We present a joint shear-and-magnification weak-lensing analysis of a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters at 0.19 < ∼ z < ∼ 0.69 selected from the Cluster Lensing And Supernova survey with Hubble (CLASH). Our analysis uses wide-field multi-color imaging, taken primarily with Suprime-Cam on the Subaru Telescope. From a stacked shear-only analysis of the X-ray-selected subsample, we detect the ensemble-averaged lensing signal with a total signal-to-noise ratio of 25 in the radial range of 200 to 3500 kpc h −1 , providing integrated constraints on the halo profile shape and concentration-mass relation. The stacked tangential-shear signal is well described by a family of standard density profiles predicted for dark-matter-dominated halos in gravitational equilibrium, namely the Navarro-Frenk-White (NFW), truncated variants of NFW, and Einasto models. For the NFW model, we measure a mean concentration of c 200c = 4.01 +0.35 −0.32 at an effective halo mass of M 200c = 1.34 +0.10 −0.09 × 10 15 M . We show this is in excellent agreement with Λ cold-dark-matter (ΛCDM) predictions when the CLASH X-ray selection function and projection effects are taken into account. The best-fit Einasto shape parameter is α E = 0.191 +0.071 −0.068 , which is consistent with the NFWequivalent Einasto parameter of ∼ 0.18. We reconstruct projected mass density profiles of all CLASH clusters from a joint likelihood analysis of shear-and-magnification data, and measure cluster masses at several characteristic radii assuming an NFW density profile. We also derive an ensemble-averaged total projected mass profile of the X-ray-selected subsample by stacking their individual mass profiles. The stacked total mass profile, constrained by the shear+magnification data, is shown to be consistent with our shear-based halo-model predictions including the effects of surrounding large-scale structure as a two-halo term, establishing further consistency in the context of the ΛCDM model.

We present results from a comprehensive lensing analysis in HST data, of the complete Cluster Lensing And Supernova survey with Hubble (CLASH) cluster sample. We identify new multiple-images previously undiscovered, allowing improved or first constraints on the cluster inner mass distributions and profiles. We combine these strong-lensing constraints with weak-lensing shape measurements within the HST FOV to jointly constrain the mass distributions. The analysis is performed in two different common parameterizations (one adopts light-traces-mass for both galaxies and dark matter while the other adopts an analytical, elliptical NFW form for the dark matter), to provide a better assessment of the underlying systematics -which is most important for deep, cluster-lensing surveys, especially when studying magnified high-redshift objects. We find that the typical (median), relative systematic differences throughout the central FOV are ∼ 40% in the (dimensionless) mass density, κ, and ∼ 20% in the magnification, µ. We show maps of these differences for each cluster, as well as the mass distributions, critical curves, and 2D integrated mass profiles. For the Einstein radii (z s = 2) we find that all typically agree within 10% between the two models, and Einstein masses agree, typically, within ∼ 15%. At larger radii, the total projected, 2D integrated mass profiles of the two models, within r ∼ 2 , differ by ∼ 30%. Stacking the surface-density profiles of the sample from the two methods together, we obtain an average slope of d log(Σ)/d log(r) ∼ −0.64 ± 0.1, in the radial range [5,350] kpc. Lastly, we also characterize the behavior of the average magnification, surface density, and shear differences between the two models, as a function of both the radius from the center, and the best-fit values of these quantities. All mass models and magnification maps are made publicly available for the community.

GASP (GAs Stripping Phenomena in galaxies with MUSE) is a new integral-field spectroscopic survey with MUSE at the VLT aiming at studying gas removal processes in galaxies. We present an overview of the survey and show a first example of a galaxy undergoing strong gas stripping. GASP is obtaining deep MUSE data for 114 galaxies at z=0.04-0.07 with stellar masses in the range 10 9.2 -10 11.5 M in different environments (galaxy clusters and groups, over more than four orders of magnitude in halo mass). GASP targets galaxies with optical signatures of unilateral debris or tails reminiscent of gas stripping processes ("jellyfish galaxies"), as well as a control sample of disk galaxies with no morphological anomalies. GASP is the only existing Integral Field Unit (IFU) survey covering both the main galaxy body and the outskirts and surroundings, where the IFU data can reveal the presence and the origin of the outer gas. To demonstrate GASP's ability to probe the physics of gas and stars, we show the complete analysis of a textbook case of a "jellyfish" galaxy, JO206. This is a massive galaxy (9 × 10 10 M ) in a low-mass cluster (σ ∼ 500 km s −1 ), at a small projected clustercentric radius and a high relative velocity, with ≥90kpc-long tentacles of ionized gas stripped away by ram pressure. We present the spatially resolved kinematics and physical properties of gas and stars, and depict the evolutionary history of this galaxy.

We present a new multiwavelength analysis of the Coma cluster subclustering based on recent X-ray data and on a compilation of nearly 900 redshifts. We characterize subclustering using the Serna & Gerbal (1996, A&A, 309, 65) hierarchical method, which makes use of galaxy positions, redshifts, and magnitudes, and identify 17 groups. One of these groups corresponds to the main cluster, one is the well known group associated with the infalling galaxy NGC 4839, and one is associated with NGC 4911/NGC 4926. About one third of the 17 groups have velocity distributions centered on the velocities of the very bright cluster galaxies they contain (magnitudes R < 13). In order to search for additional substructures, we made use of the isophotes of X-ray brightness residuals left after the subtraction of the best-fit β-model from the overall X-ray gas distribution (Neumann et al. 2003, A&A, 400, 811). We selected galaxies within each of these isophotes and compared their velocity distributions with that of the whole cluster. We confirm in this way the two groups associated, respectively, with NGC 4839, and with the southern part of the extended western substructure visible in X-rays. We discuss the group properties in the context of a scenario in which Coma is built by the accretion of groups infalling from the surrounding large-scale structure. We estimate the recent mass accretion rate of Coma and compare it with hierarchical models of cluster evolution.

We present an analysis of the relation between the masses of cluster-and group-sized halos, extracted from ΛCDM cosmological N-body and hydrodynamic simulations, and their velocity dispersions, at different redshifts from z = 2 to z = 0. The main aim of this analysis is to understand how the implementation of baryonic physics in simulations affects such relation, i.e. to what extent the use of the velocity dispersion as a proxy for cluster mass determination is hampered by the imperfect knowledge of the baryonic physics. In our analysis we use several sets of simulations with different physics implemented: one DM-only simulation, one simulation with non-radiative gas, and two radiative simulations, one of which with feedback from Active Galactic Nuclei. Velocity dispersions are determined using three different tracers, dark matter (DM hereafter) particles, subhalos, and galaxies.We confirm that DM particles trace a relation that is fully consistent with the theoretical expectations based on the virial theorem, σ v ∝ M α with α = 1/3, and with previous results presented in the literature. On the other hand, subhalos and galaxies trace steeper relations, with velocity dispersion scaling with mass with α > 1/3, and with larger values of the normalization. Such relations imply that galaxies and subhalos have a ∼ 10 per cent velocity bias relative to the DM particles, which can be either positive or negative, depending on halo mass, redshift and physics implemented in the simulation.We explain these differences as due to dynamical processes, namely dynamical friction and tidal disruption, acting on substructures and galaxies, but not on DM particles. These processes appear to be more or less effective, depending on the halo masses and the importance of baryon cooling, and may create a non-trivial dependence of the velocity bias and the σ 1D -M 200 relation on the tracer, the halo mass and its redshift.These results are relevant in view of the application of velocity dispersion as a proxy for cluster masses in ongoing and future large redshift surveys.

Aims. We study the efficiency and reliability of cluster mass estimators that are based on the projected phase-space distribution of galaxies in a cluster region. Methods. We analyse a data-set of 62 clusters extracted from a concordance ΛCDM cosmological hydrodynamical simulation. We consider both dark matter (DM) particles and simulated galaxies as tracers of the clusters gravitational potential. Two cluster mass estimators are considered: the virial mass estimator, corrected for the surface-pressure term, and a mass estimator (that we call M σ ) based entirely on the velocity dispersion estimate of the cluster. In order to simulate observations, galaxies (or DM particles) are first selected in cylinders of given radius (from 0.5 to 1.5h −1 Mpc) and 200h −1 Mpc length. Cluster members are then identified by applying a suitable interloper removal algorithm. Results. The virial mass estimator overestimates the true mass by 10% on average, for sample sizes of > ∼ 60 cluster members. For similar sample sizes, M σ underestimates the true mass by 15%, on average. For smaller sample sizes, the bias of the virial mass estimator substantially increases, while the M σ estimator becomes essentially unbiased. The dispersion of both mass estimates increases by a factor ∼2 as the number of cluster members decreases from ∼400 to ∼20. It is possible to reduce the bias in the virial mass estimates either by removing clusters with significant evidence for subclustering or by selecting early-type galaxies, which substantially reduces the interloper contamination. Early-type galaxies cannot however be used to improve the M σ estimates since their intrinsic velocity distribution is slightly biased relative to that of the DM particles. Radially-dependent incompleteness can drastically affect the virial mass estimates, but leaves the M σ estimates almost unaffected. Other observational effects, like centering and velocity errors and different observational apertures, have little effect on the mass estimates.

We analyze the Luminosity Functions (LFs) of a subsample of 69 clusters from the RASS-SDSS galaxy cluster catalog. When calculated within the cluster physical sizes, given by r 200 or r 500 , all the cluster LFs appear to have the same shape, well fitted by a composite of two Schechter functions with a marked upturn and a steepening at the faint-end. Previously reported cluster-to-cluster variations of the LF faint-end slope are due to the use of a metric cluster aperture for computing the LF of clusters of different masses. We determine the composite LF for early-and late-type galaxies, where the typing is based on the galaxy u − r colors. The late-type LF is well fitted by a single Schechter function with a steep slope (α = −2.0 in the r band, within r 200 ). The early-type LF instead cannot be fitted by a single Schechter function, and a composite of two Schechter functions is needed. The faint-end upturn of the global cluster LF is due to the early-type cluster galaxies. The shape of the bright-end tail of the early-type LF does not seem to depend upon the local galaxy density or the distance from the cluster center. The late-type LF shows a significant variation only very near the cluster center. On the other hand, the faint-end tail of the early-type LF shows a significant and continuous variation with the environment. We provide evidence that the process responsible for creating the excess population of dwarf early type galaxies in clusters is a threshold process that occurs when the density exceeds ∼500 times the critical density of the Universe. We interpret our results in the context of the "harassment" scenario, where faint early-type cluster galaxies are predicted to be the descendants of tidally-stripped late-type galaxies.

We present the results of a numerical study based on the analysis of the MUSIC-2 N-body/hydrodynamical 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 linesof-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 unrelaxed systems. For such a heterogeneous 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.