CLASH-VLT velocity anisotropy profiles in a stack of massive galaxy clusters

Clusters of galaxies represent the largest laboratories in the universe for testing the incredibly chaotic physics governing the collapse of baryons into the stars, galaxies, groups, and diffuse clouds that we see today. Within the cluster environment, there are a wide variety of physical processes that may be acting to transform galaxies. In this thesis, we combine extensive Keck spectroscopy with wide-field HST imaging to perform a detailed case study of two intermediate redshift galaxy clusters, Cl 0024+1654 (z=0.395) and MS 0451-03 (z=0.540). Leveraging a comprehensive multiwavelength data set that spans the X-ray to infrared, and with spectral-line measurements serving as the key to revealing both the recent star-formation histories and kinematics of infalling galaxies, we aim to shed light on the environmental processes that could be acting to transform galaxies in clusters. We adopt a strategy to make maximal use of our HST-based morphologies by splitting our sample of cluster galaxies according to morphological type, characterizing signs of recent evolution in and early types separately. This approach proves to be powerful in identifying galaxies that are currently being altered by an environmental interaction: early-type galaxies that have either been newly transformed or prodded back into an active phase, and spiral galaxies where star formation is being suppressed or enhanced all stand out in our sample. We begin by using variations in the early-type galaxy population as indicators of recent activity. Because ellipticals and S0s form such a homogeneous class in the local universe, we are sensitive to even very subtle signatures of recent and current environmental interactions. This study has yielded two key results: By constructing the Fundamental Plane (FP) of Cl 0024, we observe that elliptical and S0 galaxies exhibit a high scatter in their FP residuals, which occurs only among galaxies in the cluster core, suggesting a turbulent assembly history for Cl 0024 early types. Near the Virial radius of Cl 0024, we observe a number of compact, intermediate-mass ellipticals undergoing a burst of star formation or weak AGN activity, indicated by strong [O II] emission; their locations may mark the minimum radius at which merging is effective in each cluster. While E+S0 galaxies do prove to be sensitive indicators of environmental interaction, it is the spiral galaxies that, of course, host the bulk of star formation within and around these clusters. We therefore probe for kinematic disturbances in spiral disks by measuring resolved rotation curves from optical emission lines, and constructing the Tully-Fisher relation for across Cl 0024 and MS 0451. We find that the cluster Tully-Fisher relation exhibits significantly higher scatter than the field relation. In probing for the origin of this difference, we find that the central mass densities of star-forming exhibit a sharp break near the cluster Virial radius, with in the cluster outskirts exhibiting significantly lower densities. We argue that these results considered together demonstrate that cluster are kinematically disturbed by their environment, likely due to galaxy-galaxy interactions (harassment). We then discuss our most powerful method of tracking galaxy evolution across Cl 0024 and MS 0451: identifying and studying transition galaxies-galaxies whose stellar populations or dynamical states indicate a recent or ongoing change in morphology or star formation rate. Such galaxies are often revealed by star formation histories that seem to be at odds with the galaxy morphologies: for example, spiral galaxies with no signs of star formation, or elliptical galaxies that do show signs of star formation. We identify and study one such class of objects, the spirals in Cl 0024. These objects exhibit no emission lines in their spectra, suggesting a lack of star formation, yet are surprisingly detected in the UV, revealing the presence of young stars. By modeling the different temporal sensitivities of UV and spectroscopic data to recent activity, we show that star formation in Cl 0024 passive has decayed on timescales of less than 1 Gyr, consistent with the action of gas starvation. We then build on and link together our previous indications of galaxy evolution at work, aiming to piece together a more comprehensive picture of how cluster galaxies are affected by their environment at intermediate redshift. To accomplish this, we document what we believe to be the first direct evidence for the transformation of into S0s: through an analysis of their stellar populations and recent star formation rates, we link the passive spiral galaxies in both clusters to their eventual end states as newly generated cluster S0 galaxies. Differences between the two clusters in both the timescales and spatial location of this conversion process allow us to evaluate the relative importance of several proposed physical mechanisms that could be responsible for the transformation. Combined with other diagnostics that are sensitive to either ICM-driven galaxy evolution or galaxy-galaxy interactions, we describe a self-consistent picture of galaxy evolution in clusters. We find that spiral galaxies within infalling groups have already begun a slow process of conversion into S0s primarily via gentle galaxy-galaxy interactions that act to quench star formation. The fates of upon reaching the core of the cluster depend heavily on the cluster ICM, with rapid conversion of all remaining into S0s via ram-pressure stripping in clusters where the ICM is dense. In the presence of a less-dense ICM, the conversion continues at a slower pace, with galaxy-galaxy interactions continuing to play a role along with starvation by the ICM. We conclude that the buildup of the local S0 population through the transformation of spiral galaxies is a heterogeneous process that nevertheless proceeds robustly across a variety of different environments from cluster outskirts to cores.

Using the optical data from the Wide component of the CFHT Legacy Survey, and new ultraviolet data from GALEX, we study the colours and specific star formation rates (SSFR) of ~100 galaxy clusters at 0.16<z<0.36, over areas extending out to radii of r~7Mpc. We use a multicolour, statistical background subtraction method to study the galaxy population at this radius; thus our results pertain to those galaxies which constitute an excess over the average field density. We find that the average SSFR, and its distribution, of the star-forming galaxies (with SFR>0.7 M_sun/yr at z~0.2 and SFR>1.2 M_sun/yr at z~0.3) have no measurable dependence on the cluster-centric radius, and are consistent with the field values. However, the fraction of galaxies with SFR above these thresholds, and the fraction of optically blue galaxies, are lower for the overdense galaxy population in the cluster outskirts compared with the average field value, at all stellar masses M*>10^{9.8} M_sun and at all radii out to at least 7Mpc. Most interestingly, the fraction of blue galaxies that are forming stars at a rate below our UV detection limit is much higher in all radial bins around our cluster sample, compared with the general field value. This is most noticeable for massive galaxies M*>10^{10.7} M_sun; while almost all blue field galaxies of this mass have detectable star formation, this is true for less than 20% of the blue cluster galaxies, even at 7Mpc from the cluster centre. Our results support a scenario where galaxies are pre-processed in locally overdense regions, in a way that reduces their SFR below our UV detection limit, but not to zero.

We present the observational properties of the dwarf galaxy population (Mr > M*+1) corresponding to one of the largest samples of spectroscopically confirmed galaxy cluster members reported in the literature. We have observed that red dwarf galaxies (u-r > 2.22) share the same cluster environment as the brightest cluster members (Mr < -21), but are not in dynamical equilibrium. We computed the dwarf-to-giant ratio (DGR) using a spectroscopically selected sample. The DGR was found to vary with clustercentric distance, essentially due to the blue dwarf population (u-r < 2.22). The u-r color of red dwarf galaxies was independent of their environment and similar to the color of red isolated dwarfs. Blue dwarf galaxies located outside r200 show similar u-r colors to those of the field population, while strong reddening was observed toward the cluster center. We also present evidence that the fraction of red to blue dwarf galaxies in clusters is larger in the innermost cluster regions. We conclude that the present red dwarf population observed in the central regions of nearby galaxy clusters could be related to the blue dwarf population observed in clusters at high redshift.

Galaxy clusters' structure, dominated by dark matter, is traced by member galaxies in the optical and hot intra-cluster medium (ICM) in X-rays. We compare the radial distribution of these components and determine the mass-to-light ratio vs. system mass relation. We use 14 clusters from the REXCESS sample which is representative of clusters detected in X-ray surveys. Photometric observations with the Wide Field Imager on the 2.2m MPG/ESO telescope are used to determine the number density profiles of the galaxy distribution out to $r_{200}$. These are compared to electron density profiles of the ICM obtained using XMM-Newton, and dark matter profiles inferred from scaling relations and an NFW model. While red sequence galaxies trace the total matter profile, the blue galaxy distribution is much shallower. We see a deficit of faint galaxies in the central regions of massive and regular clusters, and strong suppression of bright and faint blue galaxies in the centres of cool-core clusters, attributable to ram pressure stripping of gas from blue galaxies in high density regions of ICM and disruption of faint galaxies due to galaxy interactions. We find a mass-to-light ratio vs. mass relation within $r_{200}$ of $\left(3.0\pm0.4\right) \times 10^2\, h\,\mathrm{M}_{\odot}\,\mathrm{L}_{\odot}^{-1}$ at $10^{15}\,\mathrm{M}_{\odot}$ with slope $0.16 \pm 0.14$, consistent with most previous results.

The growth of structure in the Universe is tightly correlated with the cosmological parameters. Galaxy clusters as tracers of the large scale structure are the ideal objects to witness this evolution. The X-ray bright, hot gas in the potential well of a galaxy cluster enables systematic X-ray studies of samples of galaxy clusters to constrain cosmological parameters. HIFLUGCS consists of the 64 X-ray brightest clusters in the Universe, building up a local sample of galaxy clusters. Here we utilize this sample to determine, for the first time, individual hydrostatic mass estimates for all the clusters of the sample and, by making use of the completeness of the sample, we quantify constraints on the two interesting cosmological parameters, OmegaM and sigma8. In paper I we describe the data analysis procedure and compared the individual mass estimates with other references. Now we apply the total hydrostatic and gas mass estimates from the X-ray analysis to a Bayesian cosmological likelihood analysis and leave several parameters free to be constrained. We find OmegaM = 0.30+-0.01 and sigma8 = 0.79+-0.03 (statistical uncertainties, 68% credibility level) using our default analysis strategy combining both, a mass function analysis and the gas mass fraction results. The main sources of biases that we also correct here are (1) the influence of galaxy groups, (2) the hydrostatic mass bias, (3) the extrapolation of the total mass, (4) the theoretical halo mass function and (5) other physical effects. We find that galaxy groups introduce a strong bias, since their number density seems to be over predicted by the halo mass function. On the other hand, baryonic effects as incorporated by recent hydrodynamical simulations do not result in a significant change in the constraints. The total systematic uncertainties (20%) clearly dominate the statistical uncertainties on cosmological parameters.

We analyze a sample of 244 ram-pressure-stripped candidate galaxy members within the virial radius of 62 nearby clusters to determine their velocity anisotropy profile β(r). We use previously determined mass profiles for the 62 clusters to build an ensemble cluster by stacking the 62 cluster samples in projected phase space. We solve the Jeans equation for dynamical equilibrium by two methods, MAMPOSSt and the Jeans inversion technique, and determine β(r) both in parametric form and nonparametrically. The two methods consistently indicate that the orbits of the ram-pressure-stripped candidates are increasingly radial with distance from the cluster center, from almost isotropic (β ≃ 0) at the center, to very radial at the virial radius (β ≃ 0.7). The orbits of cluster galaxies undergoing ram pressure stripping are similar to those of spiral cluster galaxies but more radially elongated at large radii.

Compelling observational evidence indicates that the disc population in galaxy clusters has undergone rapid evolution, transitioning from a dominance of blue spirals to red lenticular galaxies (S0s) over the past sim7 We built a simplified cluster evolutionary model in the standard cosmological framework to constrain the characteristic timescales of this transformation. In our model, all field spirals joining the cluster at various redshifts are subject to ram-pressure stripping (RPS), which removes their gas reservoir leading to the quenching of their star formation on a timescale, t_ s, and to an (initially) unspecified mechanism that transforms them into S0s on a timescale, t_ m. We assume that t_̊m s and t_̊m m are independent and both power-law functions of the galaxy-to-cluster mass ratio, M_⋆/M_̊m cl. We constrained our model using the observed distribution of spirals and S0s in a colour-mass plane from the OmegaWINGS and EDisCS cluster surveys at z and z respectively. Our best-fit model reproduces the data remarkably well, especially at low redshift, and predicts evolutionary trends for the main morphological fractions in agreement with previous studies. We find typical t_̊m s values between 0.1 and 1 compatible with previous estimates, supporting RPS as the most efficient quenching mechanisms in clusters. A surprisingly strong anti-correlation between t_̊m s and M_⋆/M_̊m cl is required in order to suppress the formation of red, low-mass spirals at low redshift, which we interpret as being driven by orbit anisotropy. Conversely, t_̊m m depends very weakly on M_⋆/M_̊m cl and has typical values of a few Gyr. The inferred morphological evolution is compatible with that resulting from the ageing of the stellar populations in galaxies that have been abruptly quenched by ram pressure stripping: we confirm spectrophotometric ageing as a key channel for the spiral-to-S0 transition in galaxy clusters, with secular evolution playing a secondary role.

Aims: Following the study already presented in our previous paper, based on the Nordic Optical Telescope (NOT) sample, which consists of five clusters of galaxies within the redshift range 0.18 $\leq$ z $\leq$ 0.25, imaged in the central 0.5-2 Mpc in very good seeing conditions, we have studied the quantitative morphology of their bright galaxy population Methods: We have analyzed the surface brightness profiles of the galaxy population in those clusters. Previously, we have performed simulations in order to check the reliability of the fits. We have also derived a quantitative morphological classification. Results: The structural parameters derived from these analysis have been analyzed. We have obtained that the structural parameters of E/S0 galaxies are similar to those showed by galaxies in low redshift clusters. However, the disc scales are different. In particular, the scales of the discs of galaxies at medium redshift clusters are statistically different than those located in similar galaxies in the Coma cluster. But, the scales of the discs of galaxies in medium redshift clusters are similar to nearby field galaxies. Conclusions: The results suggest that the evolution of the disc component of galaxies in clusters is faster than in field ones. Mechanisms like galaxy harassment showing timescales of $\sim 1$Gyr could be the responsible of this disc scale evolution. This indicates that spiral galaxies in clusters have suffered a strong evolution in the last 2.5 Gyr or that Coma is in some way anomalous.

We investigate the possibility of transferring the galaxy cluster mass scale calibrations from weak-lensing measurements to X-ray cluster mass measurements using Planck cluster mass measurements. For this purpose, we compare the mass measurements for 47 galaxy clusters that simultaneously enter the X-ray sample of clusters from Vikhlinin et al. (2009a, 2009b) and the sample of galaxy clusters from the second Planck catalogue of Sunyaev-Zeldovich sources. We show that except for a few outliers in the measurements, most of which arise from cluster projection effects in the Planck data, the scatter in the mass ratio turns out to be small, ~15%, while the accuracy of determining the mean mass ratio for this sample is about 2%. This allows the existing cluster mass measurement calibrations in the Planck survey to be transferred to Chandra X-ray mass measurements almost without any loss of accuracy. Using the derived relations and based on new cluster mass scale calibrations from weak-lensing measurements in clusters, we have obtained corrections to the constraints on cosmological parameters from Vikhlinin et al. (2009b). Given these corrections, σ8 increases approximately by 4%, within one standard deviation of the uncertainty in the constraint on this quantity at constant Ωm. We show that, given the systematic uncertainties, all of the currently available galaxy cluster mass function measurements yield approximately identical constraints on the parameters σ8 and Ωm.

Context.The Doppler shift predicted by general relativity for light escaping a gravitational potential has been observed on Earth as well as in the direction of various stars and galaxy clusters at optical wavelengths.Aims.Observing the gravitational redshift in the X-ray band within galaxy clusters could provide information on their properties and, in particular, their gravitational potential. We present a feasibility study of such a measurement, using the capabilities of the next-generation European X-ray observatoryAthena.Methods.We used a simple generalized Navarro–Frenk–White potential model along with aβ-model for the density of baryonic matter, which sets the emission to provide an estimation of the observed redshift in the simplest of cases. We generated mock observations with theAthenaX-ray Integral Field Unit (X-IFU) for a nearby massive cluster, while seeking to recover the gravitational redshift along with other properties of the toy model cluster.Results.We investigated the observability of the gravitational redshift in an idealized test case of a nearby massive cluster with theAthenaX-IFU instrument, as well as its use in probing the properties of the potential well. We were also able to constrain the mass to a ∼20% level of precision and the cosmological redshift to less than ∼1%, within a simplified and idealized observational framework. More refined simulations accounting for further effects such as the internal gas motions and the actual shape of the potential well are required to fully investigate the feasibility of measuring the gravitational redshift for a single target or statistically over a sample of galaxy clusters.

We connect galaxy properties with their orbital classification by analysing a sample of galaxies with stellar mass M⋆ ≥ 108.5h−1M⊙ residing in and around massive and isolated galaxy clusters with mass M200 &amp;gt; 1015h−1M⊙ at redshift z = 0. The galaxy population is generated by applying the semi-analytic model of galaxy formation sag on the cosmological simulation MultiDark Planck 2. We classify galaxies considering their real orbits (3D) and their projected phase-space position using the roger code (2D). We define five categories: cluster galaxies, galaxies that have recently fallen into a cluster, backsplash galaxies, infalling galaxies, and interloper galaxies. For each class, we analyse the 0.1(g − r) colour, the specific star formation rate (sSFR), and the stellar age, as a function of the stellar mass. For the 3D classes, we find that cluster galaxies have the lowest sSFR, and are the reddest and the oldest, as expected from environmental effects. Backsplash galaxies have properties intermediate between the cluster and recent infaller galaxies. For each 2D class, we find an important contamination by other classes. We find it necessary to separate the galaxy populations in red and blue to perform a more realistic analysis of the 2D data. For the red population, the 2D results are in good agreement with the 3D predictions. Nevertheless, when the blue population is considered, the 2D analysis only provides reliable results for recent infallers, infalling galaxies and interloper galaxies.

We used the DEIMOS spectrograph on the Keck II Telescope to obtain spectra of galaxies in the fields of five distant, rich galaxy clusters over the redshift range 0.5 < z < 0.9 in a search for luminous, compact, blue galaxies (LCBGs). Unlike traditional studies of galaxy clusters, we preferentially targeted blue cluster members identified via multi-band photometric pre-selection based on imaging data from the WIYN telescope. Of the 1288 sources that we targeted, we determined secure spectroscopic redshifts for 848 sources, yielding a total success rate of 66%. Our redshift measurements are in good agreement with those previously reported in the literature, except for 11 targets which we believe were previously in error. Within our sample, we confirm the presence of 53 LCBGs in the five galaxy clusters. The clusters all stand out as distinct peaks in the redshift distribution of LCBGs with the average number density of LCBGs ranging from 1.65+-0.25 Mpc^-3 at z=0.55 to 3.13+-0.65 Mpc^-3 at z=0.8. The number density of LCBGs in clustes exceeds the field desnity by a factor of 749+-116 at z=0.55; at z=0.8, the corresponding ratio is E=416+-95. At z=0.55, this enhancement is well above that seen for blue galaxies or the overall cluster population, indicating that LCBGs are preferentially triggered in high-density environments at intermediate redshifts.

As galaxies evolve in dense cluster and protocluster environments, they interact and quench their star formation. This gradually transforms the dominant galaxy population from star-forming galaxies to quiescent red galaxies. This transformation is identifiable by observing the galaxy colors and can also be seen in the morphological transformation of late-type galaxies into early-type galaxies, which creates the morphology-density relation observed when populations in clusters are compared to field galaxies at a given epoch. However, high-z (z $&gt;$ 2) galaxy morphology studies are hindered by the high angular resolution necessary to characterize the morphology. We studied HST WFC3 F160W observations of protoclusters from the MAMMOTH survey (BOSS1244 and BOSS1542) at z ∼ 2.23 with populations of previously identified Hα emitters. By measuring the Sérsic index of 151 Hα emitters, we searched for the early morphological transformation of high-z star-forming galaxies in these well-studied large nonvirialized protoclusters, which we think are the precursors of present-day galaxy clusters. The morphology of the populations of star-forming galaxies in protoclusters does not differ from that of their field counterparts. However, we also identified a population of clumpy potentially merging galaxies, which might increase the population of early-type galaxies within these structures. In BOSS1244, which has two previously identified massive quiescent galaxies including a brightest cluster galaxy (BCG), we additionally found an abundance of early-type galaxies near the BCG and two coeval high-z quasars. Although the morphology of field and protocluster galaxies are very similar, the population of early-type star-forming galaxies surrounding the spectroscopically confirmed quiescent BCG in BOSS1244, which is not observed in BOSS1542, might indicate differences in the evolutionary state of these two coeval protoclusters. It might be a sign of an early forming cluster core in BOSS1244.

Galaxy clusters represent one of the largest-scale structures in the Universe, with their environments of varying density being ideal for inducing an increase in activity of the cluster galaxy members and the pervading Intracluster Medium (ICM) between them.<br> However the precise drivers, thereby the inferred consequences, of differing states of galaxy cluster activity have not been adequately disentangled.<br> If one can procure a sufficient dichotomic sample of cluster galaxies of differing sub-populations from relaxed and unrelaxed galaxy cluster dynamical states, one could analyse how these sub-populations `move' as a function of both radius and dynamical state.<br> Specifically, using velocity dispersion profiles (VDPs) that weight against cluster galaxies across all radii with a Gaussian window function, one can determine how cluster galaxies of properties that pertain to galaxy evolutionary indicators respond to the cluster environment as a function of the clustocentric radius. <br> In addition, analysing the rotational profiles of these sub-populations as a function of the clustocentric radius can help identify where the bulk of the kinetic energy lies.<br> In view of these points, we have pooled data of galaxies from the Sloan Digital Sky Survey (SDSS) two composite galaxy clusters are assembled into unrelaxed and relaxed states, which are compared with one another through splitting their cluster galaxy populations by their evolutionary proxies (i.e. morphology, colour, mass and AGN), thus analysing their resultant VDPs and rotational profiles.<br> It is therefore found that unrelaxed galaxy clusters possess increased interaction between cluster galaxies as the radius increases, driven by blue and red elliptical galaxies, suggesting an induction of activity by pre-processed groups.<br> AGN-hosting cluster galaxy sub-populations within these unrelaxed environs however present increased activity as \(R\rightarrow0\), indicating these are recent infallers, potentially triggered due to interactions with the ICM.<br> Rotational profiles of unrelaxed clusters build upon the VDPs, showing significant bulk rotation of cluster galaxies with prominent core rotation driven by redder sub-populations.

We compile a sample of X-ray-selected galaxy groups and clusters from the XMM-Newton serendipitous source catalogue (2XMMi-DR3) with optical confirmation and redshift measurement from the Sloan Digital Sky Survey (SDSS). The X-ray cluster candidates were selected from the 2XMMi-DR3 catalogue in the footprint of the SDSS-DR7. We developed a finding algorithm to search for overdensities of galaxies at the positions of the X-ray cluster candidates in the photometric redshift space and to measure the redshifts of the clusters from the SDSS data. The detection algorithm provides the photometric redshift of 530 galaxy clusters. Of these, 310 clusters have a spectroscopic redshift for at least one member galaxy. About 75 percent of the optically confirmed cluster sample are newly discovered X-ray clusters. Moreover, 301 systems are known as optically selected clusters in the literature while the remainder are new discoveries in X-ray and optical bands. The optically confirmed cluster sample spans a wide redshift range 0.03-0.70 (median z=0.32). In this paper, we present the catalogue of X-ray-selected galaxy groups and clusters from the 2XMMi/SDSS galaxy cluster survey. The catalogue has two subsamples: (i) a cluster sample comprising 345 objects with their X-ray spectroscopic temperature and flux from the spectral fitting, and (ii) a cluster sample consisting of 185 systems with their X-ray flux from the 2XMMi-DR3 catalogue, because their X-ray data are insufficient for spectral fitting. The updated L_X-T relation of the current sample with X-ray spectroscopic parameters is presented. We see no evidence for evolution in the slope and intrinsic scatter of the L_X-T relation with redshift when excluding the low-luminosity groups.