Search

The scaling of galaxy properties with halo mass suggests that feedback loops regulate star formation, but there is no consensus yet about how those feedback loops work. To help clarify discussions of galaxy-scale feedback, Paper I presented a very simple model for supernova feedback that it called the minimalist regulator model. This followup paper interprets that model and discusses its implications. The model itself is an accounting system that tracks all of the mass and energy associated with a halo's circumgalactic baryons--the central galaxy's atmosphere. Algebraic solutions for the equilibrium states of that model reveal that star formation in low-mass halos self-regulates primarily by expanding the atmospheres of those halos, ultimately resulting in stellar masses that are insensitive to the mass-loading properties of galactic winds. What matters most is the proportion of supernova energy that couples with circumgalactic gas. However, supernova feedback alone fails to expand galactic atmospheres in higher-mass halos. According to the minimalist regulator model, an atmospheric contraction crisis ensues, which may be what triggers strong black-hole feedback. The model also predicts that circumgalactic medium properties emerging from cosmological simulations should depend largely on the specific energy of the outflows they produce, and we interpret the qualitative properties of several numerical simulations in light of that prediction., Comment: 15 pages, 3 figures, Submitted to ApJ

This paper presents a new framework for understanding the relationship between a galaxy and its circumgalactic medium (CGM). It focuses on how imbalances between heating and cooling cause either expansion or contraction of the CGM. It does this by tracking \textit{all} of the mass and energy associated with a halo's baryons, including their gravitational potential energy, even if feedback has pushed some of those baryons beyond the halo's virial radius. We show how a star-forming galaxy's equilibrium state can be algebraically derived within the context of this framework, and we analyze how the equilibrium star formation rate depends on supernova feedback. We consider the consequences of varying the mass loading parameter etaM = Mdot_wind / Mdot_* relating a galaxy's gas mass outflow rate (Mdot_wind) to its star formation rate (Mdot_*) and obtain results that challenge common assumptions. In particular, we find that equilibrium star formation rates in low-mass galaxies are generally insensitive to mass loading, and when mass loading does matter, increasing it actually results in \textit{more} star formation because more supernova energy is needed to resist atmospheric contraction., Comment: 18 pages, 5 figures, submitted to ApJ

Quenching of star formation in the central galaxies of cosmological halos is thought to result from energy released as gas accretes onto a supermassive black hole. The same energy source also appears to lower the central density and raise the cooling time of baryonic atmospheres in massive halos, thereby limiting both star formation and black hole growth, by lifting the baryons in those halos to greater altitudes. One predicted signature of that feedback mechanism is a nearly linear relationship between the central black hole's mass (MBH) and the original binding energy of the halo's baryons. We present the increasingly strong observational evidence supporting a such a relationship, showing that it extends up to halos of mass Mhalo ~10^14 MSun. We then compare current observational constraints on the MBH--Mhalo relation with numerical simulations, finding that black hole masses in IllustrisTNG appear to exceed those constraints at Mhalo < 10^13 MSun and that black hole masses in EAGLE fall short of observations at Mhalo ~ 10^14 MSun. A closer look at IllustrisTNG shows that quenching of star formation and suppression of black hole growth do indeed coincide with black hole energy input that lifts the halo's baryons. However, IllustrisTNG does not reproduce the observed MBH--Mhalo relation because its black holes gain mass primarily through accretion that does not contribute to baryon lifting. We suggest adjustments to some of the parameters in the IllustrisTNG feedback algorithm that may allow the resulting black hole masses to reflect the inherent links between black hole growth, baryon lifting, and star formation among the massive galaxies in those simulations., Comment: 20 pages, 10 figures, Accepted to ApJ (Figures 5 and 6 updated)

Temperature profiles of the hot galaxy cluster intracluster medium (ICM) have a complex non-linear structure that traditional parametric modelling may fail to fully approximate. For this study, we made use of neural networks, for the first time, to construct a data-driven non-parametric model of ICM temperature profiles. A new deconvolution algorithm was then introduced to uncover the true (3D) temperature profiles from the observed projected (2D) temperature profiles. An auto-encoder-inspired neural network was first trained by learning a non-linear interpolatory scheme to build the underlying model of 3D temperature profiles in the radial range of [0.02-2] R$_{500}$, using a sparse set of hydrodynamical simulations from the THREE HUNDRED PROJECT. A deconvolution algorithm using a learning-based regularisation scheme was then developed. The model was tested using high and low resolution input temperature profiles, such as those expected from simulations and observations, respectively. We find that the proposed deconvolution and deprojection algorithm is robust with respect to the quality of the data, the morphology of the cluster, and the deprojection scheme used. The algorithm can recover unbiased 3D radial temperature profiles with a precision of around 5\% over most of the fitting range. We apply the method to the first sample of temperature profiles obtained with XMM{\it -Newton} for the CHEX-MATE project and compared it to parametric deprojection and deconvolution techniques. Our work sets the stage for future studies that focus on the deconvolution of the thermal profiles (temperature, density, pressure) of the ICM and the dark matter profiles in galaxy clusters, using deep learning techniques in conjunction with X-ray, Sunyaev Zel'Dovich (SZ) and optical datasets., Comment: 32 pages, 30 figures, 6 tables, Accepted in A&A

Using $\sim$427 ks of Chandra observations, we present a study of shock heating and ICM cooling in the galaxy cluster RBS 797. We discover three nested pairs of weak shocks at roughly 50 kpc, 80 kpc and 130 kpc from the center. The total energy associated with the shocks is $\sim6\times10^{61}$ erg, with the central AGN driving a pair of weak shocks every 20-30 Myr with a power $P_{sh}\approx10^{46}$ erg s$^{-1}$. Based on its morphology and age ($\sim$30 Myr), the inner cocoon shock is associated with the four equidistant X-ray cavities previously discovered. From the thermodynamic analysis of the inner 30 kpc, we find evidence for ICM condensation into colder gas between and behind the X-ray cavities. The total AGN mechanical power (cavities and shocks) of $3.4\times10^{46}$ erg s$^{-1}$ can balance the ICM radiative losses, estimated as $L_{cool} = 2.3\times10^{45}$ erg s$^{-1}$. By building plots of $P_{cav}$ vs. $L_{cool}$, $P_{shock}$ vs. $L_{cool}$ and $P_{tot}$ vs. $L_{cool}$ for RBS 797 and 14 other galaxy clusters, groups and elliptical galaxies where both cavities and shocks are detected, we verify that the most powerful outbursts are found in the strongest cooling systems. Ultimately, we observe that the mechanical power of the AGN exceeds the gas radiative losses by a factor that is different for FR I and FR II radio galaxies, being less than a few tens for FR Is (as RBS 797) and more than roughly a hundred for FR IIs., Comment: Accepted for publication in ApJ

The origin of the cold gas in central galaxies in groups is still a matter of debate. We present Multi-Unit Spectroscopic Explorer (MUSE) observations of 18 optically selected local Brightest Group Galaxies (BGGs) to study the kinematics and distribution of the optical emission-line gas. MUSE observations reveal a distribution of gas morphologies including ten complex networks of filaments extending up to 10 kpc to two compact (<3 kpc) and five extended (>5 kpc) disk-dominated structures. Some rotating disks show rings and elongated structures arising from the central disk. The kinematics of the stellar component is mainly rotation-dominated, which is very different from the disturbed kinematics and distribution found in the filamentary sources. The ionized gas is kinematically decoupled from the stellar component for most systems, suggesting an external origin for the gas. We also find that the Halpha luminosity correlates with the cold molecular mass. By exploring the thermodynamical properties of the hot atmospheres, we find that the filamentary sources and compact disks are found in systems with small central entropy values and tcool/teddy ratios. This suggests that, like for Brightest Cluster Galaxies in cool core clusters, the ionized gas are likely formed from hot halo gas condensations, consistently with the Chaotic Cold Accretion simulations (as shown via the C-ratio, Tat, and k-plot). We note that gaseous rotating disks are more frequent than in BCGs. An explanation for the origin of the gas in those objects is a contribution to gas fueling by mergers or group satellites, as qualitatively hinted by some sources of the present sample. Nonetheless, we discuss the possibility that some extended disks could also be a transition stage in an evolutionary sequence including filaments, extended disks and compact disks, as described by hot gas condensation models of cooling flows., Comment: 38 pages, and 16 figures. Resubmitted to A&A after referee report

The Voit et al. (2020) black hole feedback valve model predicts relationships between stellar velocity dispersion and atmospheric structure among massive early-type galaxies. In this work, we test that model using the Chandra archival sample of 49 early-type galaxies from Lakhchaura et al. (2018). We consider relationships between stellar velocity dispersion and entropy profile slope, multiphase gas extent, and the ratio of cooling time to freefall time. We also define subsamples based on data quality and entropy profile properties that clarify those relationships and enable more specific tests of the model predictions. We find that the atmospheric properties of early-type galaxies generally align with the predictions of the Voit et al. (2020) model, in that galaxies with greater stellar velocity dispersion tend to have radial profiles of pressure, gas density, and entropy with steeper slopes and less extended multiphase gas. Quantitative agreement with the model predictions improves when the sample is restricted to have low central entropy and stellar velocity dispersion of between 220 and 300 km/s., Comment: Accepted to ApJ, 16 pages, 9 figures

We reveal the importance of ongoing in-situ star formation in the Brightest Cluster Galaxy in the massive cool-core CLASH cluster MACS 1931.8-2635 at z=0.35. Using a multi-wavelength approach, we assess the stellar and warm ionized medium components, spatially resolved by the VLT-MUSE spectroscopy, and link them to the molecular gas by incorporating sub-mm ALMA observations. We measure the fluxes of strong emission lines, allowing us to determine the physical conditions of the warm ionized gas. The ionized gas flux brightness peak corresponds to the location of the supermassive black hole and the system shows a diffuse warm ionized gas tail extending 30 kpc in N-E direction. The ionized and molecular gas are co-spatial and co-moving, with the gaseous component in the tail falling inward, providing fuel for star formation and accretion-powered nuclear activity. The gas is ionized by a mix of star formation and other energetic processes which give rise to LINER-like emission, with active galactic nuclei emission dominant only in the BCG core. We measure a star formation rate of 97 Msun/yr, with its peak at the BCG core. However, star formation accounts for only 50-60% of the energetics needed to ionize the warm gas. In situ star formation generated by thermally unstable intracluster medium cooling and/or dry mergers dominate the stellar mass growth at z<0.5 and these mechanisms account for the build-up of 20% of the mass of the system. Our measurements reveal that the most central regions of the BCG contain the lowest gas phase oxygen abundance, whereas the tail exhibits slightly more elevated values. The galaxy is a dispersion dominated system, typical for massive, elliptical galaxies. The gas and stellar kinematics are decoupled, with the gaseous velocity fields being more closely related to the bulk motions of the intracluster medium., Comment: Accepted for publication in A&A on 26.01.2021; Abstract abridged for arXiv; 31 pages, 20 figures

We use stellar and dynamical mass profiles, combined with a stellar population analysis, of 32 brightest cluster galaxies (BCGs) at redshifts of 0.05 $\leq z \leq$ 0.30, to place constraints on their stellar Initial Mass Function (IMF). We measure the spatially-resolved stellar population properties of the BCGs, and use it to derive their stellar mass-to-light ratios ($\Upsilon_{\star \rm POP}$). We find young stellar populations ($<$200 Myr) in the centres of 22 per cent of the sample, and constant $\Upsilon_{\star \rm POP}$ within 15 kpc for 60 per cent of the sample. We further use the stellar mass-to-light ratio from the dynamical mass profiles of the BCGs ($\Upsilon_{\star \rm DYN}$), modelled using a Multi-Gaussian Expansion (MGE) and Jeans Anisotropic Method (JAM), with the dark matter contribution explicitly constrained from weak gravitational lensing measurements. We directly compare the stellar mass-to-light ratios derived from the two independent methods, $\Upsilon_{\star \rm POP}$ (assuming some IMF) to $\Upsilon_{\star \rm DYN}$ for the subsample of BCGs with no young stellar populations and constant $\Upsilon_{\star \rm POP}$. We find that for the majority of these BCGs, a Salpeter (or even more bottom-heavy) IMF is needed to reconcile the stellar population and dynamical modelling results although for a small number of BCGs, a Kroupa (or even lighter) IMF is preferred. For those BCGs better fit with a Salpeter IMF, we find that the mass-excess factor against velocity dispersion falls on an extrapolation (towards higher masses) of known literature correlations. We conclude that there is substantial scatter in the IMF amongst the highest-mass galaxies., Comment: 15 pages, 11 figures, accepted for publication in MNRAS

The Cluster HEritage project with XMM-Newton - Mass Assembly and Thermodynamics at the Endpoint of structure formation (CHEX-MATE) is a three mega-second Multi-Year Heritage Programme to obtain X-ray observations of a minimally-biased, signal-to-noise limited sample of 118 galaxy clusters detected by Planck through the Sunyaev-Zeldovich effect. The programme, described in detail in this paper, aims to study the ultimate products of structure formation in time and mass. It is composed of a census of the most recent objects to have formed (Tier-1: 0.05 < z < 0.2; 2 x 10e14 M_sun < M_500 < 9 x 10e14 M_sun), together with a sample of the highest-mass objects in the Universe (Tier-2: z < 0.6; M_500 > 7.25 x 10e14 M_sun). The programme will yield an accurate vision of the statistical properties of the underlying population, measure how the gas properties are shaped by collapse into the dark matter halo, uncover the provenance of non-gravitational heating, and resolve the major uncertainties in mass determination that limit the use of clusters for cosmological parameter estimation. We will acquire X-ray exposures of uniform depth, designed to obtain individual mass measurements accurate to 15-20% under the hydrostatic assumption. We present the project motivations, describe the programme definition, and detail the ongoing multi-wavelength observational (lensing, SZ, radio) and theoretical effort that is being deployed in support of the project., Comment: 27 pages, 11 figures; A&A, in press

X-ray emitting atmospheres of non-rotating early-type galaxies and their connection to central active galactic nuclei have been thoroughly studied over the years. However, in systems with significant angular momentum, processes of heating and cooling are likely to proceed differently. We present an analysis of the hot atmospheres of six lenticulars and a spiral galaxy to study the effects of angular momentum on the hot gas properties. We find an alignment between the hot gas and the stellar distribution, with the ellipticity of the X-ray emission generally lower than that of the optical stellar emission, consistent with theoretical predictions for rotationally-supported hot atmospheres. The entropy profiles of NGC 4382 and the massive spiral galaxy NGC 1961 are significantly shallower than the entropy distribution in other galaxies, suggesting the presence of strong heating (via outflows or compressional) in the central regions of these systems. Finally, we investigate the thermal (in)stability of the hot atmospheres via criteria such as the TI- and C-ratio, and discuss the possibility that the discs of cold gas present in these objects have condensed out of the hot atmospheres., Comment: 12 pages, 11 figures, submitted to MNRAS

Star formation in the universe's most massive galaxies proceeds furiously early in time but then nearly ceases. Plenty of hot gas remains available but does not cool and condense into star-forming clouds. Active galactic nuclei (AGN) release enough energy to inhibit cooling of the hot gas, but energetic arguments alone do not explain why quenching of star formation is most effective in high-mass galaxies. In fact, optical observations show that quenching is more closely related to a galaxy's central stellar velocity dispersion ($\sigma_v$) than to any other characteristic. Here, we show that high $\sigma_v$ is critical to quenching because a deep central potential well maximizes the efficacy of AGN feedback. In order to remain quenched, a galaxy must continually sweep out the gas ejected from its aging stars. Supernova heating can accomplish this task as long as the AGN sufficiently reduces the gas pressure of the surrounding circumgalactic medium (CGM). We find that CGM pressure acts as the control knob on a valve that regulates AGN feedback and suggest that feedback power self-adjusts so that it suffices to lift the CGM out of the galaxy's potential well. Supernova heating then drives a galactic outflow that remains homogeneous if $\sigma_v \gtrsim 240 \, {\rm km \, s^{-1}}$. AGN feedback can effectively quench galaxies with a comparable velocity dispersion, but feedback in galaxies with a much lower velocity dispersion tends to result in convective circulation and accumulation of multiphase gas within the galaxy., Comment: 29 pages, 8 figures, published in ApJ

We investigate the stellar and dynamical mass profiles in the centres of 25 brightest cluster galaxies (BCGs) at redshifts of 0.05 $\leq z \leq$ 0.30. Our spectroscopy enables us to robustly measure the Gauss-Hermite higher order velocity moments $h_{3}$ and $h_{4}$, which we compare to measurements for massive early-type galaxies, and central group galaxies. We measure positive central values for $h_{4}$ for all the BCGs. We derive the stellar mass-to-light ratio ($\Upsilon_{\star \rm DYN}$), and velocity anisotropy ($\beta$) based on a Multi-Gaussian Expansion (MGE) and axisymmetric Jeans Anisotropic Methods (JAM, cylindrically- and spherically-aligned). We explicitly include a dark matter halo mass component, which is constrained by weak gravitational lensing measurements for these clusters. We find a strong correlation between anisotropy and velocity dispersion profile slope, with rising velocity dispersion profiles corresponding to tangential anisotropy and decreasing velocity dispersion profiles corresponding to radial anisotropy. The rising velocity dispersion profiles can also indicate a significant contribution from the intracluster light (ICL) to the total light (in projection) in the centre of the galaxy. For a small number of BCGs with rising velocity dispersion profiles, a variable stellar mass-to-light ratio can also account for the profile shape, instead of tangential anisotropy or a significant ICL contribution. We note that, for some BCGs, a variable $\beta_{z}(r)$ (from radial to tangential anisotropy) can improve the model fit to the observed kinematic profiles. The observed diversity in these properties illustrates that BCGs are not the homogeneous class of objects they are often assumed to be., Comment: 25 pages, accepted for publication in MNRAS

We present Atacama Large Millimeter/submillimeter Array observations of the brightest cluster galaxy Hydra-A, a nearby ($z=0.054$) giant elliptical galaxy with powerful and extended radio jets. The observations reveal CO(1-0), CO(2-1), $^{13}$CO(2-1), CN(2-1), SiO(5-4), HCO$^{+}$(1-0), HCO$^{+}$(2-1), HCN(1-0), HCN(2-1), HNC(1-0) and H$_{2}$CO(3-2) absorption lines against the galaxy's bright and compact active galactic nucleus. These absorption features are due to at least 12 individual molecular clouds which lie close to the centre of the galaxy and have velocities of approximately $-50$ to $+10$ km/s relative to its recession velocity, where positive values correspond to inward motion. The absorption profiles are evidence of a clumpy interstellar medium within brightest cluster galaxies composed of clouds with similar column densities, velocity dispersions and excitation temperatures to those found at radii of several kpc in the Milky Way. We also show potential variation in a $\sim 10$ km/s wide section of the absorption profile over a two year timescale, most likely caused by relativistic motions in the hot spots of the continuum source which change the background illumination of the absorbing clouds., Comment: Accepted for publication in MNRAS

To advance our understanding of the fuelling and feedback processes which power the Universe's most massive black holes, we require a significant increase in our knowledge of the molecular gas which exists in their immediate surroundings. However, the behaviour of this gas is poorly understood due to the difficulties associated with observing it directly. We report on a survey of 18 brightest cluster galaxies lying in cool cores, from which we detect molecular gas in the core regions of eight via carbon monoxide (CO), cyanide (CN) and silicon monoxide (SiO) absorption lines. These absorption lines are produced by cold molecular gas clouds which lie along the line of sight to the bright continuum sources at the galaxy centres. As such, they can be used to determine many properties of the molecular gas which may go on to fuel supermassive black hole accretion and AGN feedback mechanisms. The absorption regions detected have velocities ranging from -45 to 283 km s$^{-1}$ relative to the systemic velocity of the galaxy, and have a bias for motion towards the host supermassive black hole. We find that the CN N = 0 - 1 absorption lines are typically 10 times stronger than those of CO J = 0 - 1. This is due to the higher electric dipole moment of the CN molecule, which enhances its absorption strength. In terms of molecular number density CO remains the more prevalent molecule with a ratio of CO/CN $\sim 10$, similar to that of nearby galaxies. Comparison of CO, CN and HI observations for these systems shows many different combinations of these absorption lines being detected., Comment: Accepted for publication in MNRAS

During the last decade, numerous and varied observations, along with increasingly sophisticated numerical simulations, have awakened astronomers to the central role the circumgalactic medium (CGM) plays in regulating galaxy evolution. It contains the majority of the baryonic matter associated with a galaxy, along with most of the metals, and must continually replenish the star forming gas in galaxies that continue to sustain star formation. And while the CGM is complex, containing gas ranging over orders of magnitude in temperature and density, a simple emergent property may be governing its structure and role. Observations increasingly suggest that the ambient CGM pressure cannot exceed the limit at which cold clouds start to condense out and precipitate toward the center of the potential well. If feedback fueled by those clouds then heats the CGM and causes it to expand, the pressure will drop and the "rain" will diminish. Such a feedback loop tends to suspend the CGM at the threshold pressure for precipitation. The coming decade will offer many opportunities to test this potentially fundamental principle of galaxy evolution., Comment: Astro2020 White Paper, 8 pages, 2 figures (differences from Astro2020 version: some typos fixed, some references added)

We present new Karl G. Jansky Very Large Array (VLA, 1.5 GHz) radio data for the giant elliptical galaxy IC 4296, supported by archival radio, X-ray (Chandra, XMM-Newton) and optical (SOAR, HST) observations. The galaxy hosts powerful radio jets piercing through the inner hot X-ray emitting atmosphere, depositing most of the energy into the ambient intra-cluster medium (ICM). Whereas the radio surface brightness of the A configuration image is consistent with a Fanaroff-Riley Class I (FR I) system, the D configuration image shows two bright, relative to the central region, large (~160 kpc diameter), well-defined lobes, previously reported by Killeen et al., at a projected distance r~>230 kpc. The XMM-Newton image reveals an X-ray cavity associated with one of the radio lobes. The total enthalpy of the radio lobes is ~7x10^59 erg and the mechanical power output of the jets is ~10^44 erg/s. The jets are mildly curved and possibly re-brightened by the relative motion of the galaxy and the ICM. The lobes display sharp edges, suggesting the presence of bow shocks, which would indicate that they are expanding supersonically. The central entropy and cooling time of the X-ray gas are unusually low and the nucleus hosts a warm H\alpha+[NII] nebula and a cold molecular CO disk. Because most of the energy of the jets is deposited far from the nucleus, the atmosphere of the galaxy continues to cool, apparently feeding the central supermassive black hole and powering the jet activity., Comment: Accepted for publication in MNRAS

Cosmic gas cycles in and out of galaxies, but outside of galaxies it is difficult to observe except for the absorption lines that circumgalactic clouds leave in the spectra of background quasars. Using photoionization modeling of those lines to determine cloud pressures, we find that galaxies are surrounded by extended atmospheres that confine the clouds and have a radial pressure profile that depends on galaxy mass. Motivated by observations of the universe's most massive galaxies, we compare those pressure measurements with models predicting the critical pressure at which cooler clouds start to precipitate out of the hot atmosphere and rain toward the center. We find excellent agreement, implying that the precipitation limit applies to galaxies over a wide mass range., Comment: Accepted to ApJ Letters (8 pages, 4 figures)

Multi-phase filamentary structures around Brightest Cluster Galaxies are likely a key step of AGN-feedback. We observed molecular gas in 3 cool cluster cores: Centaurus, Abell S1101, and RXJ1539.5 and gathered ALMA and MUSE data for 12 other clusters. Those observations show clumpy, massive and long, 3--25 kpc, molecular filaments, preferentially located around the radio bubbles inflated by the AGN (Active Galactic Nucleus). Two objects show nuclear molecular disks. The optical nebula is certainly tracing the warm envelopes of cold molecular filaments. Surprisingly, the radial profile of the H$\alpha$/CO flux ratio is roughly constant for most of the objects, suggesting that (i) between 1.2 to 7 times more cold gas could be present and (ii) local processes must be responsible for the excitation. Projected velocities are between 100--400 km s$^{-1}$, with disturbed kinematics and sometimes coherent gradients. This is likely due to the mixing in projection of several thin unresolved filaments. The velocity fields may be stirred by turbulence induced by bubbles, jets or merger-induced sloshing. Velocity and dispersions are low, below the escape velocity. Cold clouds should eventually fall back and fuel the AGN. We compare the filament's radial extent, r$_{fil}$, with the region where the X-ray gas can become thermally unstable. The filaments are always inside the low-entropy and short cooling time region, where t$_{cool}$/t$_{ff}$<20 (9 of 13 sources). The range t$_{cool}$/t$_{ff}$, 8-23 at r$_{fil}$, is likely due to (i) a more complex gravitational potential affecting the free-fall time (e.g., sloshing, mergers); (ii) the presence of inhomogeneities or uplifted gas in the ICM, affecting the cooling time. For some of the sources, r$_{fil}$ lies where the ratio of the cooling time to the eddy-turnover time, t$_{cool}$/t$_{eddy}$, is approximately unity., Comment: 33 Pages, 17 Figures, submitted to A&A

Active galactic nuclei play a crucial role in the accretion and ejection of gas in galaxies. Although their outflows are well studied, finding direct evidence of accretion has proved very difficult and has so far been done for very few sources. A promising way to study the significance of cold accretion is by observing the absorption of an active galactic nucleus's extremely bright radio emission by the cold gas lying along the line-of-sight. As such, we present ALMA CO(1-0) and CO(2-1) observations of the Hydra-A brightest cluster galaxy (z=0.054) which reveal the existence of cold, molecular gas clouds along the line-of-sight to the galaxy's extremely bright and compact mm-continuum source. They have apparent motions relative to the central supermassive black hole of between -43 and -4 km s$^{-1}$ and are most likely moving along stable, low ellipticity orbits. The identified clouds form part of a $\sim$$10^{9}$ $\text{M}_{\odot}$, approximately edge-on disc of cold molecular gas. With peak CO(2-1) optical depths of $\tau$=0.88 $^{+0.06}_{-0.06}$, they include the narrowest and by far the deepest absorption of this type which has been observed to date in a brightest cluster galaxy. By comparing the relative strengths of the lines for the most strongly absorbing region, we are able to estimate a gas temperature of $42^{+25}_{-11}$ K and line-of-sight column densities of $N_{CO}=2^{+3}_{-1}\times 10 ^{17} cm^{-2}$ and $N_{ H_{2} }=7^{+10}_{-4}\times 10 ^{20} cm^{-2}$., Comment: 11 pages, 8 figures, accepted to MNRAS

The relative importance of the physical processes shaping the thermodynamics of the hot gas permeating rotating, massive early-type galaxies is expected to be different from that in non-rotating systems. Here, we report the results of the analysis of XMM-Newton data for the massive, lenticular galaxy NGC 7049. The galaxy harbours a dusty disc of cool gas and is surrounded by an extended hot X-ray emitting gaseous atmosphere with unusually high central entropy. The hot gas in the plane of rotation of the cool dusty disc has a multi-temperature structure, consistent with ongoing cooling. We conclude that the rotational support of the hot gas is likely capable of altering the multiphase condensation regardless of the $t_{\rm cool}/t_{\rm ff}$ ratio, which is here relatively high, $\sim 40$. However, the measured ratio of cooling time and eddy turnover time around unity ($C$-ratio $\approx 1$) implies significant condensation, and at the same time, the constrained ratio of rotational velocity and the velocity dispersion (turbulent Taylor number) ${\rm Ta_t} > 1$ indicates that the condensing gas should follow non-radial orbits forming a disc instead of filaments. This is in agreement with hydrodynamical simulations of massive rotating galaxies predicting a similarly extended multiphase disc., Comment: 11 pages, 12 figures, accepted for publication in MNRAS

We present a study of the thermal structure of the hot X-ray emitting atmospheres for a sample of 49 nearby X-ray and optically bright elliptical galaxies using {\it Chandra} X-ray data. We focus on the connection between the properties of the hot X-ray emitting gas and the cooler H$\alpha$+[NII] emitting phase, and the possible role of the latter in the AGN (Active Galactic Nuclei) feedback cycle. We do not find evident correlations between the H$\alpha$+[NII] emission and global properties such as X-ray luminosity, mass of hot gas, and gas mass fraction. We find that the presence of H$\alpha$+[NII] emission is more likely in systems with higher densities, lower entropies, shorter cooling times, shallower entropy profiles, lower values of min($t_{\rm cool}/t_{\rm ff}$), and disturbed X-ray morphologies (linked to turbulent motions). However, we see no clear separations in the observables obtained for galaxies with and without optical emission line nebulae. The AGN jet powers of the galaxies with X-ray cavities show hint of a possible weak positive correlation with their H$\alpha$+[NII] luminosities. This correlation and the observed trends in the thermodynamic properties may result from chaotic cold accretion (CCA) powering AGN jets, as seen in some high-resolution hydrodynamic simulations., Comment: Published in MNRAS

We have selected a sample of eleven massive clusters of galaxies observed by the Hubble Space Telescope in order to study the impact of the dynamical state on the IntraCluster Light (ICL) fraction, the ratio of total integrated ICL to the total galaxy member light. With the exception of the Bullet cluster, the sample is drawn from the Cluster Lensing and Supernova Survey and the Frontier Fields program, containing five relaxed and six merging clusters. The ICL fraction is calculated in three optical filters using the CHEFs IntraCluster Light Estimator, a robust and accurate algorithm free of a priori assumptions. We find that the ICL fraction in the three bands is, on average, higher for the merging clusters, ranging between $\sim7-23\%$, compared with the $\sim 2-11\%$ found for the relaxed systems. We observe a nearly constant value (within the error bars) in the ICL fraction of the regular clusters at the three wavelengths considered, which would indicate that the colors of the ICL and the cluster galaxies are, on average, coincident and, thus, their stellar populations. However, we find a higher ICL fraction in the F606W filter for the merging clusters, consistent with an excess of lower-metallicity/younger stars in the ICL, which could have migrated violently from the outskirts of the infalling galaxies during the merger event., Comment: 25 pages, 13 figures, 2 tables. Accepted for publication in ApJ

The relation between X-ray luminosity (L_X) and ambient gas temperature (T) among massive galactic systems is an important cornerstone of both observational cosmology and galaxy-evolution modeling. In the most massive galaxy clusters, the relation is determined primarily by cosmological structure formation. In less massive systems, it primarily reflects the feedback response to radiative cooling of circumgalactic gas. Here we present a simple but powerful model for the L_X-T relation as a function of physical aperture R within which those measurements are made. The model is based on the precipitation framework for AGN feedback and assumes that the circumgalactic medium is precipitation-regulated at small radii and limited by cosmological structure formation at large radii. We compare this model with many different data sets and show that it successfully reproduces the slope and upper envelope of the L_X-T-R relation over the temperature range from ~0.2 keV through >10 keV. Our findings strongly suggest that the feedback mechanisms responsible for regulating star formation in individual massive galaxies have much in common with the precipitation-triggered feedback that appears to regulate galaxy-cluster cores., Comment: Submitted to ApJ, 9 pages, 3 figures (v2 fixes a few small typos)

We present accurate photometric redshifts for galaxies observed by the Cluster Lensing and Supernova survey with Hubble (CLASH). CLASH observed 25 massive galaxy cluster cores with the Hubble Space Telescope in 16 filters spanning 0.2 - 1.7 $\mu$m. Photometry in such crowded fields is challenging. Compared to our previously released catalogs, we make several improvements to the photometry, including smaller apertures, ICL subtraction, PSF matching, and empirically measured uncertainties. We further improve the Bayesian Photometric Redshift (BPZ) estimates by adding a redder elliptical template and by inflating the photometric uncertainties of the brightest galaxies. The resulting photometric redshift accuracies are dz/(1+z) $\sim$ 0.8\%, 1.0\%, and 2.0\% for galaxies with I-band F814W AB magnitudes $<$ 18, 20, and 23, respectively. These results are consistent with our expectations. They improve on our previously reported accuracies by a factor of 4 at the bright end and a factor of 2 at the faint end. Our new catalog includes 1257 spectroscopic redshifts, including 382 confirmed cluster members. We also provide stellar mass estimates. Finally, we include lensing magnification estimates of background galaxies based on our public lens models. Our new catalog of all 25 CLASH clusters is available via MAST. The analysis techniques developed here will be useful in other surveys of crowded fields, including the Frontier Fields and surveys carried out with J-PAS and JWST., Comment: 21 pages, 21 figures, 5 tables. Photo-z Catalogues Available. Accepted for publication in MNRAS

To investigate the relationship between thermal and non-thermal components in merger galaxy clusters, we present deep JVLA and Chandra observations of the HST Frontier Fields cluster MACS J0717.5+3745. The Chandra image shows a complex merger event, with at least four components belonging to different merging subclusters. NW of the cluster, $\sim 0.7$ Mpc from the center, there is a ram-pressure-stripped core that appears to have traversed the densest parts of the cluster after entering the ICM from the direction of a galaxy filament to the SE. We detect a density discontinuity NNE of this core which we speculate is associated with a cold front. Our radio images reveal new details for the complex radio relic and radio halo in this cluster. In addition, we discover several new filamentary radio sources with sizes of 100-300 kpc. A few of these seem to be connected to the main radio relic, while others are either embedded within the radio halo or projected onto it. A narrow-angled-tailed (NAT) radio galaxy, a cluster member, is located at the center of the radio relic. The steep spectrum tails of this AGN leads into the large radio relic where the radio spectrum flattens again. This morphological connection between the NAT radio galaxy and relic provides evidence for re-acceleration (revival) of fossil electrons. The presence of hot $\gtrsim 20$ keV ICM gas detected by Chandra near the relic location provides additional support for this re-acceleration scenario., Comment: 22 pages, 15 figures, accepted for publication in ApJ

The XXL survey currently covers two 25 sq. deg. patches with XMM observations of ~10ks. We summarise the scientific results associated with the first release of the XXL data set, that occurred mid 2016. We review several arguments for increasing the survey depth to 40 ks during the next decade of XMM operations. X-ray (z<2) cluster, (z<4) AGN and cosmic background survey science will then benefit from an extraordinary data reservoir. This, combined with deep multi-$\lambda$ observations, will lead to solid standalone cosmological constraints and provide a wealth of information on the formation and evolution of AGN, clusters and the X-ray background. In particular, it will offer a unique opportunity to pinpoint the z>1 cluster density. It will eventually constitute a reference study and an ideal calibration field for the upcoming eROSITA and Euclid missions., Comment: Proceeding of the XMM Next Decade Workshop held at ESAC, 9-11 May 2016

We present ALMA CO(1-0) and CO(3-2) observations of the brightest cluster galaxy (BCG) in the 2A 0335+096 galaxy cluster (z = 0.0346). The total molecular gas mass of (1.13+/-0.15) x 10^9 M_sun is divided into two components: a nuclear region and a 7 kpc long dusty filament. The central molecular gas component accounts for (3.2+/-0.4) x 10^8 M_sun of the total supply of cold gas. Instead of forming a rotationally-supported ring or disk, it is composed of two distinct, blueshifted clumps south of the nucleus and a series of low-significance redshifted clumps extending toward a nearby companion galaxy. The velocity of the redshifted clouds increases with radius to a value consistent with the companion galaxy, suggesting that an interaction between these galaxies <20 Myr ago disrupted a pre-existing molecular gas reservoir within the BCG. Most of the molecular gas, (7.8+/-0.9) x 10^8 M_sun, is located in the filament. The CO emission is co-spatial with a 10^4 K emission-line nebula and soft X-rays from 0.5 keV gas, indicating that the molecular gas has cooled out of the intracluster medium over a period of 25-100 Myr. The filament trails an X-ray cavity, suggesting that the gas has cooled from low entropy gas that has been lifted out of the cluster core and become thermally unstable. We are unable to distinguish between inflow and outflow along the filament with the present data. Cloud velocities along the filament are consistent with gravitational free-fall near the plane of the sky, although their increasing blueshifts with radius are consistent with outflow., Comment: 21 pages, 14 figures, accepted to ApJ

We provide an analytic framework for interpreting observations of multiphase circumgalactic gas that is heavily informed by recent numerical simulations of thermal instability and precipitation in cool-core galaxy clusters. We start by considering the local conditions required for the formation of multiphase gas via two different modes: (1) uplift of ambient gas by galactic outflows, and (2) condensation in a stratified stationary medium in which thermal balance is explicitly maintained. Analytic exploration of these two modes provides insights into the relationships between the local ratio of the cooling and freefall time scales (i.e., t_cool / t_ff), the large-scale gradient of specific entropy, and development of precipitation and multiphase media in circumgalactic gas. We then use these analytic findings to interpret recent simulations of circumgalactic gas in which global thermal balance is maintained. We show that long-lasting configurations of gas with 5 < t_cool / t_ff < 20 and radial entropy profiles similar to observations of local cool-core galaxy cluster cores are a natural outcome of precipitation-regulated feedback. We conclude with some observational predictions that follow from these models. This work focuses primarily on precipitation and AGN feedback in galaxy cluster cores, because that is where the observations of multiphase gas around galaxies are most complete. However, many of the physical principles that govern condensation in those environments apply to circumgalactic gas around galaxies of all masses., Comment: ApJ, in press (30 pages, 10 figures). The accepted version improves upon the previous one by showing how saturation of thermally unstable gravity waves can arise from non-linear coupling to pairs of sound-waves with a resonant beat frequency. This mode of saturation is now called "buoyancy damping" but in previous versions was called "convective damping."

The HST Frontier Fields cluster MACS J1149.6+2223 is one of the most complex merging clusters, believed to consist of four dark matter halos. We present results from deep (365 ks) Chandra observations of the cluster, which reveal the most distant cold front (z=0.544) discovered to date. In the cluster outskirts, we also detect hints of a surface brightness edge that could be the bow shock preceding the cold front. The substructure analysis of the cluster identified several components with large relative radial velocities, thus indicating that at least some collisions occur almost along the line of sight. The inclination of the mergers with respect to the plane of the sky poses significant observational challenges at X-ray wavelengths. MACS J1149.6+2223 possibly hosts a steep-spectrum radio halo. If the steepness of the radio halo is confirmed, then the radio spectrum, combined with the relatively regular ICM morphology, could indicate that MACS J1149.6+2223 is an old merging cluster., Comment: Accepted to ApJ

We present ALMA observations of the CO(1-0) and CO(3-2) line emission tracing filaments of cold molecular gas in the central galaxy of the cluster PKS0745-191. The total molecular gas mass of 4.6 +/- 0.3 x 10^9 solar masses, assuming a Galactic X_{CO} factor, is divided roughly equally between three filaments each extending radially 3-5 kpc from the galaxy centre. The emission peak is located in the SE filament roughly 1 arcsec (2 kpc) from the nucleus. The velocities of the molecular clouds in the filaments are low, lying within +/-100 km/s of the galaxy's systemic velocity. Their FWHMs are less than 150 km/s, which is significantly below the stellar velocity dispersion. Although the molecular mass of each filament is comparable to a rich spiral galaxy, such low velocities show that the filaments are transient and the clouds would disperse on <10^7 yr timescales unless supported, likely by the indirect effect of magnetic fields. The velocity structure is inconsistent with a merger origin or gravitational free-fall of cooling gas in this massive central galaxy. If the molecular clouds originated in gas cooling even a few kpc from their current locations their velocities would exceed those observed. Instead, the projection of the N and SE filaments underneath X-ray cavities suggests they formed in the updraft behind bubbles buoyantly rising through the cluster atmosphere. Direct uplift of the dense gas by the radio bubbles appears to require an implausibly high coupling efficiency. The filaments are coincident with low temperature X-ray gas, bright optical line emission and dust lanes indicating that the molecular gas could have formed from lifted warmer gas that cooled in situ., Comment: 16 pages, 10 figures, accepted by MNRAS

We report on high-resolution JVLA and Chandra observations of the HST Frontier Cluster MACS J0717.5+3745. MACS J0717.5+3745 offers the largest contiguous magnified area of any known cluster, making it a promising target to search for lensed radio and X-ray sources. With the high-resolution 1.0-6.5 GHz JVLA imaging in A and B configuration, we detect a total of 51 compact radio sources within the area covered by the HST imaging. Within this sample we find 7 lensed sources with amplification factors larger than $2$. None of these sources are identified as multiply-lensed. Based on the radio luminosities, the majority of these sources are likely star forming galaxies with star formation rates of 10-50 M$_\odot$ yr$^{-1}$ located at $1 \lesssim z \lesssim 2$. Two of the lensed radio sources are also detected in the Chandra image of the cluster. These two sources are likely AGN, given their $2-10$ keV X-ray luminosities of $\sim 10^{43-44}$ erg s$^{-1}$. From the derived radio luminosity function, we find evidence for an increase in the number density of radio sources at $0.6

A fraction of brightest cluster galaxies (BCGs) shows bright emission in the UV and the blue part of the optical spectrum, which has been interpreted as evidence of recent star formation. Most of these results are based on the analysis of broadband photometric data. Here, we study the optical spectra of a sample of 19 BCGs hosted by X-ray luminous galaxy clusters at 0.15 < z < 0.3, a subset from the Canadian Cluster Comparison Project (CCCP) sample. We identify plausible star formation histories of the galaxies by fitting Simple Stellar Populations (SSPs) as well as composite populations, consisting of a young stellar component superimposed on an intermediate/old stellar component, to accurately constrain their star formation histories. We detect prominent young (~200 Myr) stellar populations in 4 of the 19 galaxies. Of the four, the BCG in Abell 1835 shows remarkable A-type stellar features indicating a relatively large population of young stars, which is extremely unusual even amongst star forming BCGs. We constrain the mass contribution of these young components to the total stellar mass to be typically between 1% to 3%, but rising to 7% in Abell 1835. We find that the four of the BCGs with strong evidence for recent star formation (and only these four galaxies) are found within a projected distance of 5 kpc of their host cluster's X-ray peak, and the diffuse, X-ray gas surrounding the BCGs exhibit a ratio of the radiative cooling-to-free-fall time ($t_{c}/t_{ff}$) of < 10. These are also some of the clusters with the lowest central entropy. Our results are consistent with the predictions of the precipitation-driven star formation and AGN feedback model, in which the radiatively cooling diffuse gas is subject to local thermal instabilities once the instability parameter $t_{c}/t_{ff}$ falls below ~10, leading to the condensation and precipitation of cold gas. [Abridged], Comment: 16 pages, accepted for publication in MNRAS

We present VIMOS-VLT spectroscopy of the Frontier Fields cluster MACS~J0416.1-2403 (z=0.397). Taken as part of the CLASH-VLT survey, the large spectroscopic campaign provided more than 4000 reliable redshifts, including ~800 cluster member galaxies. The unprecedented sample of cluster members at this redshift allows us to perform a highly detailed dynamical and structural analysis of the cluster out to ~2.2$r_{200}$ (~4Mpc). Our analysis of substructures reveals a complex system composed of a main massive cluster ($M_{200}$~0.9$\times 10^{15} M_{\odot}$) presenting two major features: i) a bimodal velocity distribution, showing two central peaks separated by $\Delta V_{rf}$~1100 km s$^{-1}$ with comparable galaxy content and velocity dispersion, ii) a projected elongation of the main substructures along the NE-SW direction, with a prominent subclump ~600 kpc SW of the center and an isolated BCG approximately halfway between the center and the SW clump. We also detect a low mass structure at z~0.390, ~10' S of the cluster center, projected at ~3Mpc, with a relative line-of-sight velocity of $\Delta V_{rf}$~-1700 km s$^{-1}$. The cluster mass profile that we obtain through our dynamical analysis deviates significantly from the "universal" NFW, being best fit by a Softened Isothermal Sphere model instead. The mass profile measured from the galaxy dynamics is found to be in relatively good agreement with those obtained from strong and weak lensing, as well as with that from the X-rays, despite the clearly unrelaxed nature of the cluster. Our results reveal overall a complex dynamical state of this massive cluster and support the hypothesis that the two main subclusters are being observed in a pre-collisional phase, in line with recent findings from radio and deep X-ray data. With this article we also release the entire redshift catalog of 4386 sources in the field of this cluster., Comment: Accepted for publication on ApJS. Revised to match the accepted version; 21 pages, 18 figures, 9 tables. The CLASH-VLT spectroscopic catalogs are publicly available at: http://sites.google.com/site/vltclashpublic/

We present a dynamical analysis of the merging galaxy cluster system Abell 2146 using spectroscopy obtained with the Gemini Multi-Object Spectrograph on the Gemini North telescope. As revealed by the Chandra X-ray Observatory, the system is undergoing a major merger and has a gas structure indicative of a recent first core passage. The system presents two large shock fronts, making it unique amongst these rare systems. The hot gas structure indicates that the merger axis must be close to the plane of the sky and that the two merging clusters are relatively close in mass, from the observation of two shock fronts. Using 63 spectroscopically determined cluster members, we apply various statistical tests to establish the presence of two distinct massive structures. With the caveat that the system has recently undergone a major merger, the virial mass estimate is M_vir = 8.5 +4.3 -4.7 x 10 ^14 M_sol for the whole system, consistent with the mass determination in a previous study using the Sunyaev-Zeldovich signal. The newly calculated redshift for the system is z = 0.2323. A two-body dynamical model gives an angle of 13-19 degrees between the merger axis and the plane of the sky, and a timescale after first core passage of 0.24-0.28 Gyr., Comment: Accepted in MNRAS on August 6 2015. 15 pages, 8 figures, 1 Table

Merging galaxy clusters leave long-lasting signatures on the baryonic and non-baryonic cluster constituents, including shock fronts, cold fronts, X-ray substructure, radio halos, and offsets between the dark matter and the gas components. Using observations from Chandra, the Jansky Very Large Array, the Giant Metrewave Radio Telescope, and the Hubble Space Telescope, we present a multiwavelength analysis of the merging Frontier Fields cluster MACS J0416.1-2403 (z=0.396), which consists of a NE and a SW subclusters whose cores are separated on the sky by ~250 kpc. We find that the NE subcluster has a compact core and hosts an X-ray cavity, yet it is not a cool core. Approximately 450 kpc south-south west of the SW subcluster, we detect a density discontinuity that corresponds to a compression factor of ~1.5. The discontinuity was most likely caused by the interaction of the SW subcluster with a less massive structure detected in the lensing maps SW of the subcluster's center. For both the NE and the SW subclusters, the dark matter and the gas components are well-aligned, suggesting that MACS J0416.1-2403 is a pre-merging system. The cluster also hosts a radio halo, which is unusual for a pre-merging system. The halo has a 1.4 GHz power of (1.06 +/- 0.09) x 10^{24} W Hz^{-1}, which is somewhat lower than expected based on the X-ray luminosity of the cluster. We suggest that we are either witnessing the birth of a radio halo, or have discovered a rare ultra-steep spectrum halo., Comment: Submitted to ApJ. Comments are welcome

We present results from a very deep (650 ks) Chandra X-ray observation of the galaxy group NGC~5813, the deepest Chandra observation of a galaxy group to date. Earlier observations showed two pairs of cavities distributed roughly collinearly, with each pair associated with an elliptical shock front. The new observations confirm a third pair of outer cavities, collinear with the other pairs, and reveal an associated outer outburst shock at ~30 kpc. This system is therefore unique in exhibiting three cavity pairs, each associated with an unambiguous AGN outburst shock front. The implied mean kinetic power is roughly the same for each outburst, demonstrating that the average AGN kinetic luminosity can remain stable over long timescales (~50 Myr). The two older outbursts have larger, roughly equal total energies as compared with the youngest outburst, implying that the youngest outburst is ongoing. We find that the radiative cooling rate and the mean shock heating rate of the gas are well balanced at each shock front, suggesting that AGN outburst shock heating alone is sufficient to offset cooling and establish AGN/ICM feedback within at least the central 30 kpc. This heating takes place roughly isotropically and most strongly at small radii, as is required for feedback to operate. We suggest that shock heating may play a significant role in AGN feedback at smaller radii in other systems, where weak shocks are more difficult to detect. We find non-zero shock front widths that are too large to be explained by particle diffusion. Instead, all measured widths are consistent with shock broadening due to propagation through a turbulent ICM with a mean turbulent speed of ~70 km/s. Finally, we place lower limits on the temperature of any volume-filling thermal gas within the cavities that would balance the internal cavity pressure with the external ICM., Comment: 24 pages, 15 figures, accepted for publication in ApJ

This report describes the 2014 study by the Science Definition Team (SDT) of the Wide-Field Infrared Survey Telescope (WFIRST) mission. It is a space observatory that will address the most compelling scientific problems in dark energy, exoplanets and general astrophysics using a 2.4-m telescope with a wide-field infrared instrument and an optical coronagraph. The Astro2010 Decadal Survey recommended a Wide Field Infrared Survey Telescope as its top priority for a new large space mission. As conceived by the decadal survey, WFIRST would carry out a dark energy science program, a microlensing program to determine the demographics of exoplanets, and a general observing program utilizing its ultra wide field. In October 2012, NASA chartered a Science Definition Team (SDT) to produce, in collaboration with the WFIRST Study Office at GSFC and the Program Office at JPL, a Design Reference Mission (DRM) for an implementation of WFIRST using one of the 2.4-m, Hubble-quality telescope assemblies recently made available to NASA. This DRM builds on the work of the earlier WFIRST SDT, reported by Green et al. (2012) and the previous WFIRST-2.4 DRM, reported by Spergel et. (2013). The 2.4-m primary mirror enables a mission with greater sensitivity and higher angular resolution than the 1.3-m and 1.1-m designs considered previously, increasing both the science return of the primary surveys and the capabilities of WFIRST as a Guest Observer facility. The addition of an on-axis coronagraphic instrument to the baseline design enables imaging and spectroscopic studies of planets around nearby stars., Comment: This report describes the 2014 study by the Science Definition Team of the Wide-Field Infrared Survey Telescope mission. 319 pages; corrected a misspelled name in the authors list and a typo in the abstract

Most of the massive elliptical galaxies in the universe stopped forming stars billions of years ago, even though plenty of hot gas remains available for star formation. Here we present compelling evidence indicating that quenching of star formation depends on both black-hole feedback and Type Ia supernova heating. We analyze Chandra X-ray observations of ten massive ellipticals, five with extended, potentially star-forming multiphase gas and five single-phase ellipticals with no star formation. The ratio of cooling time to freefall time at 1--10 kpc in the multiphase galaxies is tc/tff ~10, indicating that precipitation-driven feedback limits cooling but does not eliminate condensation. In the same region of the single-phase galaxies, the radial profiles of gas entropy are consistent with a thermally stable (tc/tff > 20) supernova-driven outflow that sweeps stellar ejecta out of the galaxy. However, in one of those single-phase ellipticals (NGC 4261) we find tc/tff < 10 at < 300 pc. Notably, its jets are ~50 times more powerful than in the other nine ellipticals, in agreement with models indicating that precipitation near the black hole should switch its fueling mode from Bondi-like accretion to cold chaotic accretion. We conclude by hypothesizing that particularly strong black-hole outbursts can shut off star formation in massive elliptical galaxies by boosting the entropy of the hot gas and flipping the system into the supernova-sweeping state., Comment: ApJ Letters, in press, 5 pages, 2 figures, some typos corrected in v2

Star formation in the universe's largest galaxies---the ones at the centers of galaxy clusters---depends critically on the thermodynamic state of their hot gaseous atmospheres. Central galaxies with low-entropy, high-density atmospheres frequently contain multiphase star-forming gas, while those with high-entropy, low-density atmospheres never do. The dividing line between these two populations in central entropy, and therefore central cooling time, is amazingly sharp. Two hypotheses have been proposed to explain the dichotomy. One points out that thermal conduction can prevent radiative cooling of cluster cores above the dividing line. The other holds that cores below the dividing line are subject to thermal instability that fuels the central AGN through a cold-feedback mechanism. Here we explore those hypotheses with an analysis of the H-alpha properties of ACCEPT galaxy clusters. We find that the two hypotheses are likely to be complementary. Our results support a picture in which cold clouds inevitably precipitate out of cluster cores in which cooling outcompetes thermal conduction and rain down on the central black hole, causing AGN feedback that stabilizes the cluster core. In particular, the observed distribution of the cooling-time to freefall-time ratio is nearly identical to that seen in simulations of this cold-feedback process, implying that cold-phase accretion, and not Bondi-like accretion of hot-phase gas, is responsible for the AGN feedback that regulates star formation in large galaxies., Comment: Submitted to ApJ Letters

The universe's largest galaxies reside at the centers of galaxy clusters and are embedded in hot gas that, if left unchecked, would cool prodigiously and create many more new stars than are actually observed. Cooling can be regulated by feedback from accretion of cooling gas onto the central black hole, but requires an accretion rate finely tuned to the thermodynamic state of the hot gas. Theoretical models in which cold clouds precipitate out of the hot gas via thermal instability and accrete onto the black hole exhibit the necessary tuning. We have recently presented observational evidence showing that the abundance of cold gas in the central galaxy increases rapidly near the predicted threshold for instability. Here we present observations showing that this threshold extends over a large range in cluster radius, cluster mass, and cosmic time, and incorporate the precipitation threshold into a comprehensive framework of theoretical models for the thermodynamic state of hot gas in galaxy clusters. According to that framework, precipitation regulates star formation in some giant galaxies, while thermal conduction prevents star formation in others, if it can compensate for radiative cooling and shut off precipitation., Comment: Nature (submitted 3 Sep 2014, accepted 22 Dec 14, published online 4 Mar 15): http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14167.html

Context. The study of the galaxy stellar mass function (SMF) in relation to the galaxy environment and the stellar mass density profile, rho(r), is a powerful tool to constrain models of galaxy evolution. Aims. We determine the SMF of the z=0.44 cluster of galaxies MACS J1206.2-0847 separately for passive and star-forming (SF) galaxies, in different regions of the cluster, from the center out to approximately 2 virial radii. We also determine rho(r) to compare it to the number density and total mass density profiles. Methods. We use the dataset from the CLASH-VLT survey. Stellar masses are obtained by SED fitting on 5-band photometric data obtained at the Subaru telescope. We identify 1363 cluster members down to a stellar mass of 10^9.5 Msolar. Results. The whole cluster SMF is well fitted by a double Schechter function. The SMFs of cluster SF and passive galaxies are statistically different. The SMF of the SF cluster galaxies does not depend on the environment. The SMF of the passive population has a significantly smaller slope (in absolute value) in the innermost (<0.50 Mpc), highest density cluster region, than in more external, lower density regions. The number ratio of giant/subgiant galaxies is maximum in this innermost region and minimum in the adjacent region, but then gently increases again toward the cluster outskirts. This is also reflected in a decreasing radial trend of the average stellar mass per cluster galaxy. On the other hand, the stellar mass fraction, i.e., the ratio of stellar to total cluster mass, does not show any significant radial trend. Conclusions. Our results appear consistent with a scenario in which SF galaxies evolve into passive galaxies due to density-dependent environmental processes, and eventually get destroyed very near the cluster center to become part of a diffuse intracluster medium., Comment: A&A accepted, 15 pages, 13 figures

We present a new Chandra X-ray observation of the off-axis galaxy group merger RXJ0751.3+5012. The hot atmospheres of the two colliding groups appear highly distorted by the merger. The images reveal arc-like cold fronts around each group core, produced by the motion through the ambient medium, and the first detection of a group merger shock front. We detect a clear density and temperature jump associated with a bow shock of Mach number M=1.9+/-0.4 ahead of the northern group. Using galaxy redshifts and the shock velocity of 1100+/-300 km/s, we estimate that the merger axis is only 10deg from the plane of the sky. From the projected group separation of 90 kpc, this corresponds to a time since closest approach of 0.1 Gyr. The northern group hosts a dense, cool core with a ram pressure stripped tail of gas extending 100 kpc. The sheared sides of this tail appear distorted and broadened by Kelvin-Helmholtz instabilities. We use the presence of this substructure to place an upper limit on the magnetic field strength and, for Spitzer-like viscosity, show that the development of these structures is consistent with the critical perturbation length above which instabilities can grow in the intragroup medium. The northern group core also hosts a galaxy pair, UGC4052, with a surrounding IR and near-UV ring 40 kpc in diameter. The ring may have been produced by tidal stripping of a smaller galaxy by UGC4052 or it may be a collisional ring generated by a close encounter between the two large galaxies., Comment: 14 pages, 12 figures, accepted by MNRAS

We present the results of a numerical study based on the analysis of the MUSIC-2 simulations, aimed at estimating the expected concentration-mass relation for the CLASH cluster sample. We study nearly 1400 halos simulated at high spatial and mass resolution, which were projected along many lines-of-sight each. We study the shape of both their density and surface-density profiles and fit them with a variety of radial functions, including the Navarro-Frenk-White, the generalised Navarro-Frenk-White, and the Einasto density profiles. We derive concentrations and masses from these fits and investigate their distributions as a function of redshift and halo relaxation. We use the X-ray image simulator X-MAS to produce simulated Chandra observations of the halos and we use them to identify objects resembling the X-ray morphologies and masses of the clusters in the CLASH X-ray selected sample. We also derive a concentration-mass relation for strong-lensing clusters. We find that the sample of simulated halos which resemble the X-ray morphology of the CLASH clusters is composed mainly by relaxed halos, but it also contains a significant fraction of un-relaxed systems. For such a sample we measure an average 2D concentration which is ~11% higher than found for the full sample of simulated halos. After accounting for projection and selection effects, the average NFW concentrations of CLASH clusters are expected to be intermediate between those predicted in 3D for relaxed and super-relaxed halos. Matching the simulations to the individual CLASH clusters on the basis of the X-ray morphology, we expect that the NFW concentrations recovered from the lensing analysis of the CLASH clusters are in the range [3-6], with an average value of 3.87 and a standard deviation of 0.61. Simulated halos with X-ray morphologies similar to those of the CLASH clusters are affected by a modest orientation bias., Comment: 21 pages, 16 figures, 3 tables, submitted to ApJ

We present a new determination of the concentration-mass relation for galaxy clusters based on our comprehensive lensing analysis of 19 X-ray selected galaxy clusters from the Cluster Lensing and Supernova Survey with Hubble (CLASH). Our sample spans a redshift range between 0.19 and 0.89. We combine weak lensing constraints from the Hubble Space Telescope (HST) and from ground-based wide field data with strong lensing constraints from HST. The result are reconstructions of the surface-mass density for all CLASH clusters on multi-scale grids. Our derivation of NFW parameters yields virial masses between 0.53 x 10^15 and 1.76 x 10^15 M_sol/h and the halo concentrations are distributed around c_200c ~ 3.7 with a 1-sigma significant negative trend with cluster mass. We find an excellent 4% agreement between our measured concentrations and the expectation from numerical simulations after accounting for the CLASH selection function based on X-ray morphology. The simulations are analyzed in 2D to account for possible biases in the lensing reconstructions due to projection effects. The theoretical concentration-mass (c-M) relation from our X-ray selected set of simulated clusters and the c-M relation derived directly from the CLASH data agree at the 90% confidence level., Comment: 24 pages, 15 figures and 10 tables. Submitted to ApJ. (Minor, non-scientific changes since ver1, added acknowledgement, added arXiv references to companion papers, fixed arXiv author list mistake.)

We aim at constraining the assembly history of clusters by studying the intra cluster light (ICL) properties, estimating its contribution to the fraction of baryons in stars, f*, and understanding possible systematics/bias using different ICL detection techniques. We developed an automated method, GALtoICL, based on the software GALAPAGOS to obtain a refined version of typical BCG+ICL maps. We applied this method to our test case MACS J1206.2-0847, a massive cluster located at z=0.44, that is part of the CLASH sample. Using deep multi-band SUBARU images, we extracted the surface brightness (SB) profile of the BCG+ICL and we studied the ICL morphology, color, and contribution to f* out to R500. We repeated the same analysis using a different definition of the ICL, SBlimit method, i.e. a SB cut-off level, to compare the results. The most peculiar feature of the ICL in MACS1206 is its asymmetric radial distribution, with an excess in the SE direction and extending towards the 2nd brightest cluster galaxy which is a Post Starburst galaxy. This suggests an interaction between the BCG and this galaxy that dates back to t <= 1.5 Gyr. The BCG+ICL stellar content is 8% of M_(*,500) and the (de-) projected baryon fraction in stars is f*=0.0177 (0.0116), in excellent agreement with recent results. The SBlimit method provides systematically higher ICL fractions and this effect is larger at lower SB limits. This is due to the light from the outer envelopes of member galaxies that contaminate the ICL. Though more time consuming, the GALtoICL method provides safer ICL detections that are almost free of this contamination. This is one of the few ICL study at redshift z > 0.3. At completion, the CLASH/VLT program will allow us to extend this analysis to a statistically significant cluster sample spanning a wide redshift range: 0.2

We report ALMA Early Science observations of the Abell 1835 brightest cluster galaxy (BCG) in the CO (3-2) and CO (1-0) emission lines. We detect $5\times 10^{10}~\rm M_\odot$ of molecular gas within 10 kpc of the BCG. Its ensemble velocity profile width of $\sim 130 ~\rm km~s^{-1}$ FWHM is too narrow for the molecular cloud sto be supported in the galaxy by dynamic pressure. The gas may instead be supported in a rotating, turbulent disk oriented nearly face-on. Roughly $10^{10}~\rm M_\odot$ of molecular gas is projected $3-10 ~\rm kpc$ to the north-west and to the east of the nucleus with line of sight velocities lying between $-250 ~\rm km~s^{-1}$ to $+480 ~\rm km~s^{-1}$ with respect to the systemic velocity. The high velocity gas may be either inflowing or outflowing. However, the absence of high velocity gas toward the nucleus that would be expected in a steady inflow, and its bipolar distribution on either side of the nucleus, are more naturally explained as outflow. Star formation and radiation from the AGN are both incapable of driving an outflow of this magnitude. If so, the molecular outflow may be associated a hot outflow on larger scales reported by Kirkpatrick and colleagues. The molecular gas flow rate of approximately $200~\rm M_\odot ~yr^{-1}$ is comparable to the star formation rate of $100-180~\rm M_\odot ~yr^{-1}$ in the central disk. How radio bubbles would lift dense molecular gas in their updrafts, how much gas will be lost to the BCG, and how much will return to fuel future star formation and AGN activity are poorly understood. Our results imply that radio-mechanical (radio mode) feedback not only heats hot atmospheres surrounding elliptical galaxies and BCGs, it is able to sweep higher density molecular gas away from their centers., Comment: To appear in ApJ -- expanded discussion of inflow/outflow added to submitted version

We present a strong lensing system in which a double source is imaged 5 times by 2 early-type galaxies. We take advantage in this target of the multi-band photometry obtained as part of the CLASH program, complemented by the spectroscopic data of the VLT/VIMOS and FORS2 follow-up campaign. We use a photometric redshift of 3.7 for the source and confirm spectroscopically the membership of the 2 lenses to the galaxy cluster MACS J1206.2-0847 at redshift 0.44. We exploit the excellent angular resolution of the HST/ACS images to model the 2 lenses in terms of singular isothermal sphere profiles and derive robust effective velocity dispersions of (97 +/- 3) and (240 +/- 6) km/s. The total mass distribution of the cluster is also well characterized by using only the local information contained in this lensing system, that is located at a projected distance of more than 300 kpc from the cluster luminosity center. According to our best-fitting lensing and composite stellar population models, the source is magnified by a total factor of 50 and has a luminous mass of about (1.0 +/- 0.5) x 10^{9} M_{Sun}. By combining the total and luminous mass estimates of the 2 lenses, we measure luminous over total mass fractions projected within the effective radii of 0.51 +/- 0.21 and 0.80 +/- 0.32. With these lenses we can extend the analysis of the mass properties of lens early-type galaxies by factors that are about 2 and 3 times smaller than previously done with regard to, respectively, velocity dispersion and luminous mass. The comparison of the total and luminous quantities of our lenses with those of astrophysical objects with different physical scales reveals the potential of studies of this kind for investigating the internal structure of galaxies. These studies, made possible thanks to the CLASH survey, will allow us to go beyond the current limits posed by the available lens samples in the field., Comment: 20 pages, 10 figures, accepted for publication in the Astrophysical Journal

We present a multi-wavelength study of the interstellar medium in eight nearby, X-ray and optically bright, giant elliptical galaxies. Using Herschel PACS, we map the cold gas in the lines of [CII], [OI], and [OIb]. Additionally, we present Ha+[NII] imaging of warm ionized gas with the SOAR telescope, and a study of the hot X-ray emitting plasma with Chandra. All systems with extended Ha emission in our sample (6/8 galaxies) display significant [CII] line emission indicating the presence of cold gas. This emission is co-spatial with the Ha+[NII] emitting nebulae and the lowest entropy X-ray emitting plasma. The entropy profiles of the hot galactic atmospheres show a clear dichotomy, with the systems displaying extended emission line nebulae having lower entropies beyond r~1 kpc than the cold-gas-poor systems. We show that while the hot atmospheres of the cold-gas-poor galaxies are thermally stable outside of their innermost cores, the atmospheres of the cold-gas-rich systems are prone to cooling instabilities. This result indicates that the cold gas is produced chiefly by thermally unstable cooling from the hot phase. We show that cooling instabilities may develop more easily in rotating systems and discuss an alternative condition for thermal instability for this case. The hot atmospheres of cold-gas-rich galaxies display disturbed morphologies indicating that the accretion of clumpy multiphase gas in these systems may result in variable power output of the AGN jets, potentially triggering sporadic, larger outbursts. In the two cold-gas-poor, X-ray morphologically relaxed galaxies of our sample, NGC 1399 and NGC 4472, powerful AGN outbursts may have destroyed or removed most of the cold gas from the cores, allowing the jets to propagate and deposit most of their energy further out, increasing the entropy of the hot galactic atmospheres and leaving their cores relatively undisturbed., Comment: MNRAS in press