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We analyse the intracluster medium (ICM) and circumgalactic medium (CGM) in seven X-ray-detected galaxy clusters using spectra of background quasi-stellar objects (QSOs) (HSTCOS/ STIS), optical spectroscopy of the cluster galaxies (MMT/Hectospec and SDSS), and X-ray imaging/spectroscopy (XMM-Newton and Chandra). First, we report a very low covering fraction of HI absorption in the CGM of these cluster galaxies, fc = 25+25 per cent, to stringent detection limits (N(H I) <10-15 per cent, to stringent detection limits (N(H I) <1013 cm-2). As field galaxies have an HI covering fraction of ~100 per cent at similar radii, the dearth of CGM HI in our data indicates that the cluster environment has effectively stripped or overionized the gaseous haloes of these cluster galaxies. Secondly, we assess the contribution of warm-hot (105-106 K) gas to the ICM as traced by OVI and broad Ly α (BLA) absorption. Despite the high signal-to-noise ratio of our data, we do not detect OVI in any cluster, and we only detect BLA features in the QSO spectrum probing one cluster. We estimate that the total column density of warm-hot gas along this line of sight totals to ~3 per cent of that contained in the hot T > 107 K X-ray emitting phase. Residing at high relative velocities, these features may trace pre-shocked material outside the cluster. Comparing gaseous galaxy haloes from the low-density 'field' to galaxy groups and high-density clusters, we find that the CGM is progressively depleted of HI with increasing environmental density, and the CGM is most severely transformed in galaxy clusters. This CGM transformation may play a key role in environmental galaxy quenching. [ABSTRACT FROM AUTHOR]

We present a sample of 22 blue [(B - V)AB < 0.45], luminous (MB,AB < -18.9), metal-poor galaxies in the 0.69☉ and 1/3 Z☉. We find that galaxies in our sample have comparablemetallicities to other intermediate-redshift samples, but are more metal poor than local systems of similar B-band luminosities and star formation activity. The galaxies here show similar properties to the green peas discovered at z ≃ 0.2-0.3, though our galaxies tend to be slightly less luminous. [ABSTRACT FROM AUTHOR]

We study the dependence of star formation quenching on galaxy mass and environment, in the Sloan Digital Sky Survey (SDSS; z ∼ 0.1) and the All-Wavelength Extended Groth Strip International Survey (AEGIS; z ∼ 1). It is crucial that we define quenching by low star formation rate rather than by red colour, given that one-third of the red galaxies are star forming. We address stellar mass M*, halo mass Mh, density over the nearest N neighbours δN and distance to the halo centre D. The fraction of quenched galaxies appears more strongly correlated with Mh at fixed M* than with M* at fixed Mh, while for satellites quenching also depends on D. We present the M*–Mh relation for centrals at z ∼ 1. At z ∼ 1, the dependence of quenching on M* at fixed Mh is somewhat more pronounced than at z ∼ 0, but the quenched fraction is low (10 per cent) and the haloes are less massive. For satellites, M*-dependent quenching is noticeable at high D, suggesting a quenching dependence on subhalo mass for recently captured satellites. At small D, where satellites likely fell in more than a few Gyr ago, quenching strongly depends on Mh and not on M*. The Mh dependence of quenching is consistent with theoretical wisdom where virial shock heating in massive haloes shuts down accretion and triggers ram-pressure stripping, causing quenching. The interpretation of δN is complicated by the fact that it depends on the number of observed group members compared to N, motivating the use of D as a better measure of local environment. [ABSTRACT FROM AUTHOR]

ABSTRACT We present the Arizona CDFS Environment Survey (ACES), a recently completed spectroscopic redshift survey of the Chandra Deep Field-South (CDFS) conducted using the Inamori-Magellan Areal Camera and Spectrograph on the Magellan-Baade telescope. In total, the survey targeted 7277 unique sources down to a limiting magnitude of RAB = 24.1, yielding 5080 secure redshifts across the ∼30 arcmin × 30 arcmin extended CDFS region. The ACES data set delivers a significant increase to both the spatial coverage and the sampling density of the spectroscopic observations in the field. Combined with previously published spectroscopic redshifts, ACES now creates a highly complete survey of the galaxy population at R < 23, enabling the local galaxy density (or environment) on relatively small scales (∼1 Mpc) to be measured at z < 1 in one of the most heavily studied and data-rich fields in the sky. Here, we describe the motivation, design and implementation of the survey and present a preliminary redshift and environment catalogue. In addition, we utilize the ACES spectroscopic redshift catalogue to assess the quality of photometric redshifts from both the COMBO-17 and Multiwavelength Survey by Yale-Chile imaging surveys of the CDFS. [ABSTRACT FROM AUTHOR]

ABSTRACT Using data drawn from the DEEP2 and DEEP3 Galaxy Redshift Surveys, we investigate the relationship between the environment and the structure of galaxies residing on the red sequence at intermediate redshift. Within the massive (10 < log10( M★/ h−2 M⊙) < 11) early-type population at 0.4 < z < 1.2, we find a significant correlation between local galaxy overdensity (or environment) and galaxy size, such that early-type systems in higher density regions tend to have larger effective radii (by ∼0.5 h−1 kpc or 25 per cent larger) than their counterparts of equal stellar mass and Sérsic index in lower density environments. This observed size-density relation is consistent with a model of galaxy formation in which the evolution of early-type systems at z < 2 is accelerated in high-density environments such as groups and clusters and in which dry, minor mergers (versus mechanisms such as quasar feedback) play a central role in the structural evolution of the massive, early-type galaxy population. [ABSTRACT FROM AUTHOR]

ABSTRACT We present measurements of projected autocorrelation functions wp( rp) for the stellar mass of galaxies and for their light in the U, B and V bands, using data from the third data release of the DEEP2 Galaxy Redshift Survey and the final data release of the Sloan Digital Sky Survey (SDSS). We investigate the clustering bias of stellar mass and light by comparing these to projected autocorrelations of dark matter estimated from the Millennium Simulations (MS) at z= 1 and 0.07, the median redshifts of our galaxy samples. All of the autocorrelation and bias functions show systematic trends with spatial scale and waveband which are impressively similar at the two redshifts. This shows that the well-established environmental dependence of stellar populations in the local Universe is already in place at z= 1. The recent MS-based galaxy formation simulation of reproduces the scale-dependent clustering of luminosity to an accuracy better than 30 per cent in all bands and at both redshifts, but substantially overpredicts mass autocorrelations at separations below about 2 Mpc. Further comparison of the shapes of our stellar mass bias functions with those predicted by the model suggests that both the SDSS and DEEP2 data prefer a fluctuation amplitude of σ8∼ 0.8 rather than the σ8= 0.9 assumed by the MS. [ABSTRACT FROM AUTHOR]

We present a study characterizing the environments of galaxies in the redshift range of based on data from the POWIR near-infrared imaging and DEEP2 spectroscopic redshift surveys, down to a stellar mass of . Galaxy environments are measured in terms of nearest-neighbour densities as well as fixed aperture densities and kinematical and dynamical parameters of neighbour galaxies within a radius of Mpc. We disentangle the correlations between galaxy stellar mass, galaxy colour and galaxy environment, using not only galaxy number densities, but also other environmental characteristics such as velocity dispersion, mean harmonic radius and crossing time. We find that galaxy colour and the fraction of blue galaxies depends very strongly on stellar mass at , while a weak additional dependence on local number densities is in place at lower redshifts . This environmental influence is most visible in the colours of intermediate-mass galaxies , whereas colours of lower- and higher-mass galaxies remain largely unchanged with redshift and environment. At a fixed stellar mass, the colour-density relation almost disappears, while the colour-stellar mass relation is present at all local densities. We find a weak correlation between stellar mass and environment at intermediate redshifts, which contributes to the overall colour-density relation. We furthermore do not find a significant correlation between galaxy colour and virial mass, i.e. parent dark matter halo mass. Galaxy stellar mass thus appears to be the crucial defining parameter for intrinsic galaxy properties such as ongoing star formation and colour. [ABSTRACT FROM AUTHOR]

We use data drawn from the DEEP2 Galaxy Redshift Survey to investigate the relationship between local galaxy density, stellar mass and rest-frame galaxy colour. At , we find that the shape of the stellar mass function at the high-mass end depends on the local environment, with high-density regions favouring more massive systems. Accounting for this stellar mass-environment relation (i.e. working at fixed stellar mass), we find a significant colour-density relation for galaxies with and . This result is shown to be robust to variations in the sample selection and to extend to even lower masses [down to ]. We conclude by discussing our results in comparison to recent works in the literature, which report no significant correlation between galaxy properties and environment at fixed stellar mass for the same redshift and stellar mass domain. The non-detection of environmental dependence found in other data sets is largely attributable to their smaller sample sizes and lower sampling density, as well as systematic effects such as inaccurate redshifts and biased analysis techniques. Ultimately, our results based on DEEP2 data illustrate that the evolutionary state of a galaxy at is not exclusively determined by the stellar mass of the galaxy. Instead, we show that local environment appears to play a distinct role in the transformation of galaxy properties at . [ABSTRACT FROM AUTHOR]

We study filamentary structure in the galaxy distribution at using data from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Redshift Survey and its evolution to using data from the Sloan Digital Sky Survey (SDSS). We trace individual filaments for both surveys using the Smoothed Hessian Major Axis Filament Finder, an algorithm which employs the Hessian matrix of the galaxy density field to trace the filamentary structures in the distribution of galaxies. We extract 33 subsamples from the SDSS data with a geometry similar to that of DEEP2. We find that the filament length distribution has not significantly changed since , as predicted in a previous study using a Λ cold dark matter cosmological N-body simulation. However, the filament width distribution, which is sensitive to the non-linear growth of structure, broadens and shifts to smaller widths for smoothing length-scales of Mpc from to 0.1, in accord with N-body simulations. [ABSTRACT FROM AUTHOR]

We present the discovery of seven X-ray emitting groups of galaxies selected as extended X-ray sources in the 200-ks Chandra coverage of the All-wavelength Extended Groth Strip International Survey (AEGIS). In addition, we report on active galactic nucleus (AGN) activity associated with these systems. For the six extended sources which lie within the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Galaxy Redshift Survey coverage, we identify optical counterparts and determine velocity dispersions. In particular, we find three massive high-redshift groups at , one of which is at , the first X-ray detections of spectroscopically selected DEEP2 groups. We also present a first look at the and scaling relations for high-redshift massive groups. We find that the properties of these X-ray selected systems agree well with the scaling relations of similar systems at low redshift, although there are X-ray undetected groups in the DEEP2 catalogue with similar velocity dispersions. The other three X-ray groups with identified redshifts are associated with lower mass groups at and together form part of a large structure or ‘supergroup’ in the southern portion of the AEGIS field. Similar to other X-ray-luminous groups, all of the low-redshift systems are centred on massive elliptical galaxies, and all of the high-redshift groups have likely central galaxies or galaxy pairs. Interestingly, the central galaxies in the highest redshift system show indications of ongoing star formation. All of the central group galaxies host X-ray point sources, radio sources and/or show optical AGN emission. Particularly interesting examples of central AGN activity include a bent-double radio source plus X-ray point source at the centre of a group at , extended radio and double X-ray point sources associated with the central galaxy in the lowest redshift group at , and a bright green valley galaxy (part of a pair) in the group which shows optical AGN emission lines. [ABSTRACT FROM AUTHOR]

Using galaxy samples drawn from the Sloan Digital Sky Survey and the DEEP2 Galaxy Redshift Survey, we study the relationship between star formation and environment at and 1. We estimate the total star formation rate (SFR) and specific star formation rate (sSFR) for each galaxy according to the measured [O ii]λ 3727 Å nebular line luminosity, corrected using empirical calibrations to match more robust SFR indicators. Echoing previous results, we find that in the local Universe star formation depends on environment such that galaxies in regions of higher overdensity, on average, have lower SFRs and longer star formation time-scales than their counterparts in lower density regions. At , we show that the relationship between sSFR and environment mirrors that found locally. However, we discover that the relationship between total SFR and overdensity at is inverted relative to the local relation. This observed evolution in the SFR–density relation is driven, in part, by a population of bright, blue galaxies in dense environments at . This population, which lacks a counterpart at , is thought to evolve into members of the red sequence from to ∼0. Finally, we conclude that environment does not play a dominant role in the cosmic star formation history at : the dependence of the mean galaxy SFR on local galaxy density at constant redshift is small compared to the decline in the global SFR space density over the last 7 Gyr. [ABSTRACT FROM AUTHOR]

We explore the behaviour of the blue galaxy fraction over the redshift range in the DEEP2 Survey, both for field galaxies and for galaxies in groups. The primary aim is to determine the role that groups play in driving the evolution of galaxy colour at high z. In pursuing this aim, it is essential to define a galaxy sample that does not suffer from redshift-dependent selection effects in colour–magnitude space. We develop four such samples for this study: at all redshifts considered, each one is complete in colour–magnitude space, and the selection also accounts for evolution in the galaxy luminosity function. These samples will also be useful for future evolutionary studies in DEEP2. The colour segregation observed between local group and field samples is already in place at z∼ 1: DEEP2 groups have a significantly lower blue fraction than the field. At fixed z, there is also a correlation between blue fraction and galaxy magnitude, such that brighter galaxies are more likely to be red, both in groups and in the field. In addition, there is a negative correlation between blue fraction and group richness. In terms of evolution, the blue fraction in groups and the field remains roughly constant from to 1, but beyond this redshift the blue fraction in groups rises rapidly with z, and the group and field blue fractions become indistinguishable at z∼ 1.3. Careful tests indicate that this effect does not arise from known systematic or selection effects. To further ensure the robustness of this result, we build on previous mock DEEP2 catalogues to develop mock catalogues that reproduce the colour–overdensity relation observed in DEEP2 and use these to test our methods. The convergence between the group and field blue fractions at z∼ 1.3 implies that DEEP2 galaxy groups only became efficient at quenching star formation at z∼ 2; this result is broadly consistent with other recent observations and with current models of galaxy evolution and hierarchical structure growth. [ABSTRACT FROM AUTHOR]

Using a sample of 19 464 galaxies drawn from the DEEP2 Galaxy Redshift Survey, we study the relationship between galaxy colour and environment at . We find that the fraction of galaxies on the red sequence depends strongly on local environment out to , being larger in regions of greater galaxy density. At all epochs probed, we also find a small population of red, morphologically early-type galaxies residing in regions of low measured overdensity. The observed correlations between the red fraction and local overdensity are highly significant, with the trend at detected at a greater than 5σ level. Over the entire redshift regime studied, we find that the colour–density relation evolves continuously, with red galaxies more strongly favouring overdense regions at low z relative to their red-sequence counterparts at high redshift. At , the red fraction only weakly correlates with overdensity, implying that any colour dependence to the clustering of galaxies at that epoch must be small. Our findings add weight to existing evidence that the build-up of galaxies on the red sequence has occurred preferentially in overdense environments (i.e. galaxy groups) at . Furthermore, we identify the epoch at which typical galaxies began quenching and moved on to the red sequence in significant number. The strength of the observed evolutionary trends at suggests that the correlations observed locally, such as the morphology–density and colour–density relations, are the result of environment-driven mechanisms (i.e. ‘nurture’) and do not appear to have been imprinted (by ‘nature’) upon the galaxy population during their epoch of formation. [ABSTRACT FROM AUTHOR]

We study the mean environment of galaxies in the DEEP2 Galaxy Redshift Survey as a function of rest-frame colour, luminosity, and [O ii] 3727 Å equivalent width. The local galaxy overdensity for >14 000 galaxies at is estimated using the projected third-nearest-neighbour surface density. Of the galaxy properties studied, mean environment is found to depend most strongly on galaxy colour; all major features of the correlation between mean overdensity and rest-frame colour observed in the local universe were already in place at . In contrast to local results, we find a substantial slope in the mean dependence of environment on luminosity for blue, star forming galaxies at , with brighter blue galaxies being found on average in regions of greater overdensity. We discuss the roles of galaxy clusters and groups in establishing the observed correlations between environment and galaxy properties at high redshift, and we also explore the evidence for a ‘downsizing of quenching’ from to ∼0. Our results add weight to existing evidence that the mechanism(s) that result in star formation quenching are efficient in group environments as well as clusters. This work is the first of its kind at high redshift and represents the first in a series of papers addressing the role of environment in galaxy formation at . [ABSTRACT FROM AUTHOR]