_v$), which one would expect to be correlated with the density and velocity dispersion of the stars around the SMBH. We analyze the host galaxies of 33 TDEs and find that at a fixed stellar mass, TDE host galaxies are denser than the background galaxy population. This higher density is significant in comparison with all galaxies, including the subsample of star-forming galaxies. We confirm the earlier claim by Arcavi et al. and French et al. that quiescent galaxies with strong Balmer absorption lines (many of which are post-starburst, aka E+A, galaxies) are overrepresented among TDE hosts. Since these rare galaxies are on average denser than other types of galaxies, their overrepresentation among TDE hosts might arise in part from their shared higher density. Finally, we formulate an empirical relation between the TDE rate, $R_{\rm TDE}$, $\Sigma_{M_\star}$, and $\sigma_v$, as $R_{\rm TDE}\propto \Sigma_{M_\star}^\alpha \times \sigma_v^\beta$, and derive $\hat{\alpha}=0.9\pm0.2$ and $\hat{\beta}=-1.1\pm0.7$. The direct (and significant) dependence on surface stellar mass density and inverse (though not significant) dependence on stellar velocity dispersion support theoretical formulations of the TDE rate that rely on dynamical relaxation of the stars around the SMBH.
Recently, Squire & Hopkins (2017) showed any coupled dust-gas mixture is subject to a class of linear 'resonant drag instabilities' (RDI). These can drive large dust-to-gas ratio fluctuations even at arbitrarily small dust-to-gas mass ratios $\mu$. Here, we explore the RDI in the simple case where the gas satisfies neutral hydrodynamics and supports acoustic waves ($\omega^{2}=c_{s}^{2}\,k^{2}$). The gas and dust are coupled via an arbitrary drag law and subject to external accelerations (e.g. gravity, radiation pressure). If there is any dust drift velocity, the system is unstable. The instabilities exist for all dust-to-gas ratios $\mu$ and their growth rates depend only weakly on $\mu$, as $\sim\mu^{1/3}$. The behavior changes depending on whether the drift velocity is larger or smaller than the sound speed $c_{s}$. In the supersonic limit a 'resonant' instability appears with growth rate increasing without limit with wavenumber, even for vanishingly small $\mu$ and values of the coupling strength ('stopping time'). In the subsonic limit instabilities always exist, but their growth rates no longer increase indefinitely towards small wavelengths. The results are robust to the drag law and equation-of-state of the gas. The instabilities directly drive exponentially growing dust-to-gas-ratio fluctuations, which can be large even when the modes are otherwise weak. We discuss physical implications for cool-star winds, AGN-driven winds and torii, and starburst winds: the instabilities alter the character of these outflows and will drive clumping and turbulence in both gas and dust.
We present a study of simultaneous determination of mean distance and reddening to the Small Magellanic Cloud (SMC) using the two photometric band RR Lyrae data. Currently vailable largest number of highly accurate and precise light curve data of the fundamental mode RR Lyrae stars (RRab) with better areal coverage released by the Optical Gravitational Lensing Experiment (OGLE)-IV project observed in the two photometric bands $(V,I)$ were utilized simultaneously in order to determine true distance and reddening independently for each of the individual RRab stars. Different emipirical and theoretical calibrations leading to the determination of absolute magnitude of RRab stars in the two bands, $V$ and $I$ along with their mean magnitudes were utilized to calculate the apparent distance moduli of each of these RRab stars in these two bands. Decomposing the apparent distance moduli into true distance modulus and reddening in each of these two bands, individual RRab distance and reddening were estimated solving the two apparent distance moduli equations. Modeling the observed distributions of the true distance moduli and reddenings of the SMC RRab stars as Gaussian, the true mean distance modulus and mean reddening value to the SMC were found to be $\mu_{0}=18.930\pm0.165$ mag and $E(B-V)=0.056\pm0.019$ mag, respectively. This corresponds to a distance of $D = 61.237\pm4.544$~kpc to the SMC. The three dimensional distribution of the SMC RRab stars was approximated as ellipsoid. Then using the principal axes transformation method \citep{deb14} we find the axes ratios of the SMC: $1.000\pm0.001$,$1.100\pm 0.001$, $2.600\pm0.015$ with $i=2^{\circ}.300\pm0^{\circ}.140$ and $\theta_{\text{lon}}=38^{\circ}.500\pm0.300$. These results are in agreement with other recent independent previous studies using different tracers and methodologies.
Understanding how young stars and their circumstellar disks form and evolve is key to explain how planets form. The evolution of the star and the disk is regulated by different processes, both internal to the system or related to their environment. The former include accretion of material onto the central star, wind emission, and photoevaporation of the disk due to high-energy radiation from the central star. These are best studied spectroscopically, and the distance to the star is a key parameter in all these studies. Here we present new estimates of the distance to a complex of nearby star-forming clouds obtained combining TGAS distances with measurement of extinction on the line of sight. Furthermore, we show how we plan to study the effects of the environment on the evolution of disks with Gaia, using a kinematic modelling code we have developed to model young star-forming regions.
If the symmetry breaking responsible for axion dark matter production occurs during the radiation-dominated epoch in the early Universe, then this produces large amplitude perturbations that collapse into dense objects known as axion miniclusters. The characteristic minicluster mass, $M_0$, is set by the mass inside the horizon when axion oscillations begin. For the QCD axion $M_0\sim 10^{-10}M_\odot$, however for an axion-like particle $M_0$ can approach $M_\odot$ or higher. Using the Press-Schechter formalism we compute the mass function of halos formed by hierarchical structure formation from these seeds. We compute the concentrations and collapse times of these halos and show that they can grow to be as massive as $10^6M_0$. Within the halos, miniclusters likely remain tightly bound, and we compute their gravitational microlensing signal taking the fraction of axion dark matter collapsed into miniclusters, $f_{\rm MC}$, as a free parameter. A large value of $f_{\rm MC}$ severely weakens constraints on axion scenarios from direct detection experiments. We take into account the non-Gaussian distribution of sizes of miniclusters and determine how this effects the number of microlensing events. We develop the tools to consider microlensing by an extended mass function of non-point-like objects, and use microlensing data to place the first observational constraints on $f_{\rm MC}$. This opens a new window for the potential discovery of the axion.
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We introduce the first two simulations of the IllustrisTNG project, a next generation of cosmological magnetohydrodynamical simulations, focusing on the optical colors of galaxies. We explore TNG100, a rerun of the original Illustris box (~100 Mpc) and TNG300, which includes 2x2500^3 resolution elements in a volume twenty times larger (~300 Mpc); both are run using the new TNG model for galaxy formation. Here we present first results on the galaxy color bimodality at low redshift. Accounting for the attenuation of stellar light by dust, we compare the simulated (g-r) colors of 10^9 < M*/Msun < 10^12.5 galaxies to the observed distribution from the Sloan Digital Sky Survey (SDSS). We find a striking improvement with respect to the original Illustris simulation, as well as excellent quantitative agreement in comparison to the observations, with a sharp transition in median color from blue to red at a characteristic M* ~ 10^10.5 Msun. Investigating the build-up of the color-mass plane and the formation of the red sequence, we demonstrate that the primary driver of galaxy color transition in the TNG model is supermassive blackhole feedback in its low-accretion state. Across the entire population we measure a median color transition timescale dt_green of ~1.6 Gyr, a value which drops for increasingly massive galaxies. We find signatures of the physical process of quenching: at fixed stellar mass, the color of a galaxy correlates with its SFR, age, metallicity, and gas fraction, as well as the magnetic properties of both its interstellar medium and extended gaseous halo. Finally, we measure the amount of stellar mass growth on the red sequence. Galaxies with M* > 10^11 Msun which redden at z<1 accumulate on average ~25% of their final z=0 mass post-reddening; at the same time, ~18% of such massive galaxies acquire half or more of their final stellar mass while on the red sequence.
Hydrodynamical simulations of galaxy formation have now reached sufficient volume to make precision predictions for clustering on cosmologically relevant scales. Here we use our new IllustrisTNG simulations to study the non-linear correlation functions and power spectra of baryons, dark matter, galaxies and haloes over an exceptionally large range of scales. We find that baryonic effects increase the clustering of dark matter on small scales and damp the total matter power spectrum on scales up to k ~ 10 h/Mpc by 20%. The non-linear two-point correlation function of the stellar mass is close to a power-law over a wide range of scales and approximately invariant in time from very high redshift to the present. The two-point correlation function of the simulated galaxies agrees well with SDSS at its mean redshift z ~ 0.1, both as a function of stellar mass and when split according to galaxy colour, apart from a mild excess in the clustering of red galaxies in the stellar mass range 10^9-10^10 Msun/h^2. Given this agreement, the TNG simulations can make valuable theoretical predictions for the clustering bias of different galaxy samples. We find that the clustering length of the galaxy auto-correlation function depends strongly on stellar mass and redshift. Its power-law slope gamma is nearly invariant with stellar mass, but declines from gamma ~ 1.8 at redshift z=0 to gamma ~ 1.6 at redshift z ~ 1, beyond which the slope steepens again. We detect significant scale-dependencies in the bias of different observational tracers of large-scale structure, extending well into the range of the baryonic acoustic oscillations and causing nominal (yet fortunately correctable) shifts of the acoustic peaks of around ~5%.
The distribution of elements in galaxies provides a wealth of information about their production sites and their subsequent mixing into the interstellar medium. Here we investigate the distribution of elements within stars in the IllustrisTNG simulations. In particular, we analyze the abundance ratios of magnesium and europium in Milky Way-like galaxies from the TNG100 simulation (stellar masses ${\log} (M_\star / {\rm M}_\odot) \sim 9.7 - 11.2$). As abundances of magnesium and europium for individual stars in the Milky Way are observed across a variety of spatial locations and metallicities, comparison with the stellar abundances in our more than $850$ Milky Way-like galaxies provides stringent constraints on our chemical evolutionary methods. To this end we use the magnesium to iron ratio as a proxy for the effects of our SNII and SNIa metal return prescription, and a means to compare our simulated abundances to a wide variety of galactic observations. The europium to iron ratio tracks the rare ejecta from neutron star -- neutron star mergers, the assumed primary site of europium production in our models, which in turn is a sensitive probe of the effects of metal diffusion within the gas in our simulations. We find that europium abundances in Milky Way-like galaxies show no correlation with assembly history, present day galactic properties, and average galactic stellar population age. In general, we reproduce the europium to iron spread at low metallicities observed in the Milky Way, with the level of enhancement being sensitive to gas properties during redshifts $z \approx 2-4$. We show that while the overall normalization of [Eu/Fe] is susceptible to resolution and post-processing assumptions, the relatively large spread of [Eu/Fe] at low [Fe/H] when compared to that at high [Fe/H] is very robust.
The fraction of galaxies supported by internal rotation compared to galaxies stabilized by internal pressure provides a strong constraint on galaxy formation models. In integral field spectroscopy surveys, this fraction is biased because survey instruments typically only trace the inner parts of the most massive galaxies. We present aperture corrections for the two most widely used stellar kinematic quantities $V/\sigma$ and $\lambda_{R}$. Our demonstration involves integral field data from the SAMI Galaxy Survey and the ATLAS$^{\rm{3D}}$ Survey. We find a tight relation for both $V/\sigma$ and $\lambda_{R}$ when measured in different apertures that can be used as a linear transformation as a function of radius, i.e., a first-order aperture correction. We find that $V/\sigma$ and $\lambda_{R}$ radial growth curves are well approximated by second order polynomials. By only fitting the inner profile (0.5$R_{\rm{e}}$), we successfully recover the profile out to one $R_{\rm{e}}$ if a constraint between the linear and quadratic parameter in the fit is applied. However, the aperture corrections for $V/\sigma$ and $\lambda_{R}$ derived by extrapolating the profiles perform as well as applying a first-order correction. With our aperture-corrected $\lambda_{R}$ measurements, we find that the fraction of slow rotating galaxies increases with stellar mass. For galaxies with $\log M_{*}/M_{\odot}>$ 11, the fraction of slow rotators is $35.9\pm4.3$ percent, but is underestimated if galaxies without coverage beyond one $R_{\rm{e}}$ are not included in the sample ($24.2\pm5.3$ percent). With measurements out to the largest aperture radius the slow rotator fraction is similar as compared to using aperture corrected values ($38.3\pm4.4$ percent). Thus, aperture effects can significantly bias stellar kinematic IFS studies, but this bias can now be removed with the method outlined here.
The most rapidly evolving regions of galaxies often display complex optical spectra with emission lines excited by massive stars, shocks and accretion onto supermassive black holes. Standard calibrations (such as for the star formation rate) cannot be applied to such mixed spectra. In this paper we isolate the contributions of star formation, shock excitation and active galactic nucleus (AGN) activity to the emission line luminosities of individual spatially resolved regions across the central 3 $\times$ 3 kpc$^2$ region of the active barred spiral galaxy NGC$\sim$613. The star formation rate and AGN luminosity calculated from the decomposed emission line maps are in close agreement with independent estimates from data at other wavelengths. The star formation component traces the B-band stellar continuum emission, and the AGN component forms an ionization cone which is aligned with the nuclear radio jet. The optical line emission associated with shock excitation is cospatial with strong $H_2$ and [Fe II] emission and with regions of high ionized gas velocity dispersion ($\sigma > 100$ km s$^{-1}$). The shock component also traces the outer boundary of the AGN ionization cone and may therefore be produced by outflowing material interacting with the surrounding interstellar medium. Our decomposition method makes it possible to determine the properties of star formation, shock excitation and AGN activity from optical spectra, without contamination from other ionization mechanisms.
The IllustrisTNG project is a new suite of cosmological magneto-hydrodynamical simulations of galaxy formation performed with the moving-mesh code Arepo and updated models for feedback physics. Here we introduce the first two simulations of the series, TNG100 and TNG300, and quantify the stellar mass content of about 4000 massive galaxy groups and clusters ($10^{13} \leq M_{\rm 200c}/M_{\rm sun} \leq 10^{15}$) at recent times ($z \leq 1$). We find that, while Milky Way-sized haloes contain about 95% of their diffuse stars within the inner tenth of their virial radii, this fraction drops to just 50% for the richest galaxy clusters. These clusters have half of their total stellar mass bound to satellite galaxies, with the other half being associated with the central galaxy and the diffuse intra-cluster light (ICL). The exact ICL fraction depends sensitively on the definition of a central galaxy's mass and varies in our most massive clusters between 20 to 40% of the total stellar mass. Haloes of $5\times 10^{14}M_{\rm sun}$ and above have more diffuse stellar mass outside 100 kpc than within 100 kpc, with power-law slopes of the radial density distribution as shallow as the dark matter's ( $-3.5 < \alpha_{\rm 3D} < -3$). We confirm that total halo mass is a very good predictor of stellar mass, and vice versa: the stellar mass measured within 30 kpc scales as $\propto (M_{\rm 500c})^{0.49}$ with a $\sim 0.12$ dex scatter. The 3D stellar half mass radii of massive galaxies fall too on a tight ($\sim$0.16 dex scatter) power-law relation with halo mass, $r^{\rm stars}_{\rm 0.5} \propto (M_{\rm 500c})^{0.53}$. Even more fundamentally, we find that halo mass alone is a good predictor for the whole stellar mass profiles of massive galaxies beyond the inner few kpc, and we show how on average these can be precisely recovered given a single mass measurement of the galaxy or its halo.
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides the opportunity to measure elemental abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze the chemical abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed chemical abundances and the first time C, N, P, K, V, Cr, Co, and Ni have been studied at high-resolution in this galaxy. We find that the Sgr stars with [Fe/H] $\gtrsim$ -0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light IMF, one lacking the most massive stars that would normally pollute the ISM with the hydrostatic elements. We use a simple chemical evolution model, flexCE to further backup our claim and conclude that recent stellar generations of Fornax and the LMC could also have formed according to a top-light IMF.
We study the consistency of the physical properties of galaxies retrieved from SED-fitting as a function of spectral resolution and signal-to-noise ratio (SNR). Using a selection of physically motivated star formation histories, we set up a control sample of mock galaxy spectra representing observations of the local universe in high-resolution spectroscopy, and in 56 narrow-band and 5 broad-band photometry. We fit the SEDs at these spectral resolutions and compute their corresponding the stellar mass, the mass- and luminosity-weighted age and metallicity, and the dust extinction. We study the biases, correlations, and degeneracies affecting the retrieved parameters and explore the r\^ole of the spectral resolution and the SNR in regulating these degeneracies. We find that narrow-band photometry and spectroscopy yield similar trends in the physical properties derived, the former being considerably more precise. Using a galaxy sample from the SDSS, we compare more realistically the results obtained from high-resolution and narrow-band SEDs (synthesized from the same SDSS spectra) following the same spectral fitting procedures. We use results from the literature as a benchmark to our spectroscopic estimates and show that the prior PDFs, commonly adopted in parametric methods, may introduce biases not accounted for in a Bayesian framework. We conclude that narrow-band photometry yields the same trend in the age-metallicity relation in the literature, provided it is affected by the same biases as spectroscopy; albeit the precision achieved with the latter is generally twice as large as with the narrow-band, at SNR values typical of the different kinds of data.
The growth of black holes (BHs) in disk galaxies lacking classical bulges, which implies an absence of significant mergers, appears to be driven by secular processes. Short bars of sub-kiloparsec radius have been hypothesized to be an important mechanism for driving gas inflows to small scale, feeding central BHs. In order to quantify the maximum BH mass allowed by this mechanism, we examine the robustness of short bars to the dynamical influence of BHs. Large-scale bars are expected to be robust, long-lived structures; extremely massive BHs, which are rare, are needed to completely destroy such bars. However, we find that short bars, which are generally embedded in large-scale outer bars, can be destroyed quickly when BHs of mass $M_{\rm bh}\sim0.05-0.2\%$ of the total stellar mass ($M_\star$) are present. In agreement with this prediction, all galaxies observed to host short bars have BHs with a mass fraction less than $0.2\%M_\star$. Thus the dissolution of short inner bars is possible, perhaps even frequent, in the universe. An important implication of this result is that inner bar-driven gas inflows may be terminated when BHs grow to $\sim0.1\%M_\star$. We predict that $0.2\%M_\star$ is the maximum mass of BHs allowed if they are fed predominately via inner bars. This value matches well the maximum ratio of BH-to-host galaxy stellar mass observed in galaxies with pseudo-bulges and most nearby AGN host galaxies. This hypothesis provides a novel explanation for the lower $M_{\rm bh}/M_\star$ in galaxies which have avoided significant mergers compared with galaxies with classical bulges.
Simulations have shown that bars are subject to a vertical buckling instability that transforms thin bars into boxy or peanut-shaped structures, but the physical conditions necessary for buckling to occur are not fully understood. We use the large sample of local disk galaxies in the Carnegie-Irvine Galaxy Survey to examine the incidence of bars and buckled bars across the Hubble sequence. Depending on the disk inclination angle ($i$), a buckled bar reveals itself as either a boxy/peanut-shaped bulge (at high $i$) or as a barlens structure (at low $i$). We visually identify bars, boxy/peanut-shaped bulges, and barlenses, and examine the dependence of bar and buckled bar fractions on host galaxy properties, including Hubble type, stellar mass, color, and gas mass fraction. We find that the barred and unbarred disks show similar distributions in these physical parameters. The bar fraction is higher (70\%--80\%) in late-type disks with low stellar mass ($M_{*} < 10^{10.5}\, M_{\odot}$) and high gas mass ratio. In contrast, the buckled bar fraction increases to 80\% toward massive and early-type disks ($M_{*} > 10^{10.5}\, M_{\odot}$), and decreases with higher gas mass ratio. These results suggest that bars are more difficult to grow in massive disks that are dynamically hotter than low-mass disks. However, once a bar forms, it can easily buckle in the massive disks, where a deeper potential can sustain the vertical resonant orbits. We also find a probable buckling bar candidate (ESO 506$-$G004) that could provide further clues to understand the timescale of the buckling process.
In modern cosmology, determining the Hubble constant (H0) using distance ladder to percent level and comparing with the results from Planck satellite can shed light on the nature of the dark energy, the physics of neutrino, and the curvature of the universe. Thanks to the endeavor of the SH0ES team, the uncertainty of the H0 has be dramatically reduced from 10% to 2.4%, with the promise to reach even 1% in the near future. In this regard, it is fundamentally important to beat and investigate the systematics. This is best be done with other independent good distance indicators. One of the promising method is the flux-weighted gravity luminosity relation (FGLR) of the blue supergiants. As the blue supergiants are the brightest objects in the galaxies, they can probe distance up to 10 Mpc, with negligible blending effects. While the FGLR method delivered distance in good agreement with other distance indicators, it has been shown that this method delivers larger distance in the case of M33 and NGC 55. Here we investigate whether the M33 distance estimate of FGLR suffers systematics from stellar variability. Using CFHT M33 monitoring data, we found 9 out of 22 BSGs showed variability during the course of 500 days, however with amplitudes as small as 0.05 magnitudes. This suggests that stellar variability plays negligible role in the FGLR distance determination.
It has been known for more than thirty years that the distribution of molecular gas in the innermost 300 parsecs of the Milky Way, the Central Molecular Zone, is strongly asymmetric. Indeed, approximately three quarters of molecular emission comes from positive longitudes, and only one quarter from negative longitudes. However, despite much theoretical effort, the origin of this asymmetry has remained a mystery. Here we show that the asymmetry can be neatly explained by unsteady flow of gas in a barred potential. We use high-resolution 3D hydrodynamical simulations coupled to a state-of-the-art chemical network. Despite the initial conditions and the bar potential being completely point-symmetric with respect to the Galactic Centre, asymmetries develop spontaneously as a consequence of thermal and hydrodynamic instabilities. The observed asymmetry must be transient: observations made tens of megayears in the past or in the future would often show an asymmetry in the opposite sense. Fluctuations of amplitude comparable to the observed asymmetry occur for a large fraction of the time in our simulations, and suggest that the present is not an exceptional but rather an ordinary moment in the life of our Galaxy.
In this work we measure and study the cross-correlation signal between a foreground sample of GAMA galaxies with spectroscopic redshifts in the range $0.2<z<0.8$, and a background sample of H-ATLAS galaxies with photometric redshifts $\gtrsim1.2$. It constitutes a substantial improvement over the cross-correlation measurements made by Gonzalez-Nuevo et al. (2014) with updated catalogues and wider area (with $S/N\gtrsim 5$ below 10 arcmins and reaching $S/N\sim 20$ below 30 arcsecs). The better statistics allow us to split the sample in different redshift bins and perform a tomographic analysis (with $S/N\gtrsim 3$ below 10 arcmins and reaching $S/N\sim 15$ below 30 arcsecs). Moreover, we implement a halo model to extract astrophysical information about the background galaxies and the deflectors that are producing the lensing link between the foreground (lenses) and background (sources) samples. In the case of the sources, we find typical masses values in agreement with previous studies: a minimum halo mass to host a central galaxy, $M_{min}\sim 10^{12.23} M_\odot$, and a pivot halo mass to have at least one sub-halo satellite, $M_1\sim 10^{12.85} M_\odot$. However, the lenses are massive galaxies or even galaxy groups/clusters, with minimum mass of $M_{min}\sim 10^{13.06} M_\odot$. Above a mass of $M_1\sim 10^{14.57} M_\odot$ they contain at least one additional satellite galaxy which contributes to the lensing effect. The tomographic analysis shows that, while $M_1$ is almost redshift independent, there is a clear evolution of an increasing $M_{min}$ value with redshift in agreement with theoretical estimations. Finally, the halo modeling allow us to identify a strong lensing contribution to the cross-correlation for angular scales below 30 arcsecs. This interpretation is supported by the results of basic but effective simulations.
We used the Atacama Large (sub-)Millimeter Array (ALMA) and the IRAM Plateau de Bure Interferometer (PdBI) to image, with an angular resolution of 0.5$''$ (120 au) and 1$''$ (235 au), respectively, the emission from 11 different organic molecules in the protostellar binary NGC1333 IRAS 4A. We clearly disentangled A1 and A2, the two protostellar cores present. For the first time, we were able to derive the column densities and fractional abundances simultaneously for the two objects, allowing us to analyse the chemical differences between them. Molecular emission from organic molecules is concentrated exclusively in A2 even though A1 is the strongest continuum emitter. The protostellar core A2 displays typical hot corino abundances and its deconvolved size is 70 au. In contrast, the upper limits we placed on molecular abundances for A1 are extremely low, lying about one order of magnitude below prestellar values. The difference in the amount of organic molecules present in A1 and A2 ranges between one and two orders of magnitude. Our results suggest that the optical depth of dust emission at these wavelengths is unlikely to be sufficiently high to completely hide a hot corino in A1 similar in size to that in A2. Thus, the significant contrast in molecular richness found between the two sources is most probably real. We estimate that the size of a hypothetical hot corino in A1 should be less than 12 au. Our results favour a scenario in which the protostar in A2 is either more massive and/or subject to a higher accretion rate than A1, as a result of inhomogeneous fragmentation of the parental molecular clump. This naturally explains the smaller current envelope mass in A2 with respect to A1 along with its molecular richness.
The offsets between the radial velocities of the rotational transitions of carbon monoxide and the fine structure transitions of neutral and singly ionized carbon are used to test the hypothetical variation of the fine structure constant, alpha. From the analysis of the [CI] and [CII] fine structure lines and low J rotational lines of 12CO and 13CO, emitted by the dark cloud L1599B in the Milky Way disk, we find no evidence for fractional changes in alpha at the level of |$\Delta \alpha/\alpha$| < 3*10^-7. For the neighbour galaxy M33 a stringent limit on Delta alpha/alpha is set from observations of three HII zones in [CII] and CO emission lines: |$\Delta \alpha/\alpha$| < 4*10^-7. Five systems over the redshift interval z = 5.7-6.4, showing CO J=6-5, J=7-6 and [CII] emission, yield a limit on |$\Delta \alpha/\alpha$| < 1.3*10^-5. Thus, a combination of the [CI], [CII], and CO emission lines turns out to be a powerful tool for probing the stability of the fundamental physical constants over a wide range of redshifts not accessible to optical spectral measurements.
We describe new Hi-GAL based maps of the entire Galactic Plane, obtained using continuum data in the wavelength range 70-500 $\mu$m. These maps are derived with the PPMAP procedure, and therefore represent a significant improvement over those obtained with standard analysis techniques. Specifically they have greatly improved resolution (12 arcsec) and, in addition to more accurate integrated column densities and mean dust temperatures, they give temperature-differential column densities, i.e., separate column density maps in twelve distinct dust temperature intervals, along with the corresponding uncertainty maps. The complete set of maps is available on-line. We briefly describe PPMAP and present some illustrative examples of the results. These include (a) multi-temperature maps of the Galactic HII region W5-E, (b) the temperature decomposition of molecular cloud column-density probability distribution functions, and (c) the global variation of mean dust temperature as a function of Galactocentric distance. Amongst our findings are: (i) a strong localised temperature gradient in W5-E in a direction orthogonal to that towards the ionising star, suggesting an alternative heating source and providing possible guidance for models of the formation of the bubble complex, and (ii) the overall radial profile of dust temperature in the Galaxy shows a monotonic decrease, broadly consistent both with models of the interstellar radiation field and with previous estimates at lower resolution. However, we also find a central temperature plateau within ~ 6 kpc of the Galactic centre, outside of which is a pronounced steepening of the radial profile. This behaviour may reflect the greater proportion of molecular (as opposed to atomic) gas in the central region of the Galaxy.
We examine the statistics of the low-redshift Ly-alpha forest in an adaptive mesh refinement hydrodynamic cosmological simulation of sufficient volume to include distinct large-scale environments. We compare our HI column density distribution of absorbers both with recent work and between two highly-refined regions of our simulation: a large-scale overdensity and a large-scale underdensity (on scales of approximately 20 Mpc). We recover the average results presented in Kollmeier et al. (2014) using different simulation methods. We further break down these results as a function of environment to examine the detailed dependence of absorber statistics on large-scale density. We find that the slope of the HI column density distribution in the 10$^{12.5}$ $\le$ N$_{HI}$/cm$^{-2}$ $\le$ 10$^{14.5}$ range depends on environment such that the slope becomes steeper for higher environmental density, and this difference reflects distinct physical conditions of the intergalactic medium on these scales. We track this difference to the different temperature structures of filaments in varying environments. Specifically, filaments in the overdensity are hotter and, correspondingly, are composed of gas with lower HI fractions than those in underdense environments. Our results highlight that in order to understand the physics driving the HI CDD, we need not only improved accounting of the sources of ionizing UV photons, but also of the physical conditions of the IGM and how this may vary as a function of large-scale environment.
We explore the possibility that the gravitational waves (GWs) detected in 2015 were strongly-lensed by massive galaxy clusters. We estimate that the odds on one of the GWs being strongly-lensed is $10^5:1$, taking in to account the binary black hole merger rate, the gravitational optics of known cluster lenses, and the star formation history of the universe. It is therefore very unlikely, but not impossible that one of the GWs was strongly-lensed. We identify three spectroscopically confirmed cluster strong lenses within the 90% credible sky localisations of the three GWs. Moreover, the GW credible regions intersect the disk of the Milky Way, behind which undiscovered strong galaxy cluster lenses may reside. We therefore use well constrained mass models of the three clusters within the credible regions and three further example clusters to predict that half of the putative next appearances of the GWs would be detectable by LIGO, and that they would arrive at Earth within three years of first detection.
We show that a subdominant component of dissipative dark matter resembling the Standard Model can form many intermediate-mass black hole seeds during the first structure formation epoch, such that a few percent of all the dwarf galaxies host one. We also observe that, in the presence of this matter sector, the black holes will grow at a much faster rate with respect to the ordinary case. These facts can explain the observed abundance of supermassive black holes feeding high-redshift quasars. The scenario will have interesting observational consequences, such as dark substructures and gravitational wave production.
Approximately once every $10^4$ years, a star passes close enough to the supermassive black hole Sgr A* at the center of the Milky Way to be pulled apart by the black hole's tidal forces. The star is then "spaghettified" into a long stream of matter, with approximately one half being bound to Sgr A* and the other half unbound. Within this stream, the local self-gravity dominates the tidal field of Sgr A*, which at minimum restricts the stream to a small finite width. As the stream cools from adiabatic expansion and begins to recombine, the residual self-gravity allows for planetary-mass fragments to form along the length of the stream; these fragments are then shot out into the galaxy at range of velocities, with the fastest moving at ~10% c. We determine the phase space distributions of these fragments for a realistic ensemble of stellar disruptions, along with the local density of fragments in the solar neighborhood. We find that ~$10^7$ fragments produced by Sgr A* accumulate within the Milky Way over its lifetime, that there are ~$10^7$ fragments that lie within 1 Mpc of the Milky Way originating from other galaxies, and that the nearest fragment to our Sun is on average 500 pc distant.
The environment around protoplanetary disks (PPDs) regulates processes which
drive the chemical and structural evolution of circumstellar material. We
perform a detailed empirical survey of warm molecular hydrogen (H$_2$)
absorption observed against H I-Ly$\alpha$ (Ly$\alpha$: $\lambda$ 1215.67
{\AA}) emission profiles for 22 PPDs, using archival Hubble Space Telescope
(HST) ultraviolet (UV) spectra from the Cosmic Origins Spectrograph (COS) and
the Space Telescope Imaging Spectrograph (STIS) to identify H$_2$ absorption
signatures and quantify the column densities of H$_2$ ground states in each
sightline. We compare thermal equilibrium models of H$_2$ to the observed H$_2$
rovibrational level distributions. We find that, for the majority of targets,
there is a clear deviation in high energy states (T$_{exc}$ $\gtrsim$ 20,000 K)
away from thermal equilibrium populations (T(H$_2$) $\gtrsim$ 3500 K).
We create a metric to estimate the total column density of non-thermal H$_2$
(N(H$_2$)$_{nLTE}$) and find that the total column densities of thermal
(N(H$_2$)) and N(H$_2$)$_{nLTE}$ correlate for transition disks and targets
with detectable C IV-pumped H$_2$ fluorescence. We compare N(H$_2$) and
N(H$_2$)$_{nLTE}$ to circumstellar observables and find that N(H$_2$)$_{nLTE}$
correlates with X-ray and FUV luminosities, but no correlations are observed
with the luminosities of discrete emission features (e.g., Ly$\alpha$, C IV).
Additionally, N(H$_2$) and N(H$_2$)$_{nLTE}$ are too low to account for the
H$_2$ fluorescence observed in PPDs, so we speculate that this H$_2$ may
instead be associated with a diffuse, hot, atomic halo surrounding the
planet-forming disk. We create a simple photon-pumping model for each target to
test this hypothesis and find that Ly$\alpha$ efficiently pumps H$_2$ levels
with T$_{exc}$ $\geq$ 10,000 K out of thermal equilibrium.
The tidal disruption of a star by a massive black hole is expected to yield a luminous flare of thermal emission. About two dozen of these stellar tidal disruption flares (TDFs) may have been detected in optical transient surveys. However, explaining the observed properties of these events within the tidal disruption paradigm is not yet possible. This theoretical ambiguity has led some authors to suggest that optical TDFs are due to a different process, such as a nuclear supernova or accretion disk instabilities. Here we present a test of a fundamental prediction of the tidal disruption event scenario: a suppression of the flare rate due to the direct capture of stars by the black hole. Using a recently compiled sample of candidate TDFs with black hole mass measurements, plus a careful treatment of selection effects in this flux-limited sample, we confirm that the dearth of observed TDFs from high-mass black holes is statistically significant. All the TDF impostor models we consider fail to explain the observed mass function; the only scenario that fits the data is a suppression of the rate due to direct captures. We find that this suppression can explain the low volumetric rate of the luminous TDF candidate ASASSN-15lh, thus providing new evidence that this flare belongs to the TDF family. Our work is the first to present the optical TDF luminosity function. A steep power-law is required to explain the observed rest-frame g-band luminosity, $dN/dL \propto L^{-2.5}$. Integrating over this power-law yields a mean rate of about $1 \times 10^{-4}$ per galaxy per year, consistent with the theoretically expected tidal disruption rate.
We detect and characterise extended, diffuse radio emission from galaxy clusters at 168 MHz within the Epoch of Reionization 0-hour field; a $45^\circ \times 45^\circ$ region of the southern sky centred on R. A. $= 0^\circ$, decl. $=-27^\circ$. We detect 31 diffuse radio sources; 3 of which are newly detected haloes in Abell 0141, Abell 2811, and Abell S1121; 2 newly detected relics in Abell 0033 and Abell 2751; 5 new halo candidates and a further 5 new relic candidates. Further, we detect a new phoenix candidate in Abell 2556 as well as 2 candidate dead radio galaxies at the centres of Abell 0122 and Abell S1136 likely associated with the brightest cluster galaxies. Beyond this we find 2 clusters with unclassifiable, diffuse steep-spectrum emission as well as a candidate double relic system associated with RXC J2351.0-1934. We present measured source properties such as their integrated flux densities, spectral indices, and sizes where possible. We find several of the diffuse sources to be ultra-steep including the halo in Abell 0141 which has $\alpha \leq -2.1 \pm 0.1$ making it one of the steepest halos known. Finally, we compare our sample of haloes with previously detected haloes and revisit established scaling relations of the radio halo power ($P_{1.4}$) with the cluster X-ray luminosity ($L_{\mathrm{X}}$) and mass ($M_{500}$). We find consistent fitting parameters for assumed power law relationships, and find that the $P_{1.4}-L_{\mathrm{X}}$ has less raw scatter than the corresponding $P_{1.4}-M_{500}$ despite inhomogeneous $L_{\mathrm{X}}$ measurements. These scaling relation properties are consistent with a sample of only non-cool core clusters hosting radio haloes.
We present the near-infrared observations of population II Cepheids in the Galactic bulge from VVV survey. We identify 340 population II Cepheids in the Galactic bulge from VVV survey based on their match with OGLE-III Catalogue. The single-epoch $JH$ and multi-epoch $K_s$ observations complement the accurate periods and optical $(VI)$ mean-magnitudes from OGLE. The sample consisting of BL Herculis and W Virginis subtypes is used to derive period-luminosity relations after correcting mean-magnitudes for the extinction. Our $K_s$-band period-luminosity relation, $K_s = -2.189(0.056)~[\log(P) - 1] + 11.187(0.032)$, is consistent with published work for BL Herculis and W Virginis variables in the Large Magellanic Cloud. We present a combined OGLE-III and VVV catalogue with periods, classification, mean magnitudes and extinction for 264 Galactic bulge population II Cepheids having good-quality $K_s$-band light curves. The absolute magnitudes for population II Cepheids and RR Lyraes calibrated using Gaia and Hubble Space Telescope parallaxes, together with calibrated magnitudes for Large Magellanic Cloud population II Cepheids, are used to obtain a distance to the Galactic center, $R_0=8.34\pm0.03{\mathrm{(stat.)}}\pm0.41{\mathrm{(syst.)}}$, which changes by $^{+ 0.05}_{-0.25}$ with different extinction laws. While noting the limitation of small number statistics, we find that the present sample of population II Cepheids in the Galactic bulge shows a nearly spheroidal spatial distribution, similar to metal-poor RR Lyrae variables. We do not find evidence of the inclined bar as traced by the metal-rich red-clump stars. The number density for population II Cepheids is more limited as compared to abundant RR Lyraes but they are bright and exhibit a wide range in period that provides a robust period-luminosity relation for an accurate estimate of the distance to the Galactic center.
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We introduce the first two simulations of the IllustrisTNG project, a next generation of cosmological magnetohydrodynamical simulations, focusing on the optical colors of galaxies. We explore TNG100, a rerun of the original Illustris box (~100 Mpc) and TNG300, which includes 2x2500^3 resolution elements in a volume twenty times larger (~300 Mpc); both are run using the new TNG model for galaxy formation. Here we present first results on the galaxy color bimodality at low redshift. Accounting for the attenuation of stellar light by dust, we compare the simulated (g-r) colors of 10^9 < M*/Msun < 10^12.5 galaxies to the observed distribution from the Sloan Digital Sky Survey (SDSS). We find a striking improvement with respect to the original Illustris simulation, as well as excellent quantitative agreement in comparison to the observations, with a sharp transition in median color from blue to red at a characteristic M* ~ 10^10.5 Msun. Investigating the build-up of the color-mass plane and the formation of the red sequence, we demonstrate that the primary driver of galaxy color transition in the TNG model is supermassive blackhole feedback in its low-accretion state. Across the entire population we measure a median color transition timescale dt_green of ~1.6 Gyr, a value which drops for increasingly massive galaxies. We find signatures of the physical process of quenching: at fixed stellar mass, the color of a galaxy correlates with its SFR, age, metallicity, and gas fraction, as well as the magnetic properties of both its interstellar medium and extended gaseous halo. Finally, we measure the amount of stellar mass growth on the red sequence. Galaxies with M* > 10^11 Msun which redden at z<1 accumulate on average ~25% of their final z=0 mass post-reddening; at the same time, ~18% of such massive galaxies acquire half or more of their final stellar mass while on the red sequence.
Hydrodynamical simulations of galaxy formation have now reached sufficient volume to make precision predictions for clustering on cosmologically relevant scales. Here we use our new IllustrisTNG simulations to study the non-linear correlation functions and power spectra of baryons, dark matter, galaxies and haloes over an exceptionally large range of scales. We find that baryonic effects increase the clustering of dark matter on small scales and damp the total matter power spectrum on scales up to k ~ 10 h/Mpc by 20%. The non-linear two-point correlation function of the stellar mass is close to a power-law over a wide range of scales and approximately invariant in time from very high redshift to the present. The two-point correlation function of the simulated galaxies agrees well with SDSS at its mean redshift z ~ 0.1, both as a function of stellar mass and when split according to galaxy colour, apart from a mild excess in the clustering of red galaxies in the stellar mass range 10^9-10^10 Msun/h^2. Given this agreement, the TNG simulations can make valuable theoretical predictions for the clustering bias of different galaxy samples. We find that the clustering length of the galaxy auto-correlation function depends strongly on stellar mass and redshift. Its power-law slope gamma is nearly invariant with stellar mass, but declines from gamma ~ 1.8 at redshift z=0 to gamma ~ 1.6 at redshift z ~ 1, beyond which the slope steepens again. We detect significant scale-dependencies in the bias of different observational tracers of large-scale structure, extending well into the range of the baryonic acoustic oscillations and causing nominal (yet fortunately correctable) shifts of the acoustic peaks of around ~5%.
The distribution of elements in galaxies provides a wealth of information about their production sites and their subsequent mixing into the interstellar medium. Here we investigate the distribution of elements within stars in the IllustrisTNG simulations. In particular, we analyze the abundance ratios of magnesium and europium in Milky Way-like galaxies from the TNG100 simulation (stellar masses ${\log} (M_\star / {\rm M}_\odot) \sim 9.7 - 11.2$). As abundances of magnesium and europium for individual stars in the Milky Way are observed across a variety of spatial locations and metallicities, comparison with the stellar abundances in our more than $850$ Milky Way-like galaxies provides stringent constraints on our chemical evolutionary methods. To this end we use the magnesium to iron ratio as a proxy for the effects of our SNII and SNIa metal return prescription, and a means to compare our simulated abundances to a wide variety of galactic observations. The europium to iron ratio tracks the rare ejecta from neutron star -- neutron star mergers, the assumed primary site of europium production in our models, which in turn is a sensitive probe of the effects of metal diffusion within the gas in our simulations. We find that europium abundances in Milky Way-like galaxies show no correlation with assembly history, present day galactic properties, and average galactic stellar population age. In general, we reproduce the europium to iron spread at low metallicities observed in the Milky Way, with the level of enhancement being sensitive to gas properties during redshifts $z \approx 2-4$. We show that while the overall normalization of [Eu/Fe] is susceptible to resolution and post-processing assumptions, the relatively large spread of [Eu/Fe] at low [Fe/H] when compared to that at high [Fe/H] is very robust.
The fraction of galaxies supported by internal rotation compared to galaxies stabilized by internal pressure provides a strong constraint on galaxy formation models. In integral field spectroscopy surveys, this fraction is biased because survey instruments typically only trace the inner parts of the most massive galaxies. We present aperture corrections for the two most widely used stellar kinematic quantities $V/\sigma$ and $\lambda_{R}$. Our demonstration involves integral field data from the SAMI Galaxy Survey and the ATLAS$^{\rm{3D}}$ Survey. We find a tight relation for both $V/\sigma$ and $\lambda_{R}$ when measured in different apertures that can be used as a linear transformation as a function of radius, i.e., a first-order aperture correction. We find that $V/\sigma$ and $\lambda_{R}$ radial growth curves are well approximated by second order polynomials. By only fitting the inner profile (0.5$R_{\rm{e}}$), we successfully recover the profile out to one $R_{\rm{e}}$ if a constraint between the linear and quadratic parameter in the fit is applied. However, the aperture corrections for $V/\sigma$ and $\lambda_{R}$ derived by extrapolating the profiles perform as well as applying a first-order correction. With our aperture-corrected $\lambda_{R}$ measurements, we find that the fraction of slow rotating galaxies increases with stellar mass. For galaxies with $\log M_{*}/M_{\odot}>$ 11, the fraction of slow rotators is $35.9\pm4.3$ percent, but is underestimated if galaxies without coverage beyond one $R_{\rm{e}}$ are not included in the sample ($24.2\pm5.3$ percent). With measurements out to the largest aperture radius the slow rotator fraction is similar as compared to using aperture corrected values ($38.3\pm4.4$ percent). Thus, aperture effects can significantly bias stellar kinematic IFS studies, but this bias can now be removed with the method outlined here.
The most rapidly evolving regions of galaxies often display complex optical spectra with emission lines excited by massive stars, shocks and accretion onto supermassive black holes. Standard calibrations (such as for the star formation rate) cannot be applied to such mixed spectra. In this paper we isolate the contributions of star formation, shock excitation and active galactic nucleus (AGN) activity to the emission line luminosities of individual spatially resolved regions across the central 3 $\times$ 3 kpc$^2$ region of the active barred spiral galaxy NGC$\sim$613. The star formation rate and AGN luminosity calculated from the decomposed emission line maps are in close agreement with independent estimates from data at other wavelengths. The star formation component traces the B-band stellar continuum emission, and the AGN component forms an ionization cone which is aligned with the nuclear radio jet. The optical line emission associated with shock excitation is cospatial with strong $H_2$ and [Fe II] emission and with regions of high ionized gas velocity dispersion ($\sigma > 100$ km s$^{-1}$). The shock component also traces the outer boundary of the AGN ionization cone and may therefore be produced by outflowing material interacting with the surrounding interstellar medium. Our decomposition method makes it possible to determine the properties of star formation, shock excitation and AGN activity from optical spectra, without contamination from other ionization mechanisms.
The IllustrisTNG project is a new suite of cosmological magneto-hydrodynamical simulations of galaxy formation performed with the moving-mesh code Arepo and updated models for feedback physics. Here we introduce the first two simulations of the series, TNG100 and TNG300, and quantify the stellar mass content of about 4000 massive galaxy groups and clusters ($10^{13} \leq M_{\rm 200c}/M_{\rm sun} \leq 10^{15}$) at recent times ($z \leq 1$). We find that, while Milky Way-sized haloes contain about 95% of their diffuse stars within the inner tenth of their virial radii, this fraction drops to just 50% for the richest galaxy clusters. These clusters have half of their total stellar mass bound to satellite galaxies, with the other half being associated with the central galaxy and the diffuse intra-cluster light (ICL). The exact ICL fraction depends sensitively on the definition of a central galaxy's mass and varies in our most massive clusters between 20 to 40% of the total stellar mass. Haloes of $5\times 10^{14}M_{\rm sun}$ and above have more diffuse stellar mass outside 100 kpc than within 100 kpc, with power-law slopes of the radial density distribution as shallow as the dark matter's ( $-3.5 < \alpha_{\rm 3D} < -3$). We confirm that total halo mass is a very good predictor of stellar mass, and vice versa: the stellar mass measured within 30 kpc scales as $\propto (M_{\rm 500c})^{0.49}$ with a $\sim 0.12$ dex scatter. The 3D stellar half mass radii of massive galaxies fall too on a tight ($\sim$0.16 dex scatter) power-law relation with halo mass, $r^{\rm stars}_{\rm 0.5} \propto (M_{\rm 500c})^{0.53}$. Even more fundamentally, we find that halo mass alone is a good predictor for the whole stellar mass profiles of massive galaxies beyond the inner few kpc, and we show how on average these can be precisely recovered given a single mass measurement of the galaxy or its halo.
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides the opportunity to measure elemental abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze the chemical abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed chemical abundances and the first time C, N, P, K, V, Cr, Co, and Ni have been studied at high-resolution in this galaxy. We find that the Sgr stars with [Fe/H] $\gtrsim$ -0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light IMF, one lacking the most massive stars that would normally pollute the ISM with the hydrostatic elements. We use a simple chemical evolution model, flexCE to further backup our claim and conclude that recent stellar generations of Fornax and the LMC could also have formed according to a top-light IMF.
We study the consistency of the physical properties of galaxies retrieved from SED-fitting as a function of spectral resolution and signal-to-noise ratio (SNR). Using a selection of physically motivated star formation histories, we set up a control sample of mock galaxy spectra representing observations of the local universe in high-resolution spectroscopy, and in 56 narrow-band and 5 broad-band photometry. We fit the SEDs at these spectral resolutions and compute their corresponding the stellar mass, the mass- and luminosity-weighted age and metallicity, and the dust extinction. We study the biases, correlations, and degeneracies affecting the retrieved parameters and explore the r\^ole of the spectral resolution and the SNR in regulating these degeneracies. We find that narrow-band photometry and spectroscopy yield similar trends in the physical properties derived, the former being considerably more precise. Using a galaxy sample from the SDSS, we compare more realistically the results obtained from high-resolution and narrow-band SEDs (synthesized from the same SDSS spectra) following the same spectral fitting procedures. We use results from the literature as a benchmark to our spectroscopic estimates and show that the prior PDFs, commonly adopted in parametric methods, may introduce biases not accounted for in a Bayesian framework. We conclude that narrow-band photometry yields the same trend in the age-metallicity relation in the literature, provided it is affected by the same biases as spectroscopy; albeit the precision achieved with the latter is generally twice as large as with the narrow-band, at SNR values typical of the different kinds of data.
The growth of black holes (BHs) in disk galaxies lacking classical bulges, which implies an absence of significant mergers, appears to be driven by secular processes. Short bars of sub-kiloparsec radius have been hypothesized to be an important mechanism for driving gas inflows to small scale, feeding central BHs. In order to quantify the maximum BH mass allowed by this mechanism, we examine the robustness of short bars to the dynamical influence of BHs. Large-scale bars are expected to be robust, long-lived structures; extremely massive BHs, which are rare, are needed to completely destroy such bars. However, we find that short bars, which are generally embedded in large-scale outer bars, can be destroyed quickly when BHs of mass $M_{\rm bh}\sim0.05-0.2\%$ of the total stellar mass ($M_\star$) are present. In agreement with this prediction, all galaxies observed to host short bars have BHs with a mass fraction less than $0.2\%M_\star$. Thus the dissolution of short inner bars is possible, perhaps even frequent, in the universe. An important implication of this result is that inner bar-driven gas inflows may be terminated when BHs grow to $\sim0.1\%M_\star$. We predict that $0.2\%M_\star$ is the maximum mass of BHs allowed if they are fed predominately via inner bars. This value matches well the maximum ratio of BH-to-host galaxy stellar mass observed in galaxies with pseudo-bulges and most nearby AGN host galaxies. This hypothesis provides a novel explanation for the lower $M_{\rm bh}/M_\star$ in galaxies which have avoided significant mergers compared with galaxies with classical bulges.
Simulations have shown that bars are subject to a vertical buckling instability that transforms thin bars into boxy or peanut-shaped structures, but the physical conditions necessary for buckling to occur are not fully understood. We use the large sample of local disk galaxies in the Carnegie-Irvine Galaxy Survey to examine the incidence of bars and buckled bars across the Hubble sequence. Depending on the disk inclination angle ($i$), a buckled bar reveals itself as either a boxy/peanut-shaped bulge (at high $i$) or as a barlens structure (at low $i$). We visually identify bars, boxy/peanut-shaped bulges, and barlenses, and examine the dependence of bar and buckled bar fractions on host galaxy properties, including Hubble type, stellar mass, color, and gas mass fraction. We find that the barred and unbarred disks show similar distributions in these physical parameters. The bar fraction is higher (70\%--80\%) in late-type disks with low stellar mass ($M_{*} < 10^{10.5}\, M_{\odot}$) and high gas mass ratio. In contrast, the buckled bar fraction increases to 80\% toward massive and early-type disks ($M_{*} > 10^{10.5}\, M_{\odot}$), and decreases with higher gas mass ratio. These results suggest that bars are more difficult to grow in massive disks that are dynamically hotter than low-mass disks. However, once a bar forms, it can easily buckle in the massive disks, where a deeper potential can sustain the vertical resonant orbits. We also find a probable buckling bar candidate (ESO 506$-$G004) that could provide further clues to understand the timescale of the buckling process.
In modern cosmology, determining the Hubble constant (H0) using distance ladder to percent level and comparing with the results from Planck satellite can shed light on the nature of the dark energy, the physics of neutrino, and the curvature of the universe. Thanks to the endeavor of the SH0ES team, the uncertainty of the H0 has be dramatically reduced from 10% to 2.4%, with the promise to reach even 1% in the near future. In this regard, it is fundamentally important to beat and investigate the systematics. This is best be done with other independent good distance indicators. One of the promising method is the flux-weighted gravity luminosity relation (FGLR) of the blue supergiants. As the blue supergiants are the brightest objects in the galaxies, they can probe distance up to 10 Mpc, with negligible blending effects. While the FGLR method delivered distance in good agreement with other distance indicators, it has been shown that this method delivers larger distance in the case of M33 and NGC 55. Here we investigate whether the M33 distance estimate of FGLR suffers systematics from stellar variability. Using CFHT M33 monitoring data, we found 9 out of 22 BSGs showed variability during the course of 500 days, however with amplitudes as small as 0.05 magnitudes. This suggests that stellar variability plays negligible role in the FGLR distance determination.
It has been known for more than thirty years that the distribution of molecular gas in the innermost 300 parsecs of the Milky Way, the Central Molecular Zone, is strongly asymmetric. Indeed, approximately three quarters of molecular emission comes from positive longitudes, and only one quarter from negative longitudes. However, despite much theoretical effort, the origin of this asymmetry has remained a mystery. Here we show that the asymmetry can be neatly explained by unsteady flow of gas in a barred potential. We use high-resolution 3D hydrodynamical simulations coupled to a state-of-the-art chemical network. Despite the initial conditions and the bar potential being completely point-symmetric with respect to the Galactic Centre, asymmetries develop spontaneously as a consequence of thermal and hydrodynamic instabilities. The observed asymmetry must be transient: observations made tens of megayears in the past or in the future would often show an asymmetry in the opposite sense. Fluctuations of amplitude comparable to the observed asymmetry occur for a large fraction of the time in our simulations, and suggest that the present is not an exceptional but rather an ordinary moment in the life of our Galaxy.
In this work we measure and study the cross-correlation signal between a foreground sample of GAMA galaxies with spectroscopic redshifts in the range $0.2<z<0.8$, and a background sample of H-ATLAS galaxies with photometric redshifts $\gtrsim1.2$. It constitutes a substantial improvement over the cross-correlation measurements made by Gonzalez-Nuevo et al. (2014) with updated catalogues and wider area (with $S/N\gtrsim 5$ below 10 arcmins and reaching $S/N\sim 20$ below 30 arcsecs). The better statistics allow us to split the sample in different redshift bins and perform a tomographic analysis (with $S/N\gtrsim 3$ below 10 arcmins and reaching $S/N\sim 15$ below 30 arcsecs). Moreover, we implement a halo model to extract astrophysical information about the background galaxies and the deflectors that are producing the lensing link between the foreground (lenses) and background (sources) samples. In the case of the sources, we find typical masses values in agreement with previous studies: a minimum halo mass to host a central galaxy, $M_{min}\sim 10^{12.23} M_\odot$, and a pivot halo mass to have at least one sub-halo satellite, $M_1\sim 10^{12.85} M_\odot$. However, the lenses are massive galaxies or even galaxy groups/clusters, with minimum mass of $M_{min}\sim 10^{13.06} M_\odot$. Above a mass of $M_1\sim 10^{14.57} M_\odot$ they contain at least one additional satellite galaxy which contributes to the lensing effect. The tomographic analysis shows that, while $M_1$ is almost redshift independent, there is a clear evolution of an increasing $M_{min}$ value with redshift in agreement with theoretical estimations. Finally, the halo modeling allow us to identify a strong lensing contribution to the cross-correlation for angular scales below 30 arcsecs. This interpretation is supported by the results of basic but effective simulations.
We used the Atacama Large (sub-)Millimeter Array (ALMA) and the IRAM Plateau de Bure Interferometer (PdBI) to image, with an angular resolution of 0.5$''$ (120 au) and 1$''$ (235 au), respectively, the emission from 11 different organic molecules in the protostellar binary NGC1333 IRAS 4A. We clearly disentangled A1 and A2, the two protostellar cores present. For the first time, we were able to derive the column densities and fractional abundances simultaneously for the two objects, allowing us to analyse the chemical differences between them. Molecular emission from organic molecules is concentrated exclusively in A2 even though A1 is the strongest continuum emitter. The protostellar core A2 displays typical hot corino abundances and its deconvolved size is 70 au. In contrast, the upper limits we placed on molecular abundances for A1 are extremely low, lying about one order of magnitude below prestellar values. The difference in the amount of organic molecules present in A1 and A2 ranges between one and two orders of magnitude. Our results suggest that the optical depth of dust emission at these wavelengths is unlikely to be sufficiently high to completely hide a hot corino in A1 similar in size to that in A2. Thus, the significant contrast in molecular richness found between the two sources is most probably real. We estimate that the size of a hypothetical hot corino in A1 should be less than 12 au. Our results favour a scenario in which the protostar in A2 is either more massive and/or subject to a higher accretion rate than A1, as a result of inhomogeneous fragmentation of the parental molecular clump. This naturally explains the smaller current envelope mass in A2 with respect to A1 along with its molecular richness.
The offsets between the radial velocities of the rotational transitions of carbon monoxide and the fine structure transitions of neutral and singly ionized carbon are used to test the hypothetical variation of the fine structure constant, alpha. From the analysis of the [CI] and [CII] fine structure lines and low J rotational lines of 12CO and 13CO, emitted by the dark cloud L1599B in the Milky Way disk, we find no evidence for fractional changes in alpha at the level of |$\Delta \alpha/\alpha$| < 3*10^-7. For the neighbour galaxy M33 a stringent limit on Delta alpha/alpha is set from observations of three HII zones in [CII] and CO emission lines: |$\Delta \alpha/\alpha$| < 4*10^-7. Five systems over the redshift interval z = 5.7-6.4, showing CO J=6-5, J=7-6 and [CII] emission, yield a limit on |$\Delta \alpha/\alpha$| < 1.3*10^-5. Thus, a combination of the [CI], [CII], and CO emission lines turns out to be a powerful tool for probing the stability of the fundamental physical constants over a wide range of redshifts not accessible to optical spectral measurements.
We describe new Hi-GAL based maps of the entire Galactic Plane, obtained using continuum data in the wavelength range 70-500 $\mu$m. These maps are derived with the PPMAP procedure, and therefore represent a significant improvement over those obtained with standard analysis techniques. Specifically they have greatly improved resolution (12 arcsec) and, in addition to more accurate integrated column densities and mean dust temperatures, they give temperature-differential column densities, i.e., separate column density maps in twelve distinct dust temperature intervals, along with the corresponding uncertainty maps. The complete set of maps is available on-line. We briefly describe PPMAP and present some illustrative examples of the results. These include (a) multi-temperature maps of the Galactic HII region W5-E, (b) the temperature decomposition of molecular cloud column-density probability distribution functions, and (c) the global variation of mean dust temperature as a function of Galactocentric distance. Amongst our findings are: (i) a strong localised temperature gradient in W5-E in a direction orthogonal to that towards the ionising star, suggesting an alternative heating source and providing possible guidance for models of the formation of the bubble complex, and (ii) the overall radial profile of dust temperature in the Galaxy shows a monotonic decrease, broadly consistent both with models of the interstellar radiation field and with previous estimates at lower resolution. However, we also find a central temperature plateau within ~ 6 kpc of the Galactic centre, outside of which is a pronounced steepening of the radial profile. This behaviour may reflect the greater proportion of molecular (as opposed to atomic) gas in the central region of the Galaxy.
We examine the statistics of the low-redshift Ly-alpha forest in an adaptive mesh refinement hydrodynamic cosmological simulation of sufficient volume to include distinct large-scale environments. We compare our HI column density distribution of absorbers both with recent work and between two highly-refined regions of our simulation: a large-scale overdensity and a large-scale underdensity (on scales of approximately 20 Mpc). We recover the average results presented in Kollmeier et al. (2014) using different simulation methods. We further break down these results as a function of environment to examine the detailed dependence of absorber statistics on large-scale density. We find that the slope of the HI column density distribution in the 10$^{12.5}$ $\le$ N$_{HI}$/cm$^{-2}$ $\le$ 10$^{14.5}$ range depends on environment such that the slope becomes steeper for higher environmental density, and this difference reflects distinct physical conditions of the intergalactic medium on these scales. We track this difference to the different temperature structures of filaments in varying environments. Specifically, filaments in the overdensity are hotter and, correspondingly, are composed of gas with lower HI fractions than those in underdense environments. Our results highlight that in order to understand the physics driving the HI CDD, we need not only improved accounting of the sources of ionizing UV photons, but also of the physical conditions of the IGM and how this may vary as a function of large-scale environment.
We explore the possibility that the gravitational waves (GWs) detected in 2015 were strongly-lensed by massive galaxy clusters. We estimate that the odds on one of the GWs being strongly-lensed is $10^5:1$, taking in to account the binary black hole merger rate, the gravitational optics of known cluster lenses, and the star formation history of the universe. It is therefore very unlikely, but not impossible that one of the GWs was strongly-lensed. We identify three spectroscopically confirmed cluster strong lenses within the 90% credible sky localisations of the three GWs. Moreover, the GW credible regions intersect the disk of the Milky Way, behind which undiscovered strong galaxy cluster lenses may reside. We therefore use well constrained mass models of the three clusters within the credible regions and three further example clusters to predict that half of the putative next appearances of the GWs would be detectable by LIGO, and that they would arrive at Earth within three years of first detection.
We show that a subdominant component of dissipative dark matter resembling the Standard Model can form many intermediate-mass black hole seeds during the first structure formation epoch, such that a few percent of all the dwarf galaxies host one. We also observe that, in the presence of this matter sector, the black holes will grow at a much faster rate with respect to the ordinary case. These facts can explain the observed abundance of supermassive black holes feeding high-redshift quasars. The scenario will have interesting observational consequences, such as dark substructures and gravitational wave production.
Approximately once every $10^4$ years, a star passes close enough to the supermassive black hole Sgr A* at the center of the Milky Way to be pulled apart by the black hole's tidal forces. The star is then "spaghettified" into a long stream of matter, with approximately one half being bound to Sgr A* and the other half unbound. Within this stream, the local self-gravity dominates the tidal field of Sgr A*, which at minimum restricts the stream to a small finite width. As the stream cools from adiabatic expansion and begins to recombine, the residual self-gravity allows for planetary-mass fragments to form along the length of the stream; these fragments are then shot out into the galaxy at range of velocities, with the fastest moving at ~10% c. We determine the phase space distributions of these fragments for a realistic ensemble of stellar disruptions, along with the local density of fragments in the solar neighborhood. We find that ~$10^7$ fragments produced by Sgr A* accumulate within the Milky Way over its lifetime, that there are ~$10^7$ fragments that lie within 1 Mpc of the Milky Way originating from other galaxies, and that the nearest fragment to our Sun is on average 500 pc distant.
The environment around protoplanetary disks (PPDs) regulates processes which
drive the chemical and structural evolution of circumstellar material. We
perform a detailed empirical survey of warm molecular hydrogen (H$_2$)
absorption observed against H I-Ly$\alpha$ (Ly$\alpha$: $\lambda$ 1215.67
{\AA}) emission profiles for 22 PPDs, using archival Hubble Space Telescope
(HST) ultraviolet (UV) spectra from the Cosmic Origins Spectrograph (COS) and
the Space Telescope Imaging Spectrograph (STIS) to identify H$_2$ absorption
signatures and quantify the column densities of H$_2$ ground states in each
sightline. We compare thermal equilibrium models of H$_2$ to the observed H$_2$
rovibrational level distributions. We find that, for the majority of targets,
there is a clear deviation in high energy states (T$_{exc}$ $\gtrsim$ 20,000 K)
away from thermal equilibrium populations (T(H$_2$) $\gtrsim$ 3500 K).
We create a metric to estimate the total column density of non-thermal H$_2$
(N(H$_2$)$_{nLTE}$) and find that the total column densities of thermal
(N(H$_2$)) and N(H$_2$)$_{nLTE}$ correlate for transition disks and targets
with detectable C IV-pumped H$_2$ fluorescence. We compare N(H$_2$) and
N(H$_2$)$_{nLTE}$ to circumstellar observables and find that N(H$_2$)$_{nLTE}$
correlates with X-ray and FUV luminosities, but no correlations are observed
with the luminosities of discrete emission features (e.g., Ly$\alpha$, C IV).
Additionally, N(H$_2$) and N(H$_2$)$_{nLTE}$ are too low to account for the
H$_2$ fluorescence observed in PPDs, so we speculate that this H$_2$ may
instead be associated with a diffuse, hot, atomic halo surrounding the
planet-forming disk. We create a simple photon-pumping model for each target to
test this hypothesis and find that Ly$\alpha$ efficiently pumps H$_2$ levels
with T$_{exc}$ $\geq$ 10,000 K out of thermal equilibrium.
The tidal disruption of a star by a massive black hole is expected to yield a luminous flare of thermal emission. About two dozen of these stellar tidal disruption flares (TDFs) may have been detected in optical transient surveys. However, explaining the observed properties of these events within the tidal disruption paradigm is not yet possible. This theoretical ambiguity has led some authors to suggest that optical TDFs are due to a different process, such as a nuclear supernova or accretion disk instabilities. Here we present a test of a fundamental prediction of the tidal disruption event scenario: a suppression of the flare rate due to the direct capture of stars by the black hole. Using a recently compiled sample of candidate TDFs with black hole mass measurements, plus a careful treatment of selection effects in this flux-limited sample, we confirm that the dearth of observed TDFs from high-mass black holes is statistically significant. All the TDF impostor models we consider fail to explain the observed mass function; the only scenario that fits the data is a suppression of the rate due to direct captures. We find that this suppression can explain the low volumetric rate of the luminous TDF candidate ASASSN-15lh, thus providing new evidence that this flare belongs to the TDF family. Our work is the first to present the optical TDF luminosity function. A steep power-law is required to explain the observed rest-frame g-band luminosity, $dN/dL \propto L^{-2.5}$. Integrating over this power-law yields a mean rate of about $1 \times 10^{-4}$ per galaxy per year, consistent with the theoretically expected tidal disruption rate.
We detect and characterise extended, diffuse radio emission from galaxy clusters at 168 MHz within the Epoch of Reionization 0-hour field; a $45^\circ \times 45^\circ$ region of the southern sky centred on R. A. $= 0^\circ$, decl. $=-27^\circ$. We detect 31 diffuse radio sources; 3 of which are newly detected haloes in Abell 0141, Abell 2811, and Abell S1121; 2 newly detected relics in Abell 0033 and Abell 2751; 5 new halo candidates and a further 5 new relic candidates. Further, we detect a new phoenix candidate in Abell 2556 as well as 2 candidate dead radio galaxies at the centres of Abell 0122 and Abell S1136 likely associated with the brightest cluster galaxies. Beyond this we find 2 clusters with unclassifiable, diffuse steep-spectrum emission as well as a candidate double relic system associated with RXC J2351.0-1934. We present measured source properties such as their integrated flux densities, spectral indices, and sizes where possible. We find several of the diffuse sources to be ultra-steep including the halo in Abell 0141 which has $\alpha \leq -2.1 \pm 0.1$ making it one of the steepest halos known. Finally, we compare our sample of haloes with previously detected haloes and revisit established scaling relations of the radio halo power ($P_{1.4}$) with the cluster X-ray luminosity ($L_{\mathrm{X}}$) and mass ($M_{500}$). We find consistent fitting parameters for assumed power law relationships, and find that the $P_{1.4}-L_{\mathrm{X}}$ has less raw scatter than the corresponding $P_{1.4}-M_{500}$ despite inhomogeneous $L_{\mathrm{X}}$ measurements. These scaling relation properties are consistent with a sample of only non-cool core clusters hosting radio haloes.
We present the near-infrared observations of population II Cepheids in the Galactic bulge from VVV survey. We identify 340 population II Cepheids in the Galactic bulge from VVV survey based on their match with OGLE-III Catalogue. The single-epoch $JH$ and multi-epoch $K_s$ observations complement the accurate periods and optical $(VI)$ mean-magnitudes from OGLE. The sample consisting of BL Herculis and W Virginis subtypes is used to derive period-luminosity relations after correcting mean-magnitudes for the extinction. Our $K_s$-band period-luminosity relation, $K_s = -2.189(0.056)~[\log(P) - 1] + 11.187(0.032)$, is consistent with published work for BL Herculis and W Virginis variables in the Large Magellanic Cloud. We present a combined OGLE-III and VVV catalogue with periods, classification, mean magnitudes and extinction for 264 Galactic bulge population II Cepheids having good-quality $K_s$-band light curves. The absolute magnitudes for population II Cepheids and RR Lyraes calibrated using Gaia and Hubble Space Telescope parallaxes, together with calibrated magnitudes for Large Magellanic Cloud population II Cepheids, are used to obtain a distance to the Galactic center, $R_0=8.34\pm0.03{\mathrm{(stat.)}}\pm0.41{\mathrm{(syst.)}}$, which changes by $^{+ 0.05}_{-0.25}$ with different extinction laws. While noting the limitation of small number statistics, we find that the present sample of population II Cepheids in the Galactic bulge shows a nearly spheroidal spatial distribution, similar to metal-poor RR Lyrae variables. We do not find evidence of the inclined bar as traced by the metal-rich red-clump stars. The number density for population II Cepheids is more limited as compared to abundant RR Lyraes but they are bright and exhibit a wide range in period that provides a robust period-luminosity relation for an accurate estimate of the distance to the Galactic center.
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