Search

We present a new approach to observationally constrain where the tails of Jellyfish (JF) galaxies in groups and clusters first appear and how long they remain visible with respect to the moment of their orbital pericenter. This is accomplished by measuring the distribution of their tail directions with respect to their host's center, and their distribution in a projected velocity-radius phase-diagram. We then model these observed distributions using a fast and flexible approach where JF tails are painted onto dark matter halos according to a simple parameterised prescription, and perform a Bayesian analysis to estimate the parameters. We demonstrate the effectiveness of our approach using observational mocks, and then apply it to a known observational sample of 106 JF galaxies with radio continuum tails located inside 68 hosts such as groups and clusters. We find that, typically, the radio continuum tails become visible on first infall when the galaxy reaches roughly three quarters of r$_{200}$, and the tails remain visible for a few hundred Myr after pericenter passage. Lower mass galaxies in more massive hosts tend to form visible tails further out and their tails disappear more quickly after pericenter. We argue that this indicates they are more sensitive to ram pressure stripping. With upcoming large area surveys of JF galaxies in progress, this is a promising new method to constrain the environmental conditions in which visible JF tails exist., Accepted to ApJ June 2022, 24 pages, 13 figures, 2 tables

We present the first study of the effect of ram-pressure "unwinding" the spiral arms of cluster galaxies. We study 11 ram-pressure stripped galaxies from GASP (GAs Stripping Phenomena in galaxies) in which, in addition to more commonly observed "jellyfish" features, dislodged material also appears to retain the original structure of the spiral arms. Gravitational influence from neighbours is ruled out and we compare the sample with a control group of undisturbed spiral galaxies and simulated stripped galaxies. We first confirm the unwinding nature, finding the spiral arm pitch angle increases radially in 10 stripped galaxies and also simulated face-on and edge-on stripped galaxies. We find only younger stars in the unwound component, while older stars in the disc remain undisturbed. We compare the morphology and kinematics with simulated ram-pressure stripping galaxies, taking into account the estimated inclination with respect to the intracluster medium and find that in edge-on stripping, unwinding can occur due to differential ram-pressure caused by the disc rotation, causing stripped material to slow and "pile-up". In face-on cases, gas removed from the outer edges falls to higher orbits, appearing to "unwind". The pattern is fairly short-lived (, Accepted for publication in MNRAS, 30 pages, 17 figures

We present JVLA-C observations of the HI gas in JO204, one of the most striking jellyfish galaxies from the GASP survey. JO204 is a massive galaxy in the low-mass cluster Abell 957 at z=0.04243. The HI map reveals an extended 90 kpc long ram-pressure stripped tail of neutral gas, stretching beyond the 30 kpc long ionized gas tail and pointing away from the cluster center. The HI mass seen in emission is (1.32 $ \pm 0.13) \times 10^{9} \rm M_{\odot}$, mostly located in the tail. The northern part of the galaxy disk has retained some HI gas, while the southern part has already been completely stripped and displaced into an extended unilateral tail. Comparing the distribution and kinematics of the neutral and ionized gas in the tail indicates a highly turbulent medium. Moreover, we observe associated HI absorption against the 11 mJy central radio continuum source with an estimated HI absorption column density of 3.2 $\times 10^{20}$ cm$^{-2}$. The absorption profile is significantly asymmetric with a wing towards higher velocities. We modelled the HI absorption by assuming that the HI and ionized gas disks have the same kinematics in front of the central continuum source, and deduced a wider absorption profile than observed. The observed asymmetric absorption profile can therefore be explained by a clumpy, rotating HI gas disk seen partially in front of the central continuum source, or by ram-pressure pushing the neutral gas towards the center of the continuum source, triggering the AGN activity., Comment: 16 pages, 10 figures, accepted for publication in MNRAS

Cluster spiral galaxies suffer catastrophic losses of the cool, neutral gas component of their interstellar medium due to ram pressure stripping, contributing to the observed quenching of star formation in the disk compared to galaxies in lower density environments. However, the short term effects of ram pressure on the star formation rate and AGN activity of galaxies undergoing stripping remain unclear. Numerical studies have recently demonstrated cosmic rays can dramatically influence galaxy evolution for isolated galaxies, yet their influence on ram pressure stripping remains poorly constrained. We perform the first cosmic-ray magneto-hydrodynamic simulations of an $L_{*}$ galaxy undergoing ram pressure stripping, including radiative cooling, self-gravity of the gas, star formation, and stellar feedback. We find the microscopic transport of cosmic rays plays a key role in modulating the star formation enhancement experienced by spirals at the outskirts of clusters compared to isolated spirals. Moreover, we find that galaxies undergoing ram pressure stripping exhibit enhanced gas accretion onto their centers, which may explain the prevalence of AGN in these objects. In agreement with observations, we find cosmic rays significantly boost the global radio emission of cluster spirals. Although the gas removal rate is relatively insensitive to cosmic ray physics, we find that cosmic rays significantly modify the phase distribution of the remaining gas disk. These results suggest observations of galaxies undergoing ram pressure stripping may place novel constraints on cosmic-ray calorimetry and transport., 15 pages, 10 figures, submitted to MNRAS

Galaxies can be characterized by many internal properties such as stellar mass, gas metallicity, and star-formation rate. We quantify the amount of cosmological and astrophysical information that the internal properties of individual galaxies and their host dark matter halos contain. We train neural networks using hundreds of thousands of galaxies from 2,000 state-of-the-art hydrodynamic simulations with different cosmologies and astrophysical models of the CAMELS project to perform likelihood-free inference on the value of the cosmological and astrophysical parameters. We find that knowing the internal properties of a single galaxy allow our models to infer the value of $\Omega_{\rm m}$, at fixed $\Omega_{\rm b}$, with a $\sim10\%$ precision, while no constraint can be placed on $\sigma_8$. Our results hold for any type of galaxy, central or satellite, massive or dwarf, at all considered redshifts, $z\leq3$, and they incorporate uncertainties in astrophysics as modeled in CAMELS. However, our models are not robust to changes in subgrid physics due to the large intrinsic differences the two considered models imprint on galaxy properties. We find that the stellar mass, stellar metallicity, and maximum circular velocity are among the most important galaxy properties to determine the value of $\Omega_{\rm m}$. We believe that our results can be explained taking into account that changes in the value of $\Omega_{\rm m}$, or potentially $\Omega_{\rm b}/\Omega_{\rm m}$, affect the dark matter content of galaxies. That effect leaves a distinct signature in galaxy properties to the one induced by galactic processes. Our results suggest that the low-dimensional manifold hosting galaxy properties provides a tight direct link between cosmology and astrophysics., Comment: 20+6 pages, 15 figures, data and codes to reproduce the results publicly available at https://github.com/franciscovillaescusa/Cosmo1gal

The driving of turbulence in galaxies is deeply connected with the physics of feedback, star formation, outflows, accretion, and radial transport in disks. The velocity dispersion of gas in galaxies therefore offers a promising observational window into these processes. However, the relative importance of each of these mechanisms remains controversial. In this work we revisit the possibility that turbulence on galactic scales is driven by the direct impact of accreting gaseous material on the disk. We measure this effect in a disk-like star-forming galaxy in IllustrisTNG, using the high-resolution cosmological magnetohydrodynamical simulation TNG50. We employ Lagrangian tracer particles with a high time cadence of only a few Myr to identify accretion and other events, such as star formation, outflows, and movement within the disk. The energies of particles as they arrive in the disk are measured by stacking the events in bins of time before and after the event. The average effect of each event is measured on the galaxy by fitting explicit models for the kinetic and turbulent energies as a function of time in the disk. These measurements are corroborated by measuring the cross-correlation of the turbulent energy in the different annuli of the disk with other time series, and searching for signals of causality, i.e. asymmetries in the cross-correlation across zero time lag. We find that accretion contributes to the large-scale turbulent kinetic energy even if it is not the dominant driver of turbulence in this $\sim 5 \times 10^{9} M_\odot$ stellar mass galaxy. Extrapolating this finding to a range of galaxy masses, we find that there are regimes where energy from direct accretion may dominate the turbulent energy budget, particularly in disk outskirts, galaxies less massive than the Milky Way, and at redshift $\sim 2$., Comment: Submitted to AAS Journals, comments welcome

We present the Virgo Environment Traced in CO (VERTICO) survey, a new effort to map $^{12}$CO($2-1$), $^{13}$CO($2-1$), and C$^{18}$O($2-1$) in 51 Virgo Cluster galaxies with the Atacama Compact Array, part of the Atacama Large Millimeter/submillimeter Array (ALMA). The primary motivation of VERTICO is to understand the physical mechanisms that perturb molecular gas disks, and therefore star formation and galaxy evolution, in dense environments. This first paper contains an overview of VERTICO's design and sample selection, $^{12}$CO($2-1$) observations, and data reduction procedures. We characterize global $^{12}$CO($2-1$) fluxes and molecular gas masses for the 49 detected VERTICO galaxies, provide upper limits for the two non-detections, and produce resolved $^{12}$CO($2-1$) data products (median resolution $= 8^{\prime\prime} \approx 640~{\rm pc}$). Azimuthally averaged $^{12}$CO($2-1$) radial intensity profiles are presented along with derived molecular gas radii. We demonstrate the scientific power of VERTICO by comparing the molecular gas size--mass scaling relation for our galaxies with a control sample of field galaxies, highlighting the strong effect that radius definition has on this correlation. We discuss the drivers of the form and scatter in the size--mass relation and highlight areas for future work. VERTICO is an ideal resource for studying the fate of molecular gas in cluster galaxies and the physics of environment-driven processes that perturb the star formation cycle. Upon public release, the survey will provide a homogeneous legacy dataset for studying galaxy evolution in our closest cluster., 68 pages, 13 Figures, 2 Figure Sets, Accepted for publication in ApJS, Online FITS versions of Tables 1, 2, and 3 are available with the journal publication

Hydrodynamical simulations show that the ram-pressure stripping in galaxy clusters fosters a strong interaction between stripped interstellar medium (ISM) and the surrounding medium, with the possibility of intracluster medium (ICM) cooling into cold gas clouds. Exploiting the MUSE observation of three jellyfish galaxies from the GAs Stripping Phenomena in galaxies with MUSE (GASP) survey, we explore the gas metallicity of star-forming clumps in their gas tails. We find that the oxygen abundance of the stripped gas decreases as a function of the distance from the parent galaxy disk; the observed metallicity profiles indicate that more than 40% of the most metal-poor stripped clouds are constituted by cooled ICM, in qualitative agreement with simulations that predict mixing between the metal-rich ISM and the metal-poor ICM., Accepted for pubblication in ApJL. 9 pages, 4 figures, and 1 table

We investigate the effects of ram pressure on the molecular ISM in the disk of the Coma cluster galaxy NGC 4921, via high resolution CO observations. We present 6" resolution CARMA CO(1-0) observations of the full disk, and 0.4" resolution ALMA CO(2-1) observations of the leading quadrant, where ram pressure is strongest. We find evidence for compression of the dense interstellar medium (ISM) on the leading side, spatially correlated with intense star formation activity in this zone. We also detect molecular gas along kiloparsec-scale filaments of dust extending into the otherwise gas stripped zone of the galaxy, seen in HST images. We find the filaments are connected kinematically as well as spatially to the main gas ridge located downstream, consistent with cloud decoupling inhibited by magnetic binding, and inconsistent with a simulated filament formed via simple ablation. Furthermore, we find several clouds of molecular gas $\sim 1-3$ kpc beyond the main ring of CO that have velocities which are blueshifted by up to 50 km s$^{-1}$ with respect to the rotation curve of the galaxy. These are some of the only clouds we detect that do not have any visible dust extinction associated with them, suggesting that they are located behind the galaxy disk midplane and are falling back towards the galaxy. Simulations have long predicted that some gas removed from the galaxy disk will fall back during ram pressure stripping. This may be the first clear observational evidence of gas re-accretion in a ram pressure stripped galaxy., 27 pages, 14 figures. Accepted for publication in ApJ on July 24, 2021

We study the sensitivity of the z = 0.1 Lyα forest observables, such as the column density distribution function (CDD), flux PDF, flux power spectrum, and line-width distribution, to subgrid models of active galactic nucleus (AGN) feedback using the Illustris and IllustrisTNG (TNG) cosmological simulations. The two simulations share an identical ultraviolet background (UVB) prescription and similar cosmological parameters, but TNG features an entirely reworked AGN feedback model. Due to changes in the AGN radio-mode model, the original Illustris simulations have a factor of 2–3 fewer Lyα absorbers than TNG at column densities N H i < 1015.5 cm−2. We compare the simulated forest statistics to UV data from the Cosmic Origins Spectrograph (COS) and find that neither simulation can reproduce the slope of the absorber distribution. Both Illustris and TNG also produce significantly smaller line-width distributions than observed in the COS data. We show that TNG is in much better agreement with the observed z = 0.1 flux power spectrum than Illustris. We explore which statistics can disentangle the effects of AGN feedback from alternative UVB models by rescaling the UVB of Illustris to produce a CDD match to TNG. While this UVB rescaling is degenerate with the effect of AGN feedback on the CDD, the amplitude and shape of the flux PDF and 1D flux power spectrum change in a way distinct from the scaling of the UVB. Our study suggests that the z = 0.1 Lyα forest observables can be used as a diagnostic of AGN feedback models.

The observed breakBRD ("break bulges in red disks") galaxies are a nearby sample of face-on disk galaxies with particularly centrally concentrated star formation: they have red disks but recent star formation in their centers as measured by the D$_n$4000 spectral index (Tuttle & Tonnesen 2020). In this paper, we search for breakBRD analogues in the IllustrisTNG simulation and describe their history and future. We find that a small fraction (${\sim}4\%$ at $z=0$; ${\sim}1\%$ at $z=0.5$) of galaxies fulfill the breakBRD criteria, in agreement with observations. In comparison with the mass-weighted parent IllustrisTNG sample, these galaxies tend to consist of a higher fraction of satellite and splashback galaxies. However, the central, non-splashback breakBRD galaxies show similar environments, black hole masses, and merger rates, indicating that there is not a single formation trigger for inner star formation and outer quenching. We determine that breakBRD analogue galaxies as a whole are in the process of quenching. The breakBRD state - with its highly centrally concentrated star formation - is uncommon in the history of either currently quiescent or star-forming galaxies; however, approximately 10% of $10^{10} < M_\ast/M_{\odot} < 10^{11}$ quiescent galaxies at $z=0$ have experienced SFR concentrations comparable to those of the breakBRDs in their past. Additionally, the breakBRD state is short-lived, lasting a few hundred Myr up to ${\sim}2$ Gyr. The observed breakBRD galaxies may therefore be a unique sample of outside-in quenching galaxies., Accepted to ApJ

We present HI observations of the jellyfish galaxy, JO201. This massive galaxy (M$_{\ast} = 3.5 \times 10^{10}$ M$_\odot$) is falling along the line-of-sight towards the centre of a rich cluster (M$_{200} \sim 1.6 \times 10^{15}$ M$_\odot$, $\sigma_{cl} \sim 982$ km/s) at a high velocity $\geq$3363 km/s. Its H$\alpha$ emission shows a $\sim$40 kpc tail confined closely to its stellar disc and a $\sim$100 kpc tail extending further out. We find HI emission coinciding only with the shorter clumpy H$\alpha$ tail. In total, we measure an HI mass of M$_{\rm HI} = 1.65 \times 10^{9}$ M$_\odot$, which is about 60% lower than expected based on its stellar mass and stellar surface density. We compared JO201 to another jellyfish in the GASP sample, JO206 (of similar mass but residing in a 10$\times$ less massive cluster), and find that they are similarly HI-deficient. Of the total HI mass in JO201, about 30% lies outside the galaxy disc in projection. This HI fraction is probably a lower limit since most of the HI is redshifted relative to the stellar disc and could be outside the disc. The global star formation rate (SFR) analysis of JO201 suggests that its observed SFR would be expected if it had 10$\times$ its current HI mass. The disc is the main contributor of the high star formation efficiency at a given HI gas density for both galaxies, but their tails also show higher star formation efficiencies compared to the outer regions of field galaxies. Generally, we find that JO201 and JO206 are similar based on their HI content, stellar mass and star formation rate. This finding is unexpected considering their different environments. A toy model comparing the ram pressure of the ICM versus the restoring forces of these galaxies suggests that the ram pressure strength exerted on them could be comparable if we consider their 3D orbital velocities and radial distances relative to the clusters., Comment: 9 pages, 8 figures, Accepted for publication in A&A

The study of the spatially resolved Star Formation Rate-Mass (Sigma_SFR-Sigma_M) relation gives important insights on how galaxies assemble at different spatial scales. Here we present the analysis of the Sigma_SFR-Sigma_M of 40 local cluster galaxies undergoing ram pressure stripping drawn from the GAs Stripping Phenomena in galaxies (GASP) sample. Considering their integrated properties, these galaxies show a SFR enhancement with respect to undisturbed galaxies of similar stellar mass; we now exploit spatially resolved data to investigate the origin and location of the excess. Even on ~1kpc scales, stripping galaxies present a systematic enhancement of Sigma_SFR (~0.35 dex at Sigma_M =108^M_sun/kpc^2) at any given Sigma_M compared to their undisturbed counterparts. The excess is independent on the degree of stripping and of the amount of star formation in the tails and it is visible at all galactocentric distances within the disks, suggesting that the star formation is most likely induced by compression waves from ram pressure. Such excess is larger for less massive galaxies and decreases with increasing mass. As stripping galaxies are characterised by ionised gas beyond the stellar disk, we also investigate the properties of 411 star forming clumps found in the galaxy tails. At any given stellar mass density, these clumps are systematically forming stars at a higher rate than in the disk, but differences are reconciled when we just consider the mass formed in the last few 10^8yr ago, suggesting that on these timescales the local mode of star formation is similar in the tails and in the disks., 20 pages, 13 figures, accepted for publication in ApJ

We examine the properties of the circumgalactic medium (CGM) at low redshift in a range of simulated Milky Way mass halos. The sample is comprised of seven idealized simulations, an adaptive mesh refinement cosmological zoom-in simulation, and two groups of 50 halos with star forming or quiescent galaxies taken from the IllustrisTNG100 simulation. The simulations have very different setups, resolution, and feedback models, but are analyzed in a uniform manner. By comparing median radial profiles and mass distributions of CGM properties, we isolate key similarities and differences. In doing so, we advance the efforts of the SMAUG (Simulating Multiscale Astrophysics to Understand Galaxies) project that aims to understand the inherently multiscale galaxy formation process. In the cosmological simulations, the CGM exhibits nearly flat temperature distributions, and broad pressure and radial velocity distributions. In the idealized simulations, similar distributions are found in the inner CGM ($\lesssim 0.5 \, r_{\rm 200c}$) when strong galactic feedback models are employed, but the outer CGM ($\gtrsim 0.5 \, r_{\rm 200c}$) has a much less prominent cold phase, and narrower pressure and velocity distributions even in models with strong feedback. This comparative analysis demonstrates the dominant role feedback plays in shaping the inner CGM and the increased importance of cosmological effects, such as nonspherical accretion and satellite galaxies, in the outer CGM. Furthermore, our findings highlight that while cosmological simulations are required to capture the multiphase structure of the CGM at large radii, idealized simulations provide a robust framework to study how galactic feedback interacts with the inner CGM and thereby provide a reliable avenue to constrain feedback prescriptions., Comment: More information on the SMAUG project and the other first result papers can be found here: https://www.simonsfoundation.org/flatiron/center-for-computational-astrophysics/galaxy-formation/smaug/papersplash1

Semi-analytic models (SAMs) are a promising means of tracking the physical processes associated with galaxy formation, but many of their approximations have not been rigorously tested. As part of the SMAUG (Simulating Multiscale Astrophysics to Understand Galaxies) project, we compare predictions from the FIRE-2 hydrodynamical "zoom-in" simulations to those from the Santa Cruz SAM run on the same halo merger trees, with an emphasis on the global mass flow cycle. Our study includes 13 halos spanning low-mass dwarfs (M_vir~10^10 M_sun at z=0), intermediate-mass dwarfs (M_vir~10^11 M_sun) and Milky Way-mass galaxies (M_vir~10^12 M_sun). The SAM and FIRE-2 predictions agree relatively well with each other in terms of stellar and interstellar mass, but differ dramatically on circumgalactic mass (the SAM is lower than FIRE-2 by ~3 orders of magnitude for dwarfs). Strikingly, the SAM predicts higher gas accretion rates for dwarfs compared to FIRE-2 by factors of ~10-100, and this is compensated for with higher mass outflow rates in the SAM. We argue that the most severe model discrepancies are caused by the lack of preventative stellar feedback and the assumptions for halo gas cooling and recycling in the SAM. As a first step towards resolving these model tensions, we present a simple yet promising new preventative stellar feedback model in which the energy carried by supernova-driven winds is allowed to heat some fraction of gas outside of halos to at least the virial temperature such that accretion is suppressed., Comment: Accepted to ApJ with minor revisions. More information on the SMAUG project and the other first result papers can be found here: https://www.simonsfoundation.org/flatiron/center-for-computational-astrophysics/galaxy-formation/smaug/papersplash1

Using MUSE observations from the GASP survey, we study 54 galaxies undergoing ram-pressure stripping (RPS) spanning a wide range in galaxy mass and host cluster mass. We use this rich sample to study how the star formation rate (SFR) in the tails of stripped gas depends on the properties of the galaxy and its host cluster. We show that the interplay between all the parameters involved is complex and that there is not a single, dominant one in shaping the observed amount of SFR. Hence, we develop a simple analytical approach to describe the mass fraction of stripped gas and the SFR in the tail, as a function of the cluster velocity dispersion, galaxy stellar mass, clustercentric distance and speed in the intracluster medium. Our model provides a good description of the observed gas truncation radius and of the fraction of star-formation rate (SFR) observed in the stripped tails, once we take into account the fact that the star formation efficiency in the tails is a factor $\sim 5$ lower than in the galaxy disc, in agreement with GASP ongoing HI and CO observations. We finally estimate the contribution of RPS to the intracluster light (ICL) and find that the average SFR in the tails of ram-pressure stripped gas is $\sim 0.22 M_{\odot}\,\mathrm{yr}^{-1} $ per cluster. By extrapolating this result to evaluate the contribution to the ICL at different epochs, we compute an integrated average value per cluster of $\sim 4 \times 10^9 M_\odot$ of stars formed in the tails of RPS galaxies since $z\sim 1$., Comment: Accepted for publication in ApJ

Based on MUSE data from the GASP survey, we study the Halpha-emitting extraplanar tails of 16 cluster galaxies at z~0.05 undergoing ram pressure stripping. We demonstrate that the dominating ionization mechanism of this gas (between 64% and 94% of the Halpha emission in the tails depending on the diagnostic diagram used) is photoionization by young massive stars due to ongoing star formation (SF) taking place in the stripped tails. This SF occurs in dynamically quite cold HII clumps with a median Halpha velocity dispersion sigma = 27 km s^-1. We study the characteristics of over 500 star-forming clumps in the tails and find median values of Halpha luminosity L_{Halpha} = 4 X 10^38 erg s^-1, dust extinction A_V=0.5 mag, star formation rate SFR=0.003 M_sun yr^-1, ionized gas density n_e =52 cm^-3, ionized gas mass M_gas = 4 X 10^4 Msun, and stellar mass M_{*} = 3 X 10^6 Msun. The tail clumps follow scaling relations (M_gas-M_{*}, L_{Halpha} -sigma, SFR-M_gas) similar to disk clumps, and their stellar masses are comparable to Ultra Compact Dwarfs and Globular Clusters.The diffuse gas component in the tails is ionized by a combination of SF and composite/LINER-like emission likely due to thermal conduction or turbulence. The stellar photoionization component of the diffuse gas can be due either to leakage of ionizing photons from the HII clumps with an average escape fraction of 18%, or lower luminosity HII regions that we cannot individually identify., Comment: accepted for publication in MNRAS

We introduce a collection of primarily centrally star-forming galaxies that are selected by disk color to have truncated disk star formation. We show that common explanations for centrally concentrated star formation—low stellar mass, bars, and high-density environments—do not universally apply to this sample. To gain insight into our sample, we compare these galaxies to a parent sample of strongly star-forming galaxies and to a parent sample of galaxies with low specific star formation rates. We find that in star formation and color space from ultraviolet to the infrared these galaxies either fall between the two samples or agree more closely with galaxies with high specific star formation rates. Their morphological characteristics also lie between high and low specific star formation rate galaxies, although their Petrosian radii agree well with that of the low specific star formation rate parent sample. We discuss whether this sample is likely to be quenching or showing an unusual star formation distribution while continuing to grow through star formation. Future detailed studies of these galaxies will give us insights into how the local conditions within a galaxy balance environmental influence to govern the distribution of star formation. In this first paper in a series, we describe the global properties that identify this sample as separate from more average spiral galaxies, and we identify paths forward to explore the underlying causes of their differences.

The simplest scheme for predicting real galaxy properties after performing a dark matter simulation is to rank order the real systems by stellar mass and the simulated systems by halo mass and then simply assume monotonicity - that the more massive halos host the more massive galaxies. This has had some success, but we study here if a better motivated and more accurate matching scheme is easily constructed by looking carefully at how well one could predict the simulated IllustrisTNG galaxy sample from its dark matter computations. We find that using the dark matter rotation curve peak velocity, $v_{max}$, for normal galaxies reduces the error of the prediction by 30% (18% for central galaxies and 60% for satellite systems) - following expectations from Faber-Jackson and the physics of monolithic collapse. For massive systems with halo mass $>$ 10$^{12.5}$ M$_{\odot}$ hierarchical merger driven formation is the better model and dark matter halo mass remains the best single metric. Using a new single variable that combines these effects, $\phi$ $=$ $v_{max}$/$v_{max,12.7}$ + M$_{peak}$/(10$^{12.7}$ M$_{\odot}$) allows further improvement and reduces the error, as compared to ranking by dark matter mass at $z=0$ by another 6% from $v_{max}$ ranking. Two parameter fits -- including environmental effects produce only minimal further impact.

We present VLA HI observations of JO206, a prototypical ram-pressure stripped galaxy in the GASP sample. This massive galaxy (M$_{\ast} =$ 8.5 $\times$ 10$^{10}$ M$_{\odot}$) is located at a redshift of $z =$ 0.0513, near the centre of the low-mass galaxy cluster, IIZw108 ($\sigma \sim575$ km/s). JO206 is characterised by a long tail ($\geq$90 kpc) of ionised gas stripped away by ram-pressure. We find a similarly long HI tail in the same direction as the ionised gas tail and measure a total HI mass of $3.2 \times 10^{9}$ M$_{\odot}$. This is about half the expected HI mass given the stellar mass and surface density of JO206. A total of $1.8 \times 10^{9}$ M$_{\odot}$ (60%) of the detected HI is in the gas stripped tail. An analysis of the star formation rate shows that the galaxy is forming more stars compared to galaxies with the same stellar and HI mass. On average we find a HI gas depletion time of $\sim$0.5 Gyr which is about four times shorter than that of "normal" spiral galaxies. We performed a spatially resolved analysis of the relation between star formation rate density and gas density in the disc and tail of the galaxy at the resolution of our HI data. The star formation efficiency of the disc is about 10 times higher than that of the tail at fixed HI surface densities. Both the inner and outer parts of JO206 show an enhanced star formation compared to regions of similar HI surface density in field galaxies. The enhanced star formation is due to ram-pressure stripping during the galaxy's first infall into the cluster., Comment: 13 pages, 12 figures, Accepted for publication in MNRAS

We investigate the importance of varying the ram pressure to more realistically mimic the infall of a cluster satellite galaxy when comparing ram pressure stripping simulations to observations. We examine the gas disk and tail properties of stripped cluster galaxies in eight "wind-tunnel" hydrodynamical simulations with either varying or constant ram pressure strength. In simulations without radiative cooling, applying a varying wind leads to significantly different density and velocity structure in the tail than found when applying a constant wind, although the stripping rate, disk mass, and disk radius remain consistent in both scenarios. In simulations with radiative cooling, the differences between a constant and varying wind are even more pronounced. Not only is there a difference in morphology and velocity structure in the tails, but a varying wind leads to a much lower stripping rate, even after the varying wind has reached the ram pressure strength of the constant wind. Also, galaxies in constant and varying wind simulations with the same gas disk mass do not have in the same gas disk radius. A constant wind cannot appropriately model the ram pressure stripping of a galaxy entering a cluster. We conclude that simulations attempting detailed comparisons with observations must take the variation of the ram pressure profile due to a galaxy's orbit into consideration., Accepted in ApJ

We present a study of the physical properties of JO201, a unique disk galaxy with extended tails undergoing extreme ram-pressure stripping as it moves through the massive cluster Abell 85 at supersonic speeds mostly along the line of sight. JO201 was observed with MUSE as part of the GASP programme. In a previous paper (GASP II) we studied the stellar and gas kinematics. In this paper we present emission-line ratios, gas-phase metallicities and ages of the stellar populations across the galaxy disk and tails. We find that while the emission at the core of the galaxy is dominated by an active galactic nucleus (AGN), the disk is composed of star-forming knots surrounded by excited diffuse gas. The collection of star-forming knots presents a metallicity gradient steadily decreasing from the centre of the galaxy outwards, and the ages of the stars across the galaxy show that the tails formed, 17 pages, 12 figures

Exploiting the sample of 30 local star-forming, undisturbed late-type galaxies in different environments drawn from the GAs Stripping Phenomena in galaxies with MUSE (GASP), we investigate the spatially resolved Star Formation Rate-Mass ({\Sigma}SFR-{\Sigma}_star) relation. Our analysis includes also the galaxy outskirts (up to >4 effective radii, re), a regime poorly explored by other Integral Field Spectrograph surveys. Our observational strategy allows us to detect H{\alpha} out to more than 2.7re for 75% of the sample. Considering all galaxies together, the correlation between the {\Sigma}SFR and {\Sigma}_star is quite broad, with a scatter of 0.3 dex. It gets steeper and shifts to higher {\Sigma}_star values when external spaxels are excluded and moving from less to more massive galaxies. The broadness of the overall relation suggests galaxy-by-galaxy variations. Indeed, each object is characterized by a distinct {\Sigma}SFR-{\Sigma}_star relation and in some cases the correlation is very loose. The scatter of the relation mainly arises from the existence of bright off-center star-forming knots whose {\Sigma}SFR-{\Sigma}_star relation is systematically broader than that of the diffuse component. The {\Sigma}SFR-{\Sigma}tot gas (total gas surface density) relation is as broad as the {\Sigma}SFR-{\Sigma}_star relation, indicating that the surface gas density is not a primary driver of the relation. Even though a large galaxy-by-galaxy variation exists, mean {\Sigma}SFR and {\Sigma}_star values vary of at most 0.7 dex across galaxies. We investigate the relationship between the local and global SFR-M_star relation, finding that the latter is driven by the existence of the size-mass relation., Comment: MNRAS in press, 19 pages, 14 figures

Feedback is indispensable in galaxy formation. However, lacking resolutions, cosmological simulations often use ad hoc feedback parameters. Conversely, small-box simulations, while better resolving the feedback, cannot capture gas evolution beyond the simulation domain. We aim to bridge the gap by implementing small-box results of supernovae-driven outflows into dark matter halo-scale simulations and studying their impact on large scales. Galactic outflows are multiphase, but small-box simulations show that the hot phase (T$\approx$ 10$^{6-7}$ K) carries the majority of energy and metals. We implement hot outflows in idealized simulations of the Milky Way halo, and examine how they impact the circumgalactic medium (CGM). In this paper, we discuss the case when the star formation surface density is low and therefore the emerging hot outflows are gravitationally bound by the halo. We find that outflows form a large-scale, metal-enriched atmosphere with fountain motions. As hot gas accumulates, the inner atmosphere becomes "saturated". Cool gas condenses, with a rate balancing the injection of the hot outflows. This balance leads to a universal density profile of the hot atmosphere, independent of mass outflow rate. The atmosphere has a radially-decreasing temperature, naturally producing the observed X-ray luminosity and column densities of O VI, O VII, O VIII. The self-regulated atmosphere has a baryon and a metal mass of $(0.5-1.2)\times 10^{10}M_\odot$ and $(0.6-1.4)\times 10^8 M_\odot$, respectively, small compared to the ``missing" baryons and metals from the halo. We conjecture that the missing materials reside at even larger radii, ejected by more powerful outflows in the past., Comment: 26 pages, 18 figures, accepted by ApJ

It is well known that galaxies falling into clusters can experience gas stripping due to ram-pressure by the intra-cluster medium (ICM). The most spectacular examples are galaxies with extended tails of optically-bright stripped material known as "jellyfish". We use the first large homogeneous compilation of jellyfish galaxies in clusters from the WINGS and OmegaWINGS surveys, and follow-up MUSE observations from the GASP MUSE programme to investigate the orbital histories of jellyfish galaxies in clusters and reconstruct their stripping history through position vs. velocity phase- space diagrams. We construct analytic models to define the regions in phase-space where ram-pressure stripping is at play. We then study the distribution of cluster galaxies in phase-space and find that jellyfish galaxies have on average higher peculiar velocities (and higher cluster velocity dispersion) than the overall population of cluster galaxies at all clustercentric radii, which is indicative of recent infall into the cluster and radial orbits. In particular, the jellyfish galaxies with the longest gas tails reside very near the cluster cores (in projection) and are moving at very high speeds, which coincides with the conditions of the most intense ram-pressure. We conclude that many of the jellyfish galaxies seen in clusters likely formed via fast (~1- 2 Gyr), incremental, outside-in ram-pressure stripping during first infall into the cluster in highly radial orbits., Comment: 14 pages, 9 figures, MNRAS in press

GAs Stripping Phenomena in galaxies with MUSE (GASP) is a program aimed at studying gas removal processes in nearby galaxies in different environments. We present the study of four galaxies that are part of the same group (z= 0.06359) and highlight the multitude of mechanisms affecting the spatially resolved properties of the group members. One galaxy is passive and shows a regular stellar kinematics. The analysis of its star formation history indicates that the quenching process lasted for a few Gyr and that the star formation declined throughout the disk in a similar way, consistent with strangulation. Another galaxy is characterised by a two-component stellar disk with an extended gas disk that formed a few 10^8 yr ago, most likely as a consequence of gas accretion. The third member is a spiral galaxy at the edges of the group, but embedded in a filament. We hypothesise that the compression exerted by the sparse intergalactic medium on the dense circumgalactic gas switches on star formation in a number of clouds surrounding the galaxy ("cosmic web enhancement"). Alternatively, also ram pressure stripping might be effective. Finally, the fourth galaxy is a spiral with a truncated ionised gas disk and an undisturbed stellar kinematics. An analytical model of the galaxy's restoring pressure, and its location and velocity within the cluster, suggest ram pressure is the most likely physical mechanism in action. This is the first optical evidence for stripping in groups., Comment: 19 page, 12 figures

The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band Halpha+[NII] imaging survey carried out with MegaCam at the Canada-France-Hawaii Telescope. The survey covers the whole Virgo cluster region from its core to one virial radius (104 deg^2). The sensitivity of the survey is of f(Halpha) ~ 4 x 10^-17 erg sec-1 cm^-2 (5 sigma detection limit) for point sources and Sigma (Halpha) ~ 2 x 10^-18 erg sec^-1 cm^-2 arcsec^-2 (1 sigma detection limit at 3 arcsec resolution) for extended sources, making VESTIGE the deepest and largest blind narrow-band survey of a nearby cluster. This paper presents the survey in all its technical aspects, including the survey design, the observing strategy, the achieved sensitivity in both the narrow-band Halpha+[NII] and in the broad-band r filter used for the stellar continuum subtraction, the data reduction, calibration, and products, as well as its status after the first observing semester. We briefly describe the Halpha properties of galaxies located in a 4x1 deg^2 strip in the core of the cluster north of M87, where several extended tails of ionised gas are detected. This paper also lists the main scientific motivations of VESTIGE, which include the study of the effects of the environment on galaxy evolution, the fate of the stripped gas in cluster objects, the star formation process in nearby galaxies of different type and stellar mass, the determination of the Halpha luminosity function and of the Halpha scaling relations down to ~ 10^6 Mo stellar mass objects, and the reconstruction of the dynamical structure of the Virgo cluster. This unique set of data will also be used to study the HII luminosity function in hundreds of galaxies, the diffuse Halpha+[NII] emission of the Milky Way at high Galactic latitude, and the properties of emission line galaxies at high redshift., Accepted for publication on Astronomy & Astrophysics

Exploiting the data from the GAs Stripping Phenomena in galaxies with MUSE (GASP) program, we compare the integrated Star Formation Rate- Mass relation (SFR-M_ast) relation of 42 cluster galaxies undergoing ram pressure stripping ("stripping galaxies") to that of 32 field and cluster undisturbed galaxies. Theoretical predictions have so far led to contradictory conclusions about whether ram pressure can enhance the star formation in the gas disks and tails or not and until now a statistically significant observed sample of stripping galaxies was lacking. We find that stripping galaxies occupy the upper envelope of the control sample SFR-M_ast relation, showing a systematic enhancement of the SFR at any given mass. The star formation enhancement occurs in the disk (0.2 dex), and additional star formation takes place in the tails. Our results suggest that strong ram pressure stripping events can moderately enhance the star formation also in the disk prior to gas removal., Comment: ApJL in press

When supermassive black holes at the center of galaxies accrete matter (usually gas), they give rise to highly energetic phenomena named Active Galactic Nuclei (AGN). A number of physical processes have been proposed to account for the funneling of gas towards the galaxy centers to feed the AGN. There are also several physical processes that can strip gas from a galaxy, and one of them is ram pressure stripping in galaxy clusters due to the hot and dense gas filling the space between galaxies. We report the discovery of a strong connection between severe ram pressure stripping and the presence of AGN activity. Searching in galaxy clusters at low redshift, we have selected the most extreme examples of jellyfish galaxies, which are galaxies with long tentacles of material extending for dozens of kpc beyond the galaxy disk. Using the MUSE spectrograph on the ESO Very Large Telescope, we find that 6 out of the 7 galaxies of this sample host a central AGN, and two of them also have galactic-scale AGN ionization cones. The high incidence of AGN among the most striking jellyfishes may be due to ram pressure causing gas to flow towards the center and triggering the AGN activity, or to an enhancement of the stripping caused by AGN energy injection, or both. Our analysis of the galaxy position and velocity relative to the cluster strongly supports the first hypothesis, and puts forward ram pressure as another, yet unforeseen, possible mechanism for feeding the central supermassive black hole with gas., published in Nature, Vol.548, Number 7667, pag.304

We present 12CO (2-1) data of three Virgo spirals - NGC 4330, NGC 4402 and NGC 4522 obtained using the Submillimeter Array. These three galaxies show clear evidence of ram pressure stripping due to the cluster medium as found in previous HI imaging studies. Using high-resolution CO data, we investigate how the properties of the inner molecular gas disc change while a galaxy is undergoing HI stripping in the cluster. At given sensitivity limits, we do not find any clear signs of molecular gas stripping. However, both its morphology and kinematics appear to be quite disturbed as those of HI. Morphological peculiarities present in the molecular and atomic gas are closely related with each other, suggesting that molecular gas can be also affected by strong ICM pressure even if it is not stripped. CO is found to be modestly enhanced along the upstream sides in these galaxies, which may change the local star formation activity in the disc. Indeed, the distribution of H$\alpha$ emission, a tracer of recent star formation, well coincides with that of the molecular gas, revealing enhancements near the local CO peak or along the CO compression. FUV and H$\alpha$ share some properties in common, but FUV is always more extended than CO/H$\alpha$ in the three galaxies, implying that the star-forming disc is rapidly shrinking as the molecular gas properties have changed. We discuss how ICM pressure affects dense molecular gas and hence star formation properties while diffuse atomic gas is being removed from a galaxy., Comment: 18 pages, 10 figures, 4 tables, accepted for publication in MNRAS; high resolution figures available at http://mnras.oxfordjournals.org/content/early/2016/12/07/mnras.stw3162.full.pdf+html

In spatially resolved galaxy observations, star formation rate radial profiles are found to correlate with total specific star formation rates. A central depletion in star formation is thought to correlate with the globally depressed star formation rates of, for example, galaxies within the Green Valley. We present, for the first time, radial specific star formation rate profiles for a statistical sample of simulated galaxies from the Illustris and EAGLE large cosmological simulations. For galaxies on the star-forming sequence, simulated specific star formation rate profiles are in loose agreement with observations, although galaxies from the EAGLE simulation are too centrally peaked, and galaxies from Illustris have a steeper decline at large radii. However, both galaxy samples show centrally concentrated star formation for galaxies in the Green Valley at all galaxy stellar masses, indicating that quenching occurs from the outside-in, in strong conflict with observations of inside-out quenching. These results appear in spite of the different feedback models in these two simulations. We conclude that the distribution of star formation within galaxies is a strong additional constraint for star formation and feedback models in simulations, in particular related to the quenching of star formation., Comment: ApJL accepted

Many properties of the Milky Way's dark matter halo, including its mass assembly history, concentration, and subhalo population, remain poorly constrained. We explore the connection between these properties of the Milky Way and its satellite galaxy population, especially the implication of the presence of the Magellanic Clouds for the properties of the Milky Way halo. Using a suite of high-resolution $N$-body simulations of Milky Way-mass halos with a fixed final Mvir ~ 10^{12.1}Msun, we find that the presence of Magellanic Cloud-like satellites strongly correlates with the assembly history, concentration, and subhalo population of the host halo, such that Milky Way-mass systems with Magellanic Clouds have lower concentration, more rapid recent accretion, and more massive subhalos than typical halos of the same mass. Using a flexible semi-analytic galaxy formation model that is tuned to reproduce the stellar mass function of the classical dwarf galaxies of the Milky Way with Markov-Chain Monte-Carlo, we show that adopting host halos with different mass-assembly histories and concentrations can lead to different best-fit models for galaxy-formation physics, especially for the strength of feedback. These biases arise because the presence of the Magellanic Clouds boosts the overall population of high-mass subhalos, thus requiring a different stellar-mass-to-halo-mass ratio to match the data. These biases also lead to significant differences in the mass--metallicity relation, the kinematics of low-mass satellites, the number counts of small satellites associated with the Magellanic Clouds, and the stellar mass of Milky Way itself. Observations of these galaxy properties can thus provide useful constraints on the properties of the Milky Way halo., Comment: 20 pages, 12 figures, accepted for publication in ApJ. A new section on the effect of host halo mass-assembly history on the central galaxy stellar mass is added