Showing papers on "Brightest cluster galaxy published in 2011"

Galaxy Clustering in the Completed SDSS Redshift Survey: The Dependence on Color and Luminosity

Abstract: We measure the luminosity and color dependence of galaxy clustering in the largest-ever galaxy redshift survey, the main galaxy sample of the Sloan Digital Sky Survey (SDSS) Seventh Data Release (DR7). We focus on the projected correlation function wp(rp) of volume-limited samples, extracted from the parent sample of ∼ 700,000 galaxies over 8000 deg 2 , extending up to redshift of 0.25. We interpret our measurements using halo occupation distribution (HOD) modeling assuming aCDM cosmol- ogy (inflationary cold dark matter with a cosmological constant). The amplitude of wp(rp) grows slowly with luminosity for L L) × (�8/0.8) = 1.06 + 0.21(L/L∗) 1.12 , where L is the sample luminosity threshold. At fixed luminosity, redder galaxies exhibit a higher amplitude and steeper correlation function, a steady trend that runs through the "blue cloud" and "green valley" and continues across the "red sequence." The cross-correlation of red and blue galaxies is close to the geometric mean of their auto- correlations, dropping slightly below at rp 4L∗, but the lowest luminosity red galaxies (0.04−0.25L∗) show very strong clustering on small scales (rp < 2h −1 Mpc). Most of the observed trends can be naturally understood within theCDM+HOD framework. The growth of wp(rp) for higher luminosity galaxies reflects an overall shift in the mass scale of their host dark matter halos, in particular an increase in the minimum host halo mass Mmin. The mass at which a halo has, on average, one satellite galaxy brighter than L is M1 ≈ 17Mmin(L) over most of the luminosity range, with a smaller ratio above L∗. The growth and steepening of wp(rp) for redder galaxies reflects the increasing fraction of galaxies that are satellite systems in high mass halos instead of central systems in low mass halos, a trend that is especially marked at low luminosities. Our exten- sive measurements, provided in tabular form, will allow detailed tests of theoretical models of galaxy formation, a firm grounding of semi-empirical models of the galaxy population, and new constraints on cosmological parameters from combining real-space galaxy clustering with mass-sensitive statistics such as redshift-space distortions, cluster mass-to-light ratios, and galaxy-galaxy lensing. Subject headings: cosmology: observations — cosmology: theory — galaxies: distances and redshifts — galaxies: halos — galaxies: statistics — large-scale structure of universe

The environmental history of group and cluster galaxies in a LambdaCDM Universe

Abstract: We use publicly available galaxy merger trees, obtained applying semi-analytic techniques to a large high resolution cosmological simulation, to study the environmental history of group and cluster galaxies. Our results highlight the existence of an intrinsic history bias which makes the nature versus nurture (as well as the mass versus environment) debate inherently ill posed. In particular we show that: (i) surviving massive satellites were accreted later than their less massive counterparts, from more massive haloes; (ii) the mixing of galaxy populations is incomplete during halo assembly, which creates a correlation between the time a galaxy becomes satellite and its present distance from the parent halo centre. The weakest trends are found for the most massive satellites, as a result of efficient dynamical friction and late formation times of massive haloes. A large fraction of the most massive group/cluster members are accreted onto the main progenitor of the final halo as central galaxies, while about half of the galaxies with low and intermediate stellar mass are accreted as satellites. Large fractions of group and cluster galaxies (in particular those of low stellar mass) have therefore been `pre-processed' as satellites of groups with mass ~10^13 Msun. To quantify the relevance of hierarchical structure growth on the observed environmental trends, we have considered observational estimates of the passive galaxy fractions, and their variation as a function of halo mass and cluster-centric distance. Comparisons with our theoretical predictions require relatively long times (~5-7 Gyr) for the suppression of star formation in group and cluster satellites. [abridged]

A mature cluster with X-ray emission at z = 2.07

Abstract: We report evidence of a fully established galaxy cluster at z = 2.07, consisting of a ∼20σ overdensity of red, compact spheroidal galaxies spatially coinciding with extended X-ray emission detected with XMM-Newton. We use VLT VIMOS and FORS2 spectra and deep Subaru, VLT and Spitzer imaging to estimate the redshift of the structure from a prominent z = 2.07 spectroscopic redshift spike of emission-line galaxies, concordant with the accurate 12-band photometric redshifts of the red galaxies. Using NICMOS and Keck AO observations, we find that the red galaxies have elliptical morphologies and compact cores. While they do not form a tight red sequence, their colours are consistent with that of a 1.3 Gyr population observed at z ∼ 2.1. From an X-ray luminosity of 7.2 × 10 43 erg s −1 and the stellar mass content of the red galaxy population, we estimate a halo mass of 5.3–8 × 10 13 M� , comparable to the nearby Virgo cluster. These properties imply that this structure could be the most distant, mature cluster known to date and that X-ray luminous, elliptical-dominated clusters are already forming at substantially earlier epochs than previously known.

Far-Infrared Line Deficits in Galaxies with Extreme Lfir/MH2 Ratios

Abstract: We report initial results from the far-infrared fine structure line observations of a sample of 44 local starbursts, Seyfert galaxies and infrared luminous galaxies obtained with the PACS spectrometer on board Herschel. We show that the ratio between the far-infrared luminosity and the molecular gas mass, Lfir/MH2, is a much better proxy for the relative brightness of the far-infrared lines than Lfir alone. Galaxies with high Lfir/MH2 ratios tend to have weaker fine structure lines relative to their far-infrared continuum than galaxies with Lfir/MH2 < 80 Lsun/Msun. A deficit of the [C II] 158 micron line relative to Lfir was previously found with the ISO satellite, but now we show for the first time that this is a general aspect of all far-infrared fine structure lines, regardless of their origin in the ionized or neutral phase of the interstellar medium. The Lfir/MH2 value where these line deficits start to manifest is similar to the limit that separates between the two modes of star formation recently found in galaxies on the basis of studies of their gas-star formation relations. Our finding that the properties of the interstellar medium are also significantly different in these regimes provides independent support for the different star forming relations in normal disk galaxies and major merger systems. We use the spectral synthesis code Cloudy to model the emission of the lines. The expected increase of the ionization parameter with Lfir/MH2 can simultaneously explain the line deficits in the [C II], [N II] and [O I] lines.

Are Brightest Halo Galaxies Central Galaxies

Abstract: It is generally assumed that the central galaxy in a dark matter halo, that is the galaxy with the lowest specific potential energy, is also the brightest halo galaxy (BHG), and that it resides at rest at the centre of the dark matter potential well. This central galaxy paradigm (CGP) is an essential assumption made in various fields of astronomical research. In this paper, we test the validity of the CGP using a large galaxy group catalogue constructed from the Sloan Digital Sky Survey. For each group, we compute two statistics, and , which quantify the offsets of the line-of-sight velocities and projected positions of brightest group galaxies relative to the other group members. By comparing the cumulative distributions of and to those obtained from detailed mock group catalogues, we rule out the null hypothesis that the CGP is correct. Rather, the data indicate that in a non-zero fraction f(BNC)(M) of all haloes of mass M the BHG is not the central galaxy, but instead a satellite galaxy. In particular, we find that f(BNC) increases from similar to 0.25 in low-mass haloes (1012 h-1

The small covering factor of cold accretion streams

Abstract: Theoretical models of galaxy formation predict that galaxies acquire most of their baryons via cold mode accretion. Observations of high-redshift galaxies, while showing ubiquitous outflows, have so far not revealed convincing traces of the predicted cold streams, which has been interpreted as a challenge for the current models. Using high-resolution, zoom-in smooth particle hydrodynamics simulations of Lyman break galaxy (LBG) haloes combined with ionizing radiative transfer, we quantify the covering factor of the cold streams at z= 2–4. We focus specifically on Lyman limit systems (LLSs) and damped Lyα absorbers (DLAs), which can be probed by absorption spectroscopy using a background galaxy or quasar sightline, and which are closely related to low-ionization metal absorbers. We show that the covering factor of these systems is relatively small and decreases with time. At z= 2, the covering factor of DLAs within the virial radius of the simulated galaxies is ∼3 per cent (∼1 per cent within twice this projected distance), and arises principally from the galaxy itself. The corresponding values for LLSs are ∼10 and 4 per cent. Because of their small covering factor compared to the order unity covering fraction expected for galactic winds, the cold streams are naturally dominated by outflows in stacked spectra. We conclude that the existing observations are consistent with the predictions of cold mode accretion, and outline promising kinematic and chemical diagnostics to separate out the signatures of galactic accretion and feedback.

Near-IR Atlas of S0-Sa galaxies (NIRS0S)

Abstract: An atlas of Ks-band images of 206 early-type galaxies is presented, including 160 S0-S0/a galaxies, 12 ellipticals, and 33 Sa galaxies. A majority of the Atlas galaxies belong to a magnitude-limited (mB<12.5 mag) sample of 185 NIRS0S (Near-IR S0 galaxy Survey) galaxies. To assure that mis-classified S0s are not omitted, 25 ellipticals from RC3 classified as S0s in the Carnegie Atlas were included in the sample. The images are 2-3 mag deeper than 2MASS images. Both visual and photometric classifications are made. Special attention is paid to the classification of lenses, coded in a systematic manner. A new lens-type, called a 'barlens', is introduced. Also, boxy/peanut/x-shaped structures are identified in many barred galaxies, even-though the galaxies are not seen in edge-on view, indicating that vertical thickening is not enough to explain them. Multiple lenses appear in 25% of the Atlas galaxies, which is a challenge to the hierarchical evolutionary picture of galaxies. Such models need to explain how the lenses were formed and survived in multiple merger events that galaxies may have suffered during their lifetimes. Following the early suggestion by van den Bergh, candidates of S0c galaxies are shown, which galaxies are expected to be former Sc-type spirals stripped out of gas.

Physical Properties of Galaxies from z = 2–4

Abstract: The epoch of galaxy assembly from 2⩽z⩽4 marks a critical stage during the evolution of today's galaxy population. During this period, the star-formation activity in the Universe was at its peak level, and the structural patterns observed among galaxies in the local Universe were not yet in place. A variety of novel techniques have been employed over the past decade to assemble multiwavelength observations of galaxies during this important epoch. In this primarily observational review, I present a census of the methods used to find distant galaxies and the empirical constraints on their multiwavelength luminosities and colors. I then discuss what is known about the stellar content and past histories of star formation in high-redshift galaxies; their interstellar contents including dust, gas, and heavy elements; and their structural and dynamical properties. I conclude by considering some of the most pressing and open questions regarding the physics of high-redshift galaxies, which are to be addressed with ...

An optical catalog of galaxy clusters obtained from an adaptive matched filter finder applied to sloan digital sky survey data release 6

Abstract: We present a new cluster catalog extracted from the Sloan Digital Sky Survey Data Release 6 (SDSS DR6) using an adaptive matched filter (AMF) cluster finder. We identify 69,173 galaxy clusters in the redshift range 0.045 ≤ z < 0.78 in 8420 deg2 of the sky. We provide angular position, redshift, richness, core, and virial radii estimates for these clusters, as well as an error analysis for each of these quantities. We also provide a catalog of more than 205,000 galaxies representing the three brightest galaxies in the r band which are possible brightest cluster galaxy (BCG) candidates. We show basic properties of the BCG candidates and study how their luminosity scales in redshift and cluster richness. We compare our catalog with the maxBCG and GMBCG catalogs, as well as with that of Wen et al. We match between 30% and 50% of clusters between catalogs over all overlapping redshift ranges. We find that the percentage of matches increases with the richness for all catalogs. We cross match the AMF catalog with available X-ray data in the same area of the sky and find 539 matches, 119 of which with temperature measurements. We present scaling relations between optical and X-ray properties and cluster center comparison. We find that both Λ200 and R 200 correlate well with both LX and TX , with no significant difference in trend if we restrict the matches to flux-limited X-ray samples.

A wide Chandra view of the core of the Perseus cluster

Abstract: We present new Chandra images of the X-ray emission from the core of the Perseus cluster of galaxies. The total observation time is now 1.4 Ms. New depressions in X-ray surface brightness are discovered to the north of NGC 1275, which we interpret as old rising bubbles. They imply that bubbles are long-lived and do not readily breakup when rising in the hot cluster atmosphere. The existence of a 300 kpc long NNW‐SSW bubble axis means there cannot be significant transverse large scale flows exceeding 100 km s 1 . Interesting spatial correlations are seen along that axis in early deep radio maps. A semi-circular cold front about 100 kpc west of the nucleus is seen. It separates an inner disturbed region dominated by the activity of the active nucleus of NGC 1275 from the outer region where a subcluster merger dominates.

The hst/acs coma cluster survey. iv. intergalactic globular clusters and the massive globular cluster system at the core of the coma galaxy cluster

Abstract: Intracluster stellar populations are a natural result of tidal interactions in galaxy clusters. Measuring these populations is difficult, but important for understanding the assembly of the most massive galaxies. The Coma cluster of galaxies is one of the nearest truly massive galaxy clusters and is host to a correspondingly large system of globular clusters (GCs). We use imaging from the HST/ACS Coma Cluster Survey to present the first definitive detection of a large population of intracluster GCs (IGCs) that fills the Coma cluster core and is not associated with individual galaxies. The GC surface density profile around the central massive elliptical galaxy, NGC 4874, is dominated at large radii by a population of IGCs that extend to the limit of our data (R <520 kpc). We estimate that there are 47, 000 ± 1600 (random) +4000 -5000 (systematic) IGCs out to this radius, and that they make up ~70% of the central GC system, making this the largest GC system in the nearby universe. Even including the GC systems of other cluster galaxies, the IGCs still make up ~30%-45% of the GCs in the cluster core. Observational limits from previous studies of the intracluster light (ICL) suggest that the IGC population has a high specific frequency. If the IGC population has a specific frequency similar to high-SN dwarf galaxies, then the ICL has a mean surface brightness of μ V ≈ 27 mag arcsec-2 and a total stellar mass of roughly 10^{12} {M}_⊙ within the cluster core. The ICL makes up approximately half of the stellar luminosity and one-third of the stellar mass of the central (NGC 4874+ICL) system. The color distribution of the IGC population is bimodal, with blue, metal-poor GCs outnumbering red, metal-rich GCs by a ratio of 4:1. The inner GCs associated with NGC 4874 also have a bimodal distribution in color, but with a redder metal-poor population. The fraction of red IGCs (20%), and the red color of those GCs, implies that IGCs can originate from the halos of relatively massive, L* galaxies, and not solely from the disruption of dwarf galaxies. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

DISCOVERY AND COSMOLOGICAL IMPLICATIONS OF SPT-CL J2106-5844, THE MOST MASSIVE KNOWN CLUSTER AT z > 1

Abstract: Using the South Pole Telescope (SPT), we have discovered the most massive known galaxy cluster at z>1, SPT-CL J2106-5844. In addition to producing a strong Sunyaev-Zel'dovich (SZ) effect signal, this system is a luminous X-ray source and its numerous constituent galaxies display spatial and color clustering, all indicating the presence of a massive galaxy cluster. Very Large Telescope and Magellan spectroscopy of 18 member galaxies shows that the cluster is at z = 1.132^(+0.002)_(–0.003). Chandra observations obtained through a combined HRC-ACIS GTO program reveal an X-ray spectrum with an Fe K line redshifted by z = 1.18 ± 0.03. These redshifts are consistent with the galaxy colors found in optical, near-infrared, and mid-infrared imaging. SPT-CL J2106-5844 displays extreme X-ray properties for a cluster having a core-excluded temperature of T_X = 11.0^(+2.6)_(–1.9) keV and a luminosity (within r _(500)) of LX (0.5-2.0 keV) = (13.9 ± 1.0) × 10_(44) erg s^(–1). The combined mass estimate from measurements of the SZ effect and X-ray data is M_(200) = (1.27 ± 0.21) × 10^(15) h ^(–1) _(70) M_⊙. The discovery of such a massive gravitationally collapsed system at high redshift provides an interesting laboratory for galaxy formation and evolution, and is a probe of extreme perturbations of the primordial matter density field. We discuss the latter, determining that, under the assumption of ΛCDM cosmology with only Gaussian perturbations, there is only a 7% chance of finding a galaxy cluster similar to SPT-CL J2106-5844 in the 2500 deg^2 SPT survey region and that only one such galaxy cluster is expected in the entire sky.

Demographics of bulge types within 11 Mpc and implications for galaxy evolution

Abstract: We present an inventory of galaxy bulge types (elliptical galaxy, classical bulge, pseudobulge, and bulgeless galaxy) in a volume-limited sample within the local 11 Mpc sphere using Spitzer 3.6 μm and Hubble Space Telescope data. We find that whether counting by number, star formation rate, or stellar mass, the dominant galaxy type in the local universe has pure disk characteristics (either hosting a pseudobulge or being bulgeless). Galaxies that contain either a pseudobulge or no bulge combine to account for over 80% of the number of galaxies above a stellar mass of 109 M ☉. Classical bulges and elliptical galaxies account for ~1/4, and disks for ~3/4 of the stellar mass in the local 11 Mpc. About 2/3 of all star formation in the local volume takes place in galaxies with pseudobulges. Looking at the fraction of galaxies with different bulge types as a function of stellar mass, we find that the frequency of classical bulges strongly increases with stellar mass, and comes to dominate above 1010.5 M ☉. Galaxies with pseudobulges dominate at 109.5-1010.5 M ☉. Yet lower-mass galaxies are most likely to be bulgeless. If pseudobulges are not a product of mergers, then the frequency of pseudobulges in the local universe poses a challenge for galaxy evolution models.

First Results from the 3D-HST Survey: The Striking Diversity of Massive Galaxies at z>1

Abstract: We present first results from the 3D-HST program, a near-IR spectroscopic survey performed with the Wide Field Camera 3 (WFC3) on the HST. We have used 3D-HST spectra to measure redshifts and Hα equivalent widths (EWHα) for a complete, stellar mass-limited sample of 34 galaxies at 1 10^(11) M_☉ in the COSMOS, GOODS, and AEGIS fields. We find that a substantial fraction of massive galaxies at this epoch are forming stars at a high rate: the fraction of galaxies with EW_(Hα) >10 A is 59%, compared to 10% among Sloan Digital Sky Survey galaxies of similar masses at z = 0.1. Galaxies with weak Hα emission show absorption lines typical of 2-4 Gyr old stellar populations. The structural parameters of the galaxies, derived from the associated WFC3 F140W imaging data, correlate with the presence of Hα; quiescent galaxies are compact with high Sersic index and high inferred velocity dispersion, whereas star-forming galaxies are typically large two-armed spiral galaxies, with low Sersic index. Some of these star-forming galaxies might be progenitors of the most massive S0 and Sa galaxies. Our results challenge the idea that galaxies at fixed mass form a homogeneous population with small scatter in their properties. Instead, we find that massive galaxies form a highly diverse population at z > 1, in marked contrast to the local universe.

The effects of baryon physics, black holes and AGN feedback on the mass distribution in clusters of galaxies

Abstract: The spatial distribution of matter in clusters of galaxies is mainly determined by the dominant dark matter component, however, physical processes involving baryonic matter are able to modify it significantly. We analyse a set of 500 pc resolution cosmological simulations of a cluster of galaxies with mass comparable to Virgo, performed with the AMR code RAMSES. We compare the mass density profiles of the dark, stellar and gaseous matter components of the cluster that result from different assumptions for the subgrid baryonic physics and galaxy formation processes. First, the prediction of a gravity only N-body simulation is compared to that of a hydrodynamical simulation with standard galaxy formation recipes, then all results are compared to a hydrodynamical simulation which includes thermal AGN feedback from Super Massive Black Holes (SMBH). We find the usual effects of overcooling and adiabatic contraction in the run with standard galaxy formation physics, but very different results are found when implementing SMBHs and AGN feedback. Star formation is strongly quenched, producing lower stellar densities throughout the cluster, and much less cold gas is available for star formation at low redshifts. At redshift z = 0 we find a flat density core of radius 10 kpc in both of the dark and stellar matter density profiles. We specu- late on the possible formation mechanisms able to produce such cores and we conclude that they can be produced through the coupling of different processes: (I) dynamical friction from the decay of black hole orbits during galaxy mergers; (II) AGN driven gas outflows producing fluctuations of the gravitational potential causing the removal of collisionless matter from the central region of the cluster; (III) adiabatic expansion in response to the slow expulsion of gas from the central region of the cluster during the quiescent mode of AGN activity.

Black hole accretion and host galaxies of obscured quasars in XMM-COSMOS

Abstract: Aims. We explore the connection between black hole growth at the center of obscured quasars selected from the XMM-COSMOS survey and the physical properties of their host galaxies. We study a bolometric regime ( ⟨ L_(bol) ⟩ = 8 × 10^(45) erg s^(-1)) where several theoretical models invoke major galaxy mergers as the main fueling channel for black hole accretion. Methods. To derive robust estimates of the host galaxy properties, we use an SED fitting technique to distinguish the AGN and host galaxy emission. We evaluate the effect on galaxy properties estimates of being unable to remove the nuclear emission from the SED. The superb multi-wavelength coverage of the COSMOS field allows us to obtain reliable estimates of the total stellar masses and star formation rates (SFRs) of the hosts. We supplement this information with a morphological analysis of the ACS/HST images, optical spectroscopy, and an X-ray spectral analysis. Results. We confirm that obscured quasars mainly reside in massive galaxies (M_⋆ > 10^(10)M_⊙) and that the fraction of galaxies hosting such powerful quasars monotonically increases with the stellar mass. We stress the limitation of the use of rest-frame color − magnitude diagrams as a diagnostic tool for studying galaxy evolution and inferring the influence that AGN activity can have on such a process. We instead use the correlation between SFR and stellar mass found for star-forming galaxies to discuss the physical properties of the hosts. We find that at z ~ 1, ≈62% of Type-2 QSOs hosts are actively forming stars and that their rates are comparable to those measured for normal star-forming galaxies. The fraction of star-forming hosts increases with redshift: ≈ 71% at z ~ 2, and 100% at z ~ 3. We also find that the evolution from z ~ 1 to z ~ 3 of the specific SFR of the Type-2 QSO hosts is in excellent agreement with that measured for star-forming galaxies. From the morphological analysis, we conclude that most of the objects are bulge-dominated galaxies, and that only a few of them exhibit signs of recent mergers or disks. Finally, bulge-dominated galaxies tend to host Type-2 QSOs with low Eddington ratios (λ 0.1).

Testing the low-mass end of X-ray scaling relations with a sample of Chandra galaxy groups

Abstract: Context. Well-determined scaling relations between X-ray observables and cluster mass are essential for using large cluster samples to constrain fundamental cosmological parameters. Scaling relations between cluster masses and observables, such as the luminosity-temperature, mass-temperature, luminosity-mass relations, have been investigated extensively, however the question of whether these relations hold true also for poor clusters and groups remains unsettled. Some evidence supports a “break” at the low end of the group/cluster mass range, possibly caused by the stronger influence of non-gravitational physics on low-mass systems.Aims. The main goal of this work is to test local scaling relations for the low-mass range in order to check whether or not there is a systematic difference between clusters and groups, and to thereby extend this method of reliable and convenient cluster mass determination for future large samples down to the group regime.Methods. We compiled a statistically complete sample of 112 X-ray galaxy groups, 26 of which have usable Chandra data. Temperature, metallicity, and surface brightness profiles were created for these 26 groups, and used to determine the main physical quantities and scaling relations. We then compared the group properties to those of the HIFLUGCS clusters, as well as several other group and cluster samples.Results. We present radial profiles for the individual objects and scaling relations of the whole sample (L x − T , M − T , L x − M , M g − M , M − Y x , L x − Y x , f g − T ). Temperature and metallicity profiles behave universally, except for the core regions. The L x − T , M − T , L x − M , M g − M , M − Y x , and L x − Y x relations of the group sample are generally in good agreement with clusters. The L x − T relation steepens for T We have found some evidence for a similarity break between groups and clusters. However this does not have a strong effect on the scaling relations.

Extreme AGN feedback in the Massive Cluster Survey (MACS): a detailed study of X-ray cavities at z > 0.3

Abstract: We present the first statistical study of X-ray cavities in distant clusters of galaxies (z > 0.3). With the aim of providing further insight into how AGN feedback operates at higher redshift, we have analysed the Chandra X-ray observations of the Massive Cluster Survey (MACS) and searched for surface-brightness depressions associated with the Brightest Cluster Galaxy (BCG). The MACS sample consists of the most X-ray luminous clusters within 0.3 10^44 erg/s) starts to operate as early as 7 - 8 Gyrs after the Big Bang and shows no sign of evolution since then. In other words, AGNs lying at the centre of clusters are able to operate at early times with extreme mechanical powers, and have been operating in such a way for at least the past 5 Gyrs.

A deep probe of the galaxy stellar mass functions at z ∼ 1―3 with the GOODS NICMOS Survey

Abstract: We use a sample of 8298 galaxies observed as part of the Hubble Space Telescope (HST) H 160 -band GOODS NICMOS Survey (GNS) to construct the galaxy stellar mass function both as a function of redshift and as stellar mass up to z = 3.5. Our mass functions are constructed within the redshift range z = 1-3.5 and consist of galaxies with stellar masses of M * = 10 12 M ⊙ down to nearly dwarf galaxy masses of M * = 10 8.5 M ⊙ in the lowest redshift bin. We discover that a significant fraction of all massive M * > 10 11 M ⊙ galaxies are in place up to the highest redshifts we probe, with a decreasing fraction of lower mass galaxies present at all redshifts. This is an example of 'galaxy mass downsizing', and is the result of massive galaxies forming before lower mass ones, and not just simply ending their star formation earlier as in traditional downsizing scenarios, whose effect is seen at z 2. We furthermore show that, although there is a downsizing such that high-mass galaxies are nearer their z = 0 values at high redshift, this turns over at masses M * ∼ 10 10 M ⊙ , such that the lowest mass galaxies are more common than galaxies at slight higher masses, creating a 'dip' in the observed galaxy mass function. We argue that the galaxy assembly process may be driven by different mechanisms at low and high masses, and that the efficiency of the galaxy formation process is lowest at masses M * ~ 10 10 M ⊙ at 1 < z < 3. Finally, we calculate the integrated stellar mass density for the total, blue and red populations. We find the integrated stellar mass density of the total and blue galaxy population is consistent with being constant over z = 1-2, while the red population shows an increase in integrated stellar mass density over the same redshift range.

Hα emitters in z∼ 2 protoclusters: evidence for faster evolution in dense environments

Abstract: This is a study of Hα emitters in two dense galaxy protoclusters surrounding radio galaxies at z∼ 2. We show that the protocluster surrounding MRC 1138−262 contains 14 ± 2 times more Hα candidates than the average field (9σ significance), and the z= 2.35 radio galaxy 4C +10.48 is surrounded by 12 ± 2 times more emitters than the field (5σ), so it is also likely to reside in a dense protocluster environment. We compared these Hα emitters, situated in dense environments, to a control field sample selected from three separate fields forming a total area of 172 arcmin2. We constructed and compared Hα and rest-frame R continuum luminosity functions of the emitters in both environments. The star formation density is on average 13 times greater in the protoclusters than the field at z∼ 2, so the total star formation rate within the central 1.5 Mpc of the protoclusters exceeds 3000 M⊙ yr−1. However, we found no significant difference in the shape of the Hα luminosity functions, implying that environment does not substantially affect the strength of the Hα line from strongly star-forming galaxies. The protocluster emitters are typically 0.8 mag brighter in rest-frame R continuum than field emitters, implying they are twice as massive as their field counterparts at the same redshift. We also show the protocluster galaxies have lower specific star formation rates than field galaxies, meaning the emitters in the dense environments formed more of their stars earlier than the field galaxies. We conclude that galaxy growth in the early Universe was accelerated in dense environments, and that cluster galaxies differed from field galaxies even before the cluster had fully formed.

Galaxy morphology, luminosity, and environment in the SDSS DR7

Abstract: Aims. We study the influence of the environment on the evolution of galaxies by investigating the luminosity function (LF) of galaxies of different morphological types and colours at different environmental density levels. Methods. We construct the LFs separately for galaxies of different morphology (spiral and elliptical) and of different colours (red and blue) using data from the Sloan Digital Sky Survey (SDSS), correcting the luminosities for the intrinsic absorption. We use the global luminosity density field to define different environments, and analyse the environmental dependence of galaxy morphology and colour. The smoothed bootstrap method is used to calculate confidence regions of the derived luminosity functions. Results. We find a strong environmental dependency for the LF of elliptical galaxies. The LF of spiral galaxies is almost environment independent, suggesting that spiral galaxy formation mechanisms are similar in different environments. Absorption by the intrinsic dust influences the bright-end of the LF of spiral galaxies. After attenuation correction, the brightest spiral galaxies are still about 0.5 mag less luminous than the brightest elliptical galaxies, except in the least dense environment, where spiral galaxies dominate the LF at every luminosity. Despite the extent of the SDSS survey, the influence of single rich superclusters is present in the galactic LF of the densest environment.

Galaxy stellar mass functions of different morphological types in clusters, and their evolution between z= 0.8 and 0

Abstract: We present the galaxy stellar mass function and its evolution in clusters from z ∼ 0.8 to the current epoch, based on the WIde-field Nearby Galaxy-cluster Survey (WINGS) (0.04 ≤ z ≤ 0.07), and the ESO Distant Cluster Survey (EDisCS) (0.4 ≤ z ≤ 0.8). We investi- gate the total mass function and find that it evolves noticeably with redshift. The shape at M∗ > 10 11 Mdoes not evolve, but below M∗ ∼ 10 10.8 Mthe mass function at high red- shift is flat, while in the local Universe it flattens out at lower masses. The population of M∗ = 10 10.2 -10 10.8 Mgalaxies must have grown significantly between z = 0.8 and 0. We analyse the mass functions of different morphological types (ellipticals, S0s and late types), and also find that each of them evolves with redshift. All types have proportionally more massive galaxies at high than at low-z, and the strongest evolution occurs among S0 galaxies. Examining the morphology-mass relation (the way the proportion of galaxies of different morphological types changes with galaxy mass), we find it strongly depends on redshift. At both redshifts, ∼40 per cent of the stellar mass is in elliptical galaxies. Another ∼43 per cent of the mass is in S0 galaxies in local clusters, while it is in late types in distant clusters. To explain the observed trends, we discuss the importance of those mechanisms that could shape the mass function. We conclude that mass growth due to star formation plays a crucial role in driving the evolution. It has to be accompanied by infall of galaxies on to clusters, and the mass distribution of infalling galaxies might be different from that of cluster galaxies. However, comparing with high-z field samples, we do not find conclusive evidence for such an environmental mass segregation. Our results suggest that star formation and infall change directly the mass function of late-type galaxies in clusters and, indirectly, that of early-type galaxies through subsequent morphological transformations.

Probing cluster formation under extreme conditions: massive star clusters in blue compact galaxies

Abstract: The numerous and massive young star clusters in blue compact galaxies (BCG) are used to investigate the properties of their hosts. We test whether BCGs follow claimed relations between the cluster ...

Direct observational evidence for a large transient galaxy population in groups at 0.85 < z < 1

Abstract: We introduce our survey of galaxy groups at 0.85 15 members. The dynamical mass estimates are in good agreement with the masses estimated from the X-ray luminosity, with most of the groups having 13 1010.1 M⊙. A few group galaxies inhabit the ‘blue cloud’ that dominates the surrounding field; instead, we find a large and possibly distinct population of galaxies with intermediate colours. The ‘green valley’ that exists at low redshift is instead well populated in these groups, containing ∼30 per cent of the galaxies. These do not appear to be exceptionally dusty galaxies, and about half show prominent Balmer absorption lines. Furthermore, their Hubble Space Telescope morphologies appear to be intermediate between those of red-sequence and blue-cloud galaxies of the same stellar mass. Unlike red-sequence galaxies, most of the green galaxies have a disc component, but one that is smaller and less structured than discs found in the blue cloud. We postulate that these are a transient population, migrating from the blue cloud to the red sequence, with a star formation rate that declines with an exponential time-scale 0.6 < τ < 2 Gyr. Such galaxies may not be exclusive to the group environment, as we find examples also amongst the non-members. However, their prominence among the group galaxy population, and the marked lack of blue, star-forming galaxies, provides evidence that the group environment either directly reduces star formation in member galaxies or at least prevents its rejuvenation during the normal cycle of galaxy evolution.

Evidence for two phases of galaxy formation from radial trends in the globular cluster system of NGC 1407

Abstract: Here we present the colours of individual globular clusters (GCs) around the massive elliptical galaxy NGC 1407 out to a projected galactocentric radius of 140 kpc or 17 galaxy effective radii (Re). Such data are a proxy for the halo metallicity. We find steep, and similar, metallicity 1 gradients of ∼− 0.4 dex dex − for both the blue (metal poor) and red (metal rich) GC subpopulations within 5–8.5 Re (40–70 kpc). At larger radii the mean GC colours (metallicity) are constant. A similar behaviour is seen in a wide-field study of M87’s GC system, and in our own Galaxy. We interpret these radial metallicity trends to indicate an inner region formed by early in situ dissipative processes and an outer halo formed by the ongoing accretion of low-mass galaxies and their GCs. These results provide observational support for the model of galaxy formation whereby massive galaxies form inside-out in two phases. We have also searched the literature for other massive early-type galaxies with reported GC metallicity gradients in their inner regions. No obvious correlation with galaxy mass or environment is found but the sample is currently small.

The x-ray luminous galaxy cluster population at 0.9 < z ≲ 1.6 as revealed by the XMM-Newton Distant Cluster Project*

Abstract: We present the largest sample to date of spectroscopically confirmed x-ray luminous high-redshift galaxy clusters comprising 22 systems in the range as part of the XMM-Newton Distant Cluster Project (XDCP). All systems were initially selected as extended x-ray sources over 76.1?deg2 of non-contiguous deep archival XMM-Newton coverage, of which 49.4?deg2 are part of the core survey with a quantifiable selection function and 17.7?deg2 are classified as ?gold? coverage as the starting point for upcoming cosmological applications. Distant cluster candidates were followed up with moderately deep optical and near-infrared imaging in at least two bands to photometrically identify the cluster galaxy populations and obtain redshift estimates based on the colors of simple stellar population models. We test and calibrate the most promising redshift estimation techniques based on the R?z and z?H colors for efficient distant cluster identifications and find a good redshift accuracy performance of the z?H color out to at least z???1.5, while the redshift evolution of the R?z color leads to increasingly large uncertainties at z???0.9. Photometrically identified high-z systems are spectroscopically confirmed with VLT/FORS?2 with a minimum of three concordant cluster member redshifts. We present first details of two newly identified clusters, XDCP?J0338.5+0029 at z?=?0.916 and XDCP?J0027.2+1714 at z?=?0.959, and investigate the x-ray properties of SpARCS?J003550-431224 at z?=?1.335, which shows evidence for ongoing major merger activity along the line-of-sight. We provide x-ray properties and luminosity-based total mass estimates for the full sample of 22 high-z clusters, of which 17 are at z???1.0 and seven populate the highest redshift bin at z?>?1.3. The median system mass of the sample is M200???2???1014?M?, while the probed mass range for the distant clusters spans approximately (0.7?7)???1014?M?. The majority (>70%) of the x-ray selected clusters show rather regular x-ray morphologies, albeit in most cases with a discernible elongation along one axis. In contrast to local clusters, the z?>?0.9 systems mostly do not harbor central dominant galaxies coincident with the x-ray centroid position, but rather exhibit significant brightest cluster galaxy (BCG) offsets from the x-ray center with a median value of about 50?kpc in projection and a smaller median luminosity gap to the second-ranked galaxy of ?m12???0.3?mag. We estimate a fraction of cluster-associated NVSS 1.4?GHz radio sources of about 30%, preferentially located within 1? from the x-ray center. This value suggests an increase of the fraction of very luminous cluster-associated radio sources by about a factor of 2.5?5 relative to low-z systems. The galaxy populations in z???1.5 cluster environments show first evidence for drastic changes on the high-mass end of galaxies and signs of a gradual disappearance of a well-defined cluster red-sequence as strong star formation activity is observed in an increasing fraction of massive galaxies down to the densest core regions. The presented XDCP high-z sample will allow first detailed studies of the cluster population during the critical cosmic epoch at lookback times of 7.3?9.5?Gyr on the aggregation and evolution of baryons in the cold and hot phases as a function of redshift and system mass.

Discovery of a massive X-ray luminous galaxy cluster at z = 1.579

Abstract: We report on the discovery of a very distant galaxy cluster serendipitously detected in the archive of the XMM-Newton mission, within the scope of the XMM-Newton Distant Cluster Project (XDCP). XMMUJ0044.0-2033 was detected at a high significance level (5σ ) as a compact, but significantly extended source in the X-ray data, with a soft-band flux f (r erg s-1 cm2 . Optical/NIR follow-up observations confirmed the presence of an overdensity of red galaxies matching the X-ray emission. The cluster was spectroscopically confirmed to be at z = 1.579 using ground-based VLT/FORS2 spectroscopy. The analysis of the I − H colour − magnitude diagram shows a sequence of red galaxies with a colour range [3.7 − H bol,40″ ~ 5.8 × 1044 erg s-1 , implying a massive galaxy cluster. This places XMMU J0044.0-2033 at the forefront of massive distant clusters, closing the gap between lower redshift systems and recently discovered proto- and low-mass clusters at z > 1.6.

The Effect of Environment on the Formation of Hα Filaments and Cool Cores in Galaxy Groups and Clusters

Abstract: We present the results of a combined X-ray and Hα study of 10 galaxy groups and 17 galaxy clusters using the Chandra X-ray Observatory and the Maryland Magellan Tunable Filter. We find no difference in the morphology or detection frequency of Hα filaments in groups versus clusters over the mass range 1013 < M 500 < 1015 M ☉. The detection frequency of Hα emission is shown to be only weakly dependent on the total mass of the system at the 52% confidence level. In contrast, we find that the presence of Hα filaments is strongly correlated with both the global (89% confidence level) and core (84%) intracluster medium (ICM) entropy, as well as the X-ray cooling rate (72%). The Hα filaments are therefore an excellent proxy for the cooling ICM. The Hα filaments are more strongly correlated with the cooling properties of the ICM than with the radio properties of the brightest cluster galaxy; this further supports the scenario where these filaments are directly associated with a thermally unstable, rapidly cooling ICM, rather than radio bubbles. The ICM cooling efficiency, defined as the X-ray cooling rate per unit gas mass, is shown to correlate with the total system mass, indicating that groups are more efficient at cooling than clusters. This result implies that, in systems with cool cores, active galactic nucleus feedback scales with the total mass of the system, in agreement with earlier suggestions.

The X-ray luminous galaxy cluster XMMU J1007.4+1237 at z=1.56 - The dawn of starburst activity in cluster cores

Abstract: Context. Observational galaxy cluster studies at z > 1.5 probe the formation of the first massive M > 10 14 M ⊙ dark matter halos, the early thermal history of the hot ICM, and the emergence of the red-sequence population of quenched early-type galaxies. Aims. We present first results for the newly discovered X-ray luminous galaxy cluster XMMUJ1007.4+1237 at z = 1.555, detected and confirmed by the XMM-Newton Distant Cluster Project (XDCP) survey. Methods. We selected the system as a serendipitous weak extended X-ray source in XMM-Newton archival data and followed it up with two-band near-infrared imaging and deep optical spectroscopy. Results. We can establish XMMU J 1007.4+1237 as a spectroscopically confirmed, massive, bona fide galaxy cluster with a bolometric X-ray luminosity of L bol X,500 ≃ (2.1 ± 0.4) x 10 44 erg/s, a red galaxy population centered on the X-ray emission, and a central radio-loud brightest cluster galaxy. However, we see evidence for the first time that the massive end of the galaxy population and the cluster red-sequence are not yet fully in place. In particular, we find ongoing starburst activity for the third ranked galaxy close to the center and another slightly fainter object. Conclusions. At a lookback time of 9.4 Gyr, the cluster galaxy population appears to be caught in an important evolutionary phase, prior to full star-formation quenching and mass assembly in the core region. X-ray selection techniques are an efficient means of identifying and probing the most distant clusters without any prior assumptions about their galaxy content.