Showing papers on "Brightest cluster galaxy published in 2009"

Structure and formation of elliptical and spheroidal galaxies

Abstract: New surface photometry of all known elliptical galaxies in the Virgo cluster is combined with published data to derive composite profiles of brightness, ellipticity, position angle, isophote shape, and color over large radius ranges These provide enough leverage to show that S?rsic log I r 1/n functions fit the brightness profiles I(r) of nearly all ellipticals remarkably well over large dynamic ranges Therefore, we can confidently identify departures from these profiles that are diagnostic of galaxy formation Two kinds of departures are seen at small radii All 10 of our ellipticals with total absolute magnitudes MVT ? ?2166 have cuspy cores?missing light?at small radii Cores are well known and naturally scoured by binary black holes (BHs) formed in dissipationless (dry) mergers All 17 ellipticals with ?2154 ? MVT ? ?1553 do not have cores We find a new distinct component in these galaxies: all coreless ellipticals in our sample have extra light at the center above the inward extrapolation of the outer S?rsic profile In large ellipticals, the excess light is spatially resolved and resembles the central components predicted in numerical simulations of mergers of galaxies that contain gas In the simulations, the gas dissipates, falls toward the center, undergoes a starburst, and builds a compact stellar component that, as in our observations, is distinct from the S?rsic-function main body of the elliptical But ellipticals with extra light also contain supermassive BHs We suggest that the starburst has swamped core scouring by binary BHs That is, we interpret extra light components as a signature of formation in dissipative (wet) mergers Besides extra light, we find three new aspects to the (E-E) dichotomy into two types of elliptical galaxies Core galaxies are known to be slowly rotating, to have relatively anisotropic velocity distributions, and to have boxy isophotes We show that they have S?rsic indices n > 4 uncorrelated with MVT They also are ?-element enhanced, implying short star-formation timescales And their stellar populations have a variety of ages but mostly are very old Extra light ellipticals generally rotate rapidly, are more isotropic than core Es, and have disky isophotes We show that they have n 3 ? 1 almost uncorrelated with MVT and younger and less ?-enhanced stellar populations These are new clues to galaxy formation We suggest that extra light ellipticals got their low S?rsic indices by forming in relatively few binary mergers, whereas giant ellipticals have n > 4 because they formed in larger numbers of mergers of more galaxies at once plus later heating during hierarchical clustering We confirm that core Es contain X-ray-emitting gas whereas extra light Es generally do not This leads us to suggest why the E-E dichotomy arose If energy feedback from active galactic nuclei (AGNs) requires a working surface of hot gas, then this is present in core galaxies but absent in extra light galaxies We suggest that AGN energy feedback is a strong function of galaxy mass: it is weak enough in small Es not to prevent merger starbursts but strong enough in giant Es and their progenitors to make dry mergers dry and to protect old stellar populations from late star formation Finally, we verify that there is a strong dichotomy between elliptical and spheroidal galaxies Their properties are consistent with our understanding of their different formation processes: mergers for ellipticals and conversion of late-type galaxies into spheroidals by environmental effects and by energy feedback from supernovae In an appendix, we develop machinery to get realistic error estimates for S?rsic parameters even when they are strongly coupled And we discuss photometric dynamic ranges necessary to get robust results from S?rsic fits

The remnants of galaxy formation from a panoramic survey of the region around M31

Abstract: In hierarchical cosmological models, galaxies grow in mass through the continual accretion of smaller ones. The tidal disruption of these systems is expected to result in loosely bound stars surrounding the galaxy, at distances that reach 10-100 times the radius of the central disk. The number, luminosity and morphology of the relics of this process provide significant clues to galaxy formation history, but obtaining a comprehensive survey of these components is difficult because of their intrinsic faintness and vast extent. Here we report a panoramic survey of the Andromeda galaxy (M31). We detect stars and coherent structures that are almost certainly remnants of dwarf galaxies destroyed by the tidal field of M31. An improved census of their surviving counterparts implies that three-quarters of M31's satellites brighter than M(v) = -6 await discovery. The brightest companion, Triangulum (M33), is surrounded by a stellar structure that provides persuasive evidence for a recent encounter with M31. This panorama of galaxy structure directly confirms the basic tenets of the hierarchical galaxy formation model and reveals the shared history of M31 and M33 in the unceasing build-up of galaxies.

The Relation Between Compact, Quiescent High Redshift Galaxies and Massive Nearby Elliptical Galaxies: Evidence for Hierarchical, Inside-Out Growth

Abstract: Recent studies have shown that massive quiescent galaxies at high redshift are much more compact than present-day galaxies of the same mass. Here we compare the radial stellar density profiles and the number density of a sample of massive galaxies at z ~ 2.3 to nearby massive elliptical galaxies. We confirm that the average stellar densities of the z ~ 2.3 galaxies within the effective radius, rho(

Galaxy Groups in the SDSS DR4. III. The Luminosity and Stellar Mass Functions

Abstract: Using a large galaxy group catalog constructed from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4) with an adaptive halo-based group finder, we investigate the luminosity and stellar mass functions for different populations of galaxies (central versus satellite, red versus blue, and galaxies in groups of different masses) and for groups themselves. The conditional stellarmass function (CSMF), which describes the stellar distribution of galaxies in halos of a given mass for central and satellite galaxies can be well modeled with a log-normal distribution and a modified Schechter form, respectively. On average, there are about three times as many central galaxies as satellites. Among the satellite population, there are in general more red galaxies than blue ones. For the central population, the luminosity function is dominated by red galaxies at the massive end, and by blue galaxies at the low-mass end. At the very low mass end (M(*) less than or similar to 10(9) h(-2) M(circle dot)), however, there is a marked increase in the number of red centrals. We speculate that these galaxies are located close to large halos so that their star formation is truncated by the large-scale environments. The stellarmass function of galaxy groups is well described by a double power law, with a characteristic stellarmass at similar to 4 x 10(10) h(-2) M(circle dot). Finally, we use the observed stellarmass function of central galaxies to constrain the stellar mass-halo mass relation for low-mass halos, and obtain M(*,c) proportional to M(h)(4.9) for M(h) << 10(11) h(-1) M(circle dot).

The accretion of galaxies into groups and clusters

Abstract: We use the galaxy stellar mass and halo merger tree information from the semi-analyticmodel galaxy catalogue of Font et al. (2008) to examine the accretion of galaxies into a large sample of groups and clusters, covering a wide range in halo mass (1012.9 to 1015.3 h−1 M⊙), and selected from each of four redshift epochs (z=0, 0.5, 1.0 and 1.5). We find that clusters at all examined redshifts have accreted a significant fraction of their final galaxy populations through galaxy groups. A 1014.5 h−1 M⊙ mass cluster at z=0 has, on average, accreted_ 40% of its galaxies (Mstellar > 109 h−1 M⊙) from halos with masses greater than 1013 h−1 M⊙. Further, the galaxies which are accreted through groups are more massive, on average, than galaxies accreted through smaller halos or from the field population. We find that at a given epoch, the fraction of galaxies accreted from isolated environments is independent of the final cluster or group mass. In contrast, we find that observing a cluster of the same halo mass at each redshift epoch implies different accretion rates of isolated galaxies, from 5-6 % per Gyr at z=0 to 15% per Gyr at z=1.5. We find that combining the existence of a Butcher Oemler effect at z=0.5 and the observations that galaxies within groups display significant environmental effects with galaxy accretion histories justifies striking conclusions. Namely, that the dominant environmental process must begin to occur in halos of 1012 – 1013 h−1 M⊙, and act over timescales of > 2 Gyrs. This argues in favor of a mechanism like “strangulation”, in which the hot halo of a galaxy is stripped upon infalling into a more massive halo . This simple model predicts that by z=1.5 galaxy groups and clusters will display little to no environmental effects. This conclusion may limit the effectiveness of red sequence cluster finding methods at high redshift.

The Galaxy Content of SDSS Clusters and Groups

Abstract: Imaging data from the Sloan Digital Sky Survey are used to characterize the population of galaxies in groups and clusters detected with the MaxBCG algorithm. We investigate the dependence of brightest cluster galaxy (BCG) luminosity, and the distributions of satellite galaxy luminosity and satellite color, on cluster properties over the redshift range 0.1 {<=} z {<=} 0.3. The size of the data set allows us to make measurements in many bins of cluster richness, radius and redshift. We find that, within r {sub 200} of clusters with mass above 3 x 10{sup 13} h {sup -1} M {sub sun}, the luminosity function (LF) of both red and blue satellites is only weakly dependent on richness. We further find that the shape of the satellite LF does not depend on cluster-centric distance for magnitudes brighter than {sup 0.25} M{sub i} - 5log{sub 10} h =-19. However, the mix of faint red and blue galaxies changes dramatically. The satellite red fraction is dependent on cluster-centric distance, galaxy luminosity, and cluster mass, and also increases by {approx}5% between redshifts 0.28 and 0.2, independent of richness. We find that BCG luminosity is tightly correlated with cluster richness, scaling as L {sub BCG} {approx} Mmore » {sup 0.3} {sub 200}, and has a Gaussian distribution at fixed richness, with {sigma}{sub logL} {approx} 0.17 for massive clusters. The ratios of BCG luminosity to total cluster luminosity and characteristic satellite luminosity scale strongly with cluster richness: in richer systems, BCGs contribute a smaller fraction of the total light, but are brighter compared to typical satellites. This study demonstrates the power of cross-correlation techniques for measuring galaxy populations in purely photometric data.« less

Inspiralling Supermassive Black Holes: A New Signpost for Galaxy Mergers

Abstract: We present a new technique for observationally identifying galaxy mergers spectroscopically rather than through host galaxy imaging Our technique exploits the dynamics of supermassive black holes (SMBHs) powering active galactic nuclei (AGNs) in merger-remnant galaxies Because structure in the universe is built up through galaxy mergers and nearly all galaxies host a central SMBH, some galaxies should possess two SMBHs near their centers as the result of a recent merger These SMBHs spiral to the center of the resultant merger-remnant galaxy, and one or both of the SMBHs may power AGNs Using the DEEP2 Galaxy Redshift Survey, we have examined 1881 red galaxies, of which 91 exhibit [O III] and H? emission lines indicative of Seyfert 2 activity Of these, 32 AGNs have [O III] emission-line redshifts significantly different from the redshifts of the host galaxies' stars, corresponding to velocity offsets of ~50 km s?1 to ~300 km s?1 Two of these AGNs exhibit double-peaked [O III] emission lines, while the remaining 30 AGNs each exhibit a single set of velocity-offset [O III] emission lines After exploring a variety of physical models for these velocity offsets, we argue that the most likely explanation is inspiralling SMBHs in merger-remnant galaxies Based on this interpretation, we find that roughly half of the red galaxies hosting AGNs are also merger remnants, which implies that mergers may trigger AGN activity in red galaxies The AGN velocity offsets we find imply a merger fraction of ~30% and a merger rate of ~3 mergers Gyr?1 for red galaxies at redshifts 034 < z < 082

Environmental effects on satellite galaxies: the link between concentration, size and colour profile

Abstract: Using the Sloan Digital Sky Survey Data Release 4 group catalogue of Yang et al., we investigate sizes, concentrations, colour gradients and surface brightness profiles of central and satellite galaxies. We compare central and satellite galaxies at fixed stellar mass, in order to disentangle environmental from stellar mass dependencies. Early-and late-type galaxies are defined according to concentration. We find that at fixed stellar mass, late-type satellite galaxies have smaller radii and larger concentrations than late-type central galaxies. No such differences are found for early-type galaxies. We have also constructed surface brightness and colour profiles for the central and satellite galaxies in our sample. We find that late-type satellite galaxies have a lower surface brightness and redder colours than late-type central galaxies. We show that all observed differences between satellite and central galaxies can be explained by a simple fading model, in which the star formation in the disc decreases over time-scales of 2-3 Gyr after a galaxy becomes a satellite. Processes that induce strong morphological changes (e. g. harassment) and processes that strip the galaxy of its entire interstellar medium need not to be invoked in order to explain the environmental dependencies we find.

Galaxies in a simulated ΛCDM universe – II. Observable properties and constraints on feedback

Abstract: We compare the properties of galaxies that form in a cosmological simulation without strong feedback to observations of the z = 0 galaxy population. We confirm previous findings that models without strong feedback overproduce the observed galaxy baryonic mass function, especially at the low- and high-mass extremes. Through post-processing we investigate what kinds of feedback would be required to reproduce the statistics of observed galaxy masses and star formation rates. To mimic an extreme form of ‘preventive’ feedback, such as a highly efficient active galactic nucleus ‘radio mode’, we remove all baryonic mass that was originally accreted from shock-heated gas (‘hot-mode’ accretion). This removal does not bring the highmass end of the galaxy mass function into agreement with observations because much of the stellar mass in these systems formed at high redshift from baryons that originally accreted via ‘cold mode’ on to lower mass progenitors. An efficient ‘ejective’ feedback mechanism, such as supernova-driven galactic winds, must reduce the masses of these progenitors before they merge to form today’s massive galaxies. Feedback must also reduce the masses of lower mass z = 0 galaxies, which assemble at lower redshifts and have much lower star formation rates. If we monotonically remap galaxy masses to reproduce the observed mass function, but retain the simulation-predicted star formation rates, we obtain fairly good agreement with the observed sequence of star-forming galaxies. However, we fail to recover the observed population of passive, low star formation rate galaxies, especially at the high-mass end. Suppressing all hotmode accretion improves the agreement for high-mass galaxies, but it worsens the agreement at intermediate masses. Reproducing these z = 0 observations requires a feedback mechanism that dramatically suppresses star formation in a fraction of galaxies, increasing with mass, while leaving star formation rates of other galaxies essentially unchanged.

The STAGES view of red spirals and dusty red galaxies: Mass-dependent quenching of star formation in cluster infall

Abstract: We investigate the properties of optically passive spirals and dusty red galaxies in the A901/2 cluster complex at redshift ∼0.17 using rest-frame near-ultraviolet–optical spectral energy distributions, 24-μm infrared data and Hubble Space Telescope morphologies from the STAGES data set. The cluster sample is based on COMBO-17 redshifts with an rms precision of σcz ≈ 2000 km s −1 . We find that ‘dusty red galaxies’ and ‘optically passive spirals’ in A901/2 are largely the same phenomenon, and that they form stars at a substantial rate, which is only four times lower than that in blue spirals at fixed mass. This star formation is more obscured than in blue galaxies and its optical signatures are weak. They appear predominantly in the stellar mass range of log M∗/M� = [10, 11] where they constitute over half of the star-forming galaxies in the cluster; they are thus a vital ingredient for understanding the overall picture of star formation quenching in clusters. We find that the mean specific star formation rate (SFR) of star-forming galaxies in the cluster is clearly lower than in the field, in contrast to the specific SFR properties of blue galaxies alone, which appear similar in cluster and field. Such a rich red spiral population is best explained if quenching is a slow process and morphological transformation is delayed even more. At log M∗/M� < 10, such galaxies are rare, suggesting that their quenching is fast and accompanied by morphological change. We note that edge-on

EVOLUTION OF THE COLOR-MAGNITUDE RELATION IN GALAXY CLUSTERS AT z ∼ 1 FROM THE ACS INTERMEDIATE REDSHIFT CLUSTER SURVEY

Abstract: We apply detailed observations of the color-magnitude relation (CMR) with the Advanced Camera for Surveys on the Hubble Space Telescope to study galaxy evolution in eight clusters at z 1. The early-type red sequence is well defined and elliptical and lenticular galaxies lie on similar CMRs. We analyze CMR parameters—scatter, slope, and zero point—as a function of redshift, galaxy properties and cluster mass. For bright galaxies (MB – 21 mag). While the bright S0 population consistently shows larger scatter than the ellipticals, the scatter of the latter increases in the peripheral cluster regions. If we interpret these results as due to age differences, bright elliptical galaxies in cluster cores are, on average, older than S0 galaxies and peripheral elliptical galaxies (by about 0.5 Gyr, using a simple, single-burst solar metallicity stellar population model). The CMR zero point, slope, and scatter in the (U – B) z = 0 rest-frame show no significant evolution out to redshift z 1.3 or significant dependence on cluster mass. Two of our clusters display CMR zero points that are redder (by 2σ) than the average (U – B) z = 0 of our sample. We also analyze the fraction of morphological early-type and late-type galaxies on the red sequence. We find that, while in the majority of the clusters most (80% to 90%) of the CMR population is composed of early-type galaxies, in the highest-redshift, low-mass cluster of our sample, the CMR late-type/early-type fractions are similar (50%), with most of the late-type population composed of galaxies classified as S0/a. This trend is not correlated with the cluster's X-ray luminosity, or with its velocity dispersion, and could be a real evolution with redshift.

Galaxy Zoo: Disentangling the Environmental Dependence of Morphology and Colour ⋆

Abstract: We analyze the environmental dependence of galaxy morphology and colour with two-point clustering statistics, using data from the Galaxy Zoo, the largest sample of visually classified morphologies yet compiled, extracted from the Sloan Digital Sky Survey. We present two-point correlation functions of spiral and early-type galaxies, and we quantify the correlation between morphology and environment with marked correlation functions. These yield clear and precise environmental trends across a wide range of scales, analogous to similar measurements with galaxy colours, indicating that the Galaxy Zoo classifications themselves are very precise. We measure morphology marked correlation functions at fixed colour and find that they are relatively weak, with the only residual correlation being that of red galaxies at small scales, indicating a morphology gradient within haloes for red galaxies. At fixed morphology, we find that the environmental dependence of colour remains strong, and these correlations remain for fixed morphology and luminosity. An implication of this is that much of the morphology–density relation is due to the relation between colour and density. Our results also have implications for galaxy evolution: the morphological transformation of galaxies is usually accompanied by a colour transformation, but not necessarily vice versa. A spiral galaxy may move onto the red sequence of the colour-magnitude diagram without quickly becoming an early-type. We analyze the significant population of red spiral galaxies, and present evidence that they tend to be located in moderately dense environments and are often satellite galaxies in the outskirts of haloes. Finally, we combine our results to argue that central and satellite galaxies tend to follow different evolutionary paths.

A high stellar velocity dispersion for a compact massive galaxy at redshift z = 2.186

Abstract: A realization that the oldest and most luminous galaxies in the Universe may be more compact than was thought — cramming a stellar mass similar to that of a present-day elliptical galaxy into much tighter package — is prompting a re-evaluation of some of the assumptions relating to the evolution of galaxies. For instance, it would mean that massive galaxies must have grown in size by a factor of about five during the past ten billion years. If these early galaxies are as small as recent photometric studies suggest, their component stars should be moving with much higher velocities than the stars in present-day galaxies of the same mass, a phenomenon analogous to the rapid rotation of figure skaters drawing their arms inwards. That's something that can be tested, and new observations of a massive compact galaxy at high redshift (z = 2.186) lend support to the high mass/small size combination for the galaxy inferred from photometry, and to the conclusion that massive galaxies of 10 billion years ago were very different from what we see today. The oldest and most luminous galaxies in the early Universe are surprisingly compact, having stellar masses similar to present-day elliptical galaxies but much smaller sizes. This suggests that massive galaxies have grown in size by a factor of about five over the past ten billion years, leading to the expectation that the stars in these galaxies have much higher velocities than those in present-day galaxies of the same mass. Here, the stellar velocity dispersion for a compact massive galaxy at redshift z = 2.186 is indeed found to be very high. Recent studies have found that the oldest and most luminous galaxies in the early Universe are surprisingly compact1,2,3,4,5,6,7, having stellar masses similar to present-day elliptical galaxies but much smaller sizes. This finding has attracted considerable attention8,9,10,11,12,13, as it suggests that massive galaxies have grown in size by a factor of about five over the past ten billion years (10 Gyr). A key test of these results is a determination of the stellar kinematics of one of the compact galaxies: if the sizes of these objects are as extreme as has been claimed, their stars are expected to have much higher velocities than those in present-day galaxies of the same mass. Here we report a measurement of the stellar velocity dispersion of a massive compact galaxy at redshift z = 2.186, corresponding to a look-back time of 10.7 Gyr. The velocity dispersion is very high at km s-1, consistent with the mass and compactness of the galaxy inferred from photometric data. This would indicate significant recent structural and dynamical evolution of massive galaxies over the past 10 Gyr. The uncertainty in the dispersion was determined from simulations that include the effects of noise and template mismatch. However, we cannot exclude the possibility that some subtle systematic effect may have influenced the analysis, given the low signal-to-noise ratio of our spectrum.

AGN heating and ICM cooling in the HIFLUGCS sample of galaxy clusters

Abstract: Active galactic nuclei (AGN) at the center of galaxy clusters with gas cooling times that are much shorter than the Hubble time have emerged as heating agents powerful enough to prevent further cooling of the intracluster medium (ICM). We carried out an intensive study of the AGN heating−ICM cooling network by comparing various cluster parameters to the integrated radio luminosity of the central AGN, LR, defined as the total synchrotron power between 10 MHz and 15 G Hz. This study is based on the HIFLUGCSsample comprising the 64 X-ray brightest galaxy clusters. We adopted the central cooling time, tcool, as the diagnostic to ascertain cooling properties of the HIFLUGCSsample and classify clusters with tcool 7.7 Gyr as non-cool-core (NCC) clusters. We find 48 out of 64 clusters (7 5%) contain cluster center radio sources (CCRS) cospatial with or within 50 h −1 71 kpc of the X-ray peak emission. Furthermore, we find that the p robability of finding a CCRS increases from 45% to 67% to 100% for NCC, WCC, and SCC clusters, respectively. We use a total of∼ 140 independent radio flux-density measurements, with data at more than two frequencies for more than 54% of the sources extending below 500 MHz, enabling the determination of accurate estimates of LR. We find that LR in SCC clusters depends strongly on the cluster scale such that more massive clusters harbor more powerful radio AGN. The same trend is observed between LR and the classical mass deposition rate, ˙ Mclassical in SCC and partly also in WCC clusters, and can be quantified as LR∝ ˙ M 1.69±0.25 classical . We also perform correlations of the luminosity for the brightest cluster galaxy, LBCG, close to the X-ray peak in all 64 clusters with LR and cluster parameters, such as the virial mass, M500, and the bolometric X-ray luminosity, LX. To this end, we use the 2MASS K-band magnitudes and invoke the near-infrared bulge luminosity-black hole mass relation to convert LBCG to supermassive black hole mass, MBH. We find a weak correlation between MBH and LR for SCC clusters, LR∼ M 4.10±0.42 BH , although with a few outliers. We find an excellent correlati on of LBCG with M500 and LX for the entire sample, the SCC clusters showing a tighter trend in both the cases. We discuss the plausible reasons behind these scaling relations in the context of cooling flows and AGN feedback. Our results strongly suggest an AGN-feedback machinery in SCC clusters, which regulates the cooling in the central regions. Since the dispersion in these correlations, such a s that between LR and ˙ Mclassical or LR and MBH, increases in going from SCC to WCC clusters, we conclude there must be secondary processes that work either in conjunction with the AGN heating or independently to counteract the radiative losses in WCC clusters.

Early assembly of the most massive galaxies

Abstract: The current consensus is that galaxies begin as small density fluctuations in the early Universe and grow by in situ star formation and hierarchical merging. Stars begin to form relatively quickly in sub-galactic-sized building blocks called haloes which are subsequently assembled into galaxies. However, exactly when this assembly takes place is a matter of some debate. Here we report that the stellar masses of brightest cluster galaxies, which are the most luminous objects emitting stellar light, some 9 billion years ago are not significantly different from their stellar masses today. Brightest cluster galaxies are almost fully assembled 4-5 billion years after the Big Bang, having grown to more than 90 per cent of their final stellar mass by this time. Our data conflict with the most recent galaxy formation models based on the largest simulations of dark-matter halo development. These models predict protracted formation of brightest cluster galaxies over a Hubble time, with only 22 per cent of the stellar mass assembled at the epoch probed by our sample. Our findings suggest a new picture in which brightest cluster galaxies experience an early period of rapid growth rather than prolonged hierarchical assembly.

Multi-wavelength study of XMMU J2235.3-2557: the most massive galaxy cluster at z > 1

Abstract: Context. The galaxy cluster XMMU J2235.3−2557 (hereafter XMM2235), spectroscopically confirmed at z = 1.39, is one of the most distant X-ray selected galaxy clusters. It has been at the center of a multi-wavelength observing campaign with ground and space facilities. Aims. We characterize the galaxy populations of passive members, the thermodynamical properties and metal abundance of the hot gas, and the total mass of the system using imaging data with HST/ACS (i775 and z850 bands) and VLT/ISAAC (J and KS bands), extensive spectroscopic data obtained with VLT/FORS2, and deep (196 ks) Chandra observations. Methods. Chandra data allow temperature and metallicity to be measured with good accuracy and the X-ray surface brightness profile to be traced out to 1 � (or 500 kpc), thus allowing the mass to be reliably estimated. Out of a total sample of 34 spectroscopically confirmed cluster members, we selected 16 passive galaxies (without detectable [OII]) within the central 2 � (or 1 Mpc) with ACS coverage, and inferred star formation histories for subsamples of galaxies inside and outside the core by modeling their spectrophotometric data with spectral synthesis models. Results. Chandra data show a regular elongated morphology, closely resembling the distribution of core galaxies, with a significant cool core. We measure a global X-ray temperature of kT = 8.6 +1.3 −1.2 keV (68% confidence), which we find to be robust against several systematics involved in the X-ray spectral analysis. By detecting the rest frame 6.7 keV Iron K line in the Chandra spectrum, we measure a metallicity Z = 0.26 +0.20 −0.16 Z� . In the likely hypothesis of hydrostatic equilibrium, we obtain a total mass of Mtot( 1, with a baryonic content, both its galaxy population and intracluster gas, in a significantly advanced evolutionary stage at 1/ 3o f the current age of the Universe.

The environments of starburst and post-starburst galaxies at z=0.4-0.8

Abstract: Post-starburst (E+A or k+a) spectra, characterized by their exceptionally strong Balmer lines in absorption and the lack of emission lines, belong to galaxies in which the star formation (SF) activity ended abruptly sometime during the past Gyr. We perform a spectral analysis of galaxies in clusters, groups, poor groups, and the field at z = 0.4-0.8 based on the ESO Distant Cluster Survey. We find that the incidence of k+a galaxies at these redshifts depends strongly on environment. K+a's reside preferentially in clusters and, unexpectedly, in a subset of the σ = 200-400 km s^(–1) groups, those that have a low fraction of O II emitters. In these environments, 20%-30% of the star-forming galaxies have had their SF activity recently truncated. In contrast, there are proportionally fewer k+a galaxies in the field, the poor groups, and groups with a high O II fraction. An important result is that the incidence of k+a galaxies correlates with the cluster velocity dispersion: more massive clusters have higher proportions of k+a's. Spectra of dusty starburst candidates, with strong Balmer absorption and emission lines, present a very different environmental dependence from k+a's. They are numerous in all environments at z = 0.4-0.8, but they are especially numerous in all types of groups, favoring the hypothesis of triggering by a merger. We present the morphological type, stellar mass, luminosity, mass-to-light ratio, local galaxy density, and clustercentric distance distributions of galaxies of different spectral types. These properties are consistent with previous suggestions that cluster k+a galaxies are observed in a transition phase, at the moment they are rather massive S0 and Sa galaxies, evolving from star-forming, recently infallen later types to passively evolving cluster early-type galaxies. The correlation between k+a fraction and cluster velocity dispersion supports the hypothesis that k+a galaxies in clusters originate from processes related to the intracluster medium, while several possibilities are discussed for the origin of the puzzling k+a frequency in low-O II groups.

Suzaku Observations of Abell 1795: Cluster Emission to R_200

Abstract: We report Suzaku observations of the galaxy cluster Abell 1795 that extend to r_200 ~ 2 Mpc, the radius within which the mean cluster mass density is 200 times the cosmic critical density. These observations are the first to probe the state of the intracluster medium in this object at r > 1.3 Mpc. We sample two disjoint sectors in the cluster outskirts (1.3 0.4 Mpc and find that it falls relatively rapidly (T ~ r^-0.9), reaching a value about one third of its peak at the largest radius we can measure it. Assuming the intracluster medium is in hydrostatic equilibrium and is polytropic, we find a polytropic index of 1.3 +0.3-0.2 and we estimate a mass of 4.1 +0.5-0.3 x 10^14 M_solar within 1.3 Mpc, somewhat (2.7-sigma) lower than that reported by previous observers. However, our observations provide evidence for departure from hydrostatic equilibrium at radii as small as r ~ 1.3 Mpc ~ r_500 in this apparently regular and symmetrical cluster.

The assembly of galaxy clusters

Abstract: We study the formation of fifty-three galaxy cluster-size dark matter halos (M = 10{sup 14.0-14.76} M{sub {circle_dot}}) formed within a pair of cosmological {Lambda}CDM N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host {approx} 0.1L{sub *} galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters experience no 'pre-processing' in the group environment prior to their accretion into the cluster. On average, {approx} 70% of cluster galaxies fall into the cluster potential directly from the field, with no luminous companions in their host halos at the time of accretion; and less than {approx} 12% are accreted as members of groups with five or more galaxies. Moreover, we find that cluster galaxies are significantly less likely to have experienced a merger in the recent past ({approx}< 6 Gyr) than a field halo of the same mass. These results suggest that local, cluster processes like ram-pressure stripping, galaxy harassment, or strangulation play the dominant role in explaining the difference between cluster and field populations at a fixed stellar mass; and that pre-evolution or past merging in the group environment is of secondary importance for setting cluster galaxy properties for mostmore » clusters. The accretion times for z = 0 cluster members are quite extended, with {approx} 20% incorporated into the cluster halo more than 7 Gyr ago and {approx} 20% within the last 2 Gyr. By comparing the observed morphological fractions in cluster and field populations, we estimate an approximate time-scale for late-type to early-type transformation within the cluster environment to be {approx} 6 Gyr.« less

LoCuSS: the connection between brightest cluster galaxy activity, gas cooling and dynamical disturbance of X‐ray cluster cores

Abstract: We study the distribution of projected offsets between the cluster X-ray centroid and the brightest cluster galaxy (BCG) for 65 X-ray-selected clusters from the Local Cluster Substructure Survey, with a median redshift of z = 0.23. We find a clear correlation between X-ray/BCG projected offset and the logarithmic slope of the cluster gas density profile at 0.04r 500 (α), implying that more dynamically disturbed clusters have weaker cool cores. Furthermore, there is a close correspondence between the activity of the BCG, in terms of detected Hα and radio emission, and the X-ray/BCG offset, with the line-emitting galaxies all residing in clusters with X-ray/BCG offsets of ≤15 kpc. Of the BCGs with α 0.02r 500 , indicating that the total mass may be systematically underestimated in clusters with larger X-ray/BCG offsets. Our results imply a link between cool core strength and cluster dynamical state consistent with the view that cluster mergers can significantly perturb cool cores, and set new constraints on models of the evolution of the intracluster medium.

Radial distribution of stars, gas and dust in sings galaxies. I. Surface photometry and morphology

Abstract: We present ultraviolet through far-infrared (FIR) surface brightness profiles for the 75 galaxies in the Spitzer Infrared Nearby Galaxies Survey (SINGS). The imagery used to measure the profiles includes Galaxy Evolution Explorer UV data, optical images from Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory, and Sloan Digital Sky Survey, near-IR data from Two Micron All Sky Survey, and mid- and FIR images from Spitzer. Along with the radial profiles, we also provide multi-wavelength asymptotic magnitudes and several nonparametric indicators of galaxy morphology: the concentration index (C42), the asymmetry (A), the Gini coefficient (G), and the normalized second-order moment of the brightest 20% of the galaxy’s flux (M20). In this paper, the first of a series, we describe the technical aspects regarding the surface photometry, and present a basic analysis of the global and structural properties of the SINGS galaxies at different wavelengths. The homogeneity in the acquisition, reduction, and analysis of the results presented here makes these data ideal for multiple unanticipated studies on the radial distribution of the properties of stars, dust, and gas in galaxies. Our radial profiles show a wide range of morphologies and multiple components (bulges, exponential disks, inner and outer disk truncations, etc.) that vary not only from galaxy to galaxy but also with wavelength for a given object. In the optical and near-IR, the SINGS galaxies occupy the same regions in the C42–A-G-M20 parameter space as other normal galaxies in previous studies. However, they appear much less centrally concentrated, more asymmetric, and with larger values of G when viewed in the UV (due to star-forming clumps scattered across the disk) and in the mid-IR (due to the emission of polycyclic aromatic hydrocarbons at 8.0 μm and very hot dust at 24 μm). In an accompanying paper by Mu˜noz-Mateos et al., we focus on the radial distribution of dust properties in the SINGS galaxies, providing a detailed analysis of the radial variation of the attenuation, the dust column density, the dust-to-gas ratio, the abundance of PAHs, and the intensity of the heating starlight.

The zCOSMOS redshift survey: the role of environment and stellar mass in shaping the rise of the morphology-density relation from z ~ 1

Abstract: For more than two decades we have known that galaxy morphological segregation is present in the Local Universe. It is important to see how this relation evolves with cosmic time. To investigate how galaxy assembly took place with cosmic time, we explore the evolution of the morphology-density relation up to redshift z~1 using about 10000 galaxies drawn from the zCOSMOS Galaxy Redshift Survey. Taking advantage of accurate HST/ACS morphologies from the COSMOS survey, of the well-characterised zCOSMOS 3D environment, and of a large sample of galaxies with spectroscopic redshift, we want to study here the evolution of the morphology-density relation up to z~1 and its dependence on galaxy luminosity and stellar mass. The multi-wavelength coverage of the field also allows a first study of the galaxy morphological segregation dependence on colour. We further attempt to disentangle between processes that occurred early in the history of the Universe or late in the life of galaxies. The zCOSMOS field benefits of high-resolution imaging in the F814W filter from the Advanced Camera for Survey (ACS). We use standard morphology classifiers, optimised for being robust against band-shifting and surface brightness dimming, and a new, objective, and automated method to convert morphological parameters into early, spiral, and irregular types. We use about 10000 galaxies down to I_AB=22.5 with a spectroscopic sampling rate of 33% to characterise the environment of galaxies up to z~1 from the 100 kpc scales of galaxy groups up to the 100 Mpc scales of the cosmic web. ABRIDGED

The distribution of dark matter over three decades in radius in the lensing cluster abell 611

Abstract: We present a detailed analysis of the baryonic and dark matter distribution in the lensing cluster Abell 611 (z = 0.288), with the goal of determining the dark matter profile over an unprecedented range of cluster-centric distance. By combining three complementary probes of the mass distribution, weak lensing from multi-color Subaru imaging, strong lensing constraints based on the identification of multiply imaged sources in Hubble Space Telescope images, and resolved stellar velocity dispersion measures for the brightest cluster galaxy secured using the Keck telescope, we extend the methodology for separating the dark and baryonic mass components introduced by Sand et al. Our resulting dark matter profile samples the cluster from ~3 kpc to 3.25 Mpc, thereby providing an excellent basis for comparisons with recent numerical models. We demonstrate that only by combining our three observational techniques can degeneracies in constraining the form of the dark matter profile be broken on scales crucial for detailed comparisons with numerical simulations. Our analysis reveals that a simple Navarro-Frenk-White (NFW) profile is an unacceptable fit to our data. We confirm earlier claims based on less extensive analyses of other clusters that the inner profile of the dark matter profile deviates significantly from the NFW form and find a inner logarithmic slope β flatter than 0.3 (68%; where ρ_(DM) ∝ r^(–β) at small radii). In order to reconcile our data with cluster formation in a ΛCDM cosmology, we speculate that it may be necessary to revise our understanding of the nature of baryon-dark matter interactions in cluster cores. Comprehensive weak and strong lensing data, when coupled with kinematic information on the brightest cluster galaxy, can readily be applied to a larger sample of clusters to test the universality of these results.

HUBBLE SPACE TELESCOPE WEAK-LENSING STUDY OF THE GALAXY CLUSTER XMMU J2235.3 – 2557 AT z ∼ 1.4: A SURPRISINGLY MASSIVE GALAXY CLUSTER WHEN THE UNIVERSE IS ONE-THIRD OF ITS CURRENT AGE*

Abstract: We present a weak-lensing analysis of the z approx = 1.4 galaxy cluster XMMU J2235.3 - 2557, based on deep Advanced Camera for Surveys images. Despite the observational challenge set by the high redshift of the lens, we detect a substantial lensing signal at the approx>8sigma level. This clear detection is enabled in part by the high mass of the cluster, which is verified by our both parametric and non-parametric estimation of the cluster mass. Assuming that the cluster follows a Navarro-Frenk-White mass profile, we estimate that the projected mass of the cluster within r = 1 Mpc is (8.5 +- 1.7) x 10{sup 14} M {sub sun}, where the error bar includes the statistical uncertainty of the shear profile, the effect of possible interloping background structures, the scatter in concentration parameter, and the error in our estimation of the mean redshift of the background galaxies. The high X-ray temperature 8.6{sup +1.3} {sub -1.2} keV of the cluster recently measured with Chandra is consistent with this high lensing mass. When we adopt the 1sigma lower limit as a mass threshold and use the cosmological parameters favored by the Wilkinson Microwave Anisotropy Probe 5-year (WMAP5) result, the expected number of similarlymore » massive clusters at z approx> 1.4 in the 11 square degree survey is N approx 5 x 10{sup -3}. Therefore, the discovery of the cluster within the survey volume is a rare event with a probability approx<1% and may open new scenarios in our current understanding of cluster formation within the standard cosmological model.« less

Interactions of galaxies in the galaxy cluster environment

Abstract: We study the dependence of galaxy properties on the clustercentric radius and the environment attributed to the nearest neighbor galaxy using the Sloan Digital Sky Survey galaxies associated with the Abell galaxy clusters. We find that there exists a characteristic scale where the properties of galaxies suddenly start to depend on the clustercentric radius at fixed neighbor environment. The characteristic scale is 1-3 times the cluster virial radius depending on galaxy luminosity. Existence of the characteristic scale means that the local galaxy number density is not directly responsible for the morphology-density relation in clusters because the local density varies smoothly with the clustercentric radius and has no discontinuity in general. What is really working in clusters is the morphology-clustercentric radius-neighbor environment relation, where the neighbor environment means both neighbor morphology and the local mass density attributed to the neighbor. The morphology-density relation appears working only because of the statistical correlation between the nearest neighbor distance and the local galaxy number density. We find strong evidence that the hydrodynamic interactions with nearby early-type galaxies is the main drive to quenching star formation activity of late-type galaxies in clusters. The hot cluster gas seems to play at most a minor role down to one tenth of the cluster virial radius. We also find that the viable mechanisms which can account for the clustercentric radius dependence of the structural and internal kinematics parameters are harassment and interaction of galaxies with the cluster potential. The morphology transformation of the late-type galaxies in clusters seems to have taken place through both galaxy-galaxy hydrodynamic interactions and galaxy-cluster/galaxy-galaxy gravitational interactions.

HUBBLE SPACE TELESCOPE OBSERVATIONS OF A SPECTACULAR NEW STRONG-LENSING GALAXY CLUSTER: MACS J1149.5+2223 AT z = 0.544

Abstract: We present Advanced Camera for Surveys observations of MACS?J1149.5+2223, an X-ray luminous galaxy cluster at z = 0.544 discovered by the Massive Cluster Survey. The data reveal at least seven multiply imaged galaxies, three of which we have confirmed spectroscopically. One of these is a spectacular face-on spiral galaxy at z = 1.491, the four images of which are gravitationally magnified by 8 ? 23. We identify this as an L (MB ?20.7), disk-dominated (B/T 0.5) galaxy, forming stars at ~6 M ? yr?1. We use a robust sample of multiply imaged galaxies to constrain a parameterized model of the cluster mass distribution. In addition to the main cluster dark matter halo and the bright cluster galaxies, our best model includes three galaxy-group-sized halos. The relative probability of this model is P(N halo = 4)/P(N halo < 4) ? 1012 where N halo is the number of cluster/group-scale halos. In terms of sheer number of merging cluster/group-scale components, this is the most complex strong-lensing cluster core studied to date. The total cluster mass and fraction of that mass associated with substructures within R ? 500 kpc, are measured to be M tot = (6.7 ? 0.4) ? 1014 M ? and f sub = 0.25 ? 0.12, respectively. Our model also rules out recent claims of a flat density profile at 7? confidence, thus highlighting the critical importance of spectroscopic redshifts of multiply imaged galaxies when modeling strong-lensing clusters. Overall our results attest to the efficiency of X-ray selection in finding the most powerful cluster lenses, including complicated merging systems.

The intrinsic properties of sdss galaxies

Abstract: The observed properties of galaxies vary with inclination; for most applications we would rather have properties that are independent of inclination, intrinsic properties. One way to determine inclination corrections is to consider a large sample of galaxies, study how the observed properties of these galaxies depend on inclination and then remove this dependence to recover the intrinsic properties. We perform such an analysis for galaxies selected from the Sloan Digital Sky Survey which have been matched to galaxies from the Two-Micron All Sky Survey. We determine inclination corrections for these galaxies as a function of galaxy luminosity and Sersic index. In the g-band these corrections reach as as high as 1.2 mag and have a median value of 0.3 mag for all galaxies in our sample. We find that the corrections show little dependence on galaxy luminosity, except in the u band, but are strongly dependent on galaxy Sersic index. We find that the ratio of red-to-blue galaxies changes from 1:1 to 1:2 when going from observed to intrinsic colors for galaxies in the range 22.75 < MK < 17.75. We also discuss how survey completeness and photometric redshifts should be determined when taking into account that observed and intrinsic properties differ. Finally, we examine whether previous determinations of stellar mass give an intrinsic quantity or one that depends on galaxy inclination. Subject headings: galaxies: clusters: general—galaxies: statistics—methods:statistical:surveys

The Distribution of Dark Matter Over 3 Decades in Radius in the Lensing Cluster Abell 611

Abstract: We present a detailed analysis of the baryonic and dark matter distribution in the lensing cluster Abell 611 (z=0.288), with the goal of determining the dark matter profile over an unprecedented range of cluster-centric distance. By combining three complementary probes of the mass distribution, weak lensing from deep multi-color imaging, strong lensing constraints based on the identification of multiply-imaged sources, and resolved stellar velocity dispersion measures for the brightest cluster galaxy (BCG), we extend the methodology for separating the dark and baryonic mass components introduced by Sand et al. (2008). Our resulting dark matter profile samples the cluster from ~3 kpc to 3.25 Mpc, thereby providing an excellent basis for comparisons with recent numerical models. We demonstrate that only by combining our three observational techniques can degeneracies in constraining the form of the dark matter profile be broken on scales crucial for detailed comparisons with numerical simulations. Our analysis reveals that a simple Navarro, Frenk, and White (NFW) profile is an unacceptable fit to our data. We confirm earlier claims that the inner profile of the dark matter profile deviates significantly from the NFW form and find a inner logarithmic slope \beta flatter than 0.3 (68%; where rho_DM ~ r^{-\beta} at small radii). In order to reconcile our data with cluster formation in a LambdaCDM cosmology, we speculate that it may be necessary to revise our understanding of the nature of baryon--dark matter interactions in cluster cores. Comprehensive weak and strong lensing data, when coupled with kinematic information on the brightest cluster galaxy, can readily be applied to a larger sample of clusters to test the universality of these results.

Locuss: the mid-infrared butcher-oemler effect

Abstract: We study the mid-infrared (MIR) properties of galaxies in 30 massive galaxy clusters at 0.02 ≤ z ≤ 0.40, using panoramic Spitzer/MIPS 24 μm and near-infrared data, including 27 new observations from the LoCuSS and ACCESS surveys. This is the largest sample of clusters to date with such high-quality and uniform MIR data covering not only the cluster cores, but extending into the infall regions. We use these data to revisit the so-called Butcher-Oemler (BO) effect, measuring the fraction of massive infrared luminous galaxies (K 5 × 10^(10) L_☉) within r_(200), finding a steady increase in the fraction with redshift from ~3% at z = 0.02 to ~10% by z = 0.30, and an rms cluster-to-cluster scatter about this trend of 0.03. The best-fit redshift evolution model of the form f_(SF) ∝ (1 + z)^n has n = 5.7^(+2.1)_(–1.8), which is stronger redshift evolution than that of L*_(IR) in both clusters and the field. We find that, statistically, this excess is associated with galaxies found at large cluster-centric radii, specifically r_(500) < r < r_(200), implying that the MIR BO effect can be explained by a combination of both the global decline in star formation in the universe since z ~ 1 and enhanced star formation in the infall regions of clusters at intermediate redshifts. This picture is supported by a simple infall model based on the Millennium Simulation semianalytic galaxy catalogs, whereby star formation in infalling galaxies is instantaneously quenched upon their first passage through the cluster, in that the observed radial trends of f_(SF) trace those inferred from the simulations. The observed f SF values, however, lie systematically above the predictions, suggesting an overall excess of star formation, either due to triggering by environmental processes, or a gradual quenching. We also find that f SF does not depend on simple indicators of the dynamical state of clusters, including the offset between the brightest cluster galaxy and the peak of the X-ray emission. This is consistent with the picture described above in that most new star formation in clusters occurs in the infall regions, and is thus not sensitive to the details of cluster-cluster mergers in the core regions.

GMASS ultradeep spectroscopy of galaxies at z ~ 2 - V. Witnessing the assembly at z = 1.6 of a galaxy cluster

Abstract: Context. Clusters of galaxies represent important laboratories for studying galaxy evolution and formation. Well established and relaxed clusters are known below $z 2$, but the in-between redshift range, during which clusters are expected to undergo significant changes, is almost unexplored. Aims. By studying a galaxy overdensity in redshift and angular distribution at $z = 1.6$, uncovered in the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS), we provide insight into the evolution of cluster galaxies at high redshift. Methods. We present a study of the significance of the galaxy overdensity at $z = 1.6$, Cl 0332-2742, its velocity dispersion, and X-ray emission. We identify the colour bimodality of the cluster members and compare the properties of members of Cl 0332-2742 with galaxies outside the overdensity. Results. From the redshifts of the 42 overdensity members, we measure a velocity dispersion of 500 km s -1 . We conservatively estimate the overdensity in redshift space for the spike at $z=1.6$ in the GMASS field to be $8.3\,\pm\,1.5$. A map of the surface density of galaxies at $z=1.6$ in the GMASS field shows that its structure is irregular with several filaments and local overdensities. The differences in the physical properties of Cl 0332-2742 member and field galaxies agree with the latest hierarchical galaxy formation models: for overdensity members, the star formation rate (${\it SFR}$), and specific ${\it SFR}$, is approximately 50% lower than for the field galaxies; overdensity galaxies are twice the age, on average, of field galaxies; and there is a higher proportion of both massive ($M > 10^{10.7}M_\odot$), and early-type galaxies, inside Cl 0332-2742 than in the field. Among the 42 members, seven have spectra consistent with being passively evolving, massive galaxies. These are all located within an area where the surface density of $z=1.6$ galaxies is highest. In a $z-J$ colour–magnitude diagram, the photometric data of these early-type galaxies are in close agreement with a theoretical red sequence of a galaxy cluster at redshift $z = 1.6$, which formed most of its stars in a short burst of star formation at $z \sim 3$. Conclusions. We conclude that the redshift spike at $z=1.6$ in the GMASS field represents a sheet-like structure in the cosmic web, and that the area with the highest surface density within this structure, containing already seven passively evolving galaxies, will evolve into a cluster of galaxies at a later time.