ABSTRACT We report on the discovery of a z = 1.58 mature cluster around the high-redshift radio galaxy 7C 1753+6311, first identified in the Clusters Around Radio-loud active galactic nuclei survey. ...Two-thirds of the excess galaxies within the central 1 Mpc lie on a red sequence with a color that is consistent with an average formation redshift of zf ∼ 3. We show that 80 6% of the red sequence galaxies in the cluster core are quiescent, while the remaining 20% are red due to dusty star formation. We demonstrate that the cluster has an enhanced quiescent galaxy fraction that is three times that of the control field. We also show that this enhancement is mass dependent: 91 9% of the M cluster galaxies are quiescent, compared to only 36 2% of field galaxies, whereas the fraction of quiescent galaxies with lower masses is the same in the cluster and field environments. The presence of a dense core and a well-formed, quiescent red sequence suggest that this is a mature cluster. This means that distant radio galaxies do not solely reside in young, uncollapsed protoclusters, rather they can be found in clusters in a wide range of evolutionary states.
ABSTRACT
Using new and published data, we construct a sample of 160 brightest cluster galaxies (BCGs) spanning the redshift interval 0.03 < z < 1.63. We use this sample, which covers 70 per cent of ...the history of the universe, to measure the growth in the stellar mass of BCGs after correcting for the correlation between the stellar mass of the BCG and the mass of the cluster in which it lives. We find that the stellar mass of BCGs increases by a factor of 1.8 ± 0.3 between z = 0.9 and z = 0.2. Compared to earlier works, our result is closer to the predictions of semi‐analytic models. However, BCGs at z = 0.9, relative to BCGs at z = 0.2, are still a factor of 1.5 more massive than the predictions of these models. Star formation rates in BCGs at z ∼ 1 are generally too low to result in significant amounts of mass. Instead, it is likely that most of the mass build up occurs through mainly dry mergers in which perhaps half of the mass is lost to the intra‐cluster medium of the cluster.
Abstract
We study the mass–richness relation of 116 spectroscopically confirmed massive clusters at 0.4 <
z
< 2 by mining the
Spitzer
archive. We homogeneously measure the richness at 4.5
μ
m for ...our cluster sample within a fixed aperture of 2′ radius and above a fixed brightness threshold, making appropriate corrections for both background galaxies and foreground stars. We have two subsamples, those which have (a) literature X-ray luminosities and (b) literature Sunyaev–Zel’dovich effect masses. For the X-ray subsample we re-derive masses adopting the most recent calibrations. We then calibrate an empirical mass–richness relation for the combined sample spanning more than one decade in cluster mass and find the associated uncertainties in mass at fixed richness to be ±0.25 dex. We study the dependence of the scatter of this relation with galaxy concentration, defined as the ratio between richness measured within an aperture radius of 1 and 2 arcmin. We find that at fixed aperture radius the scatter increases for clusters with higher concentrations. We study the dependence of our richness estimates with depth of the 4.5
μ
m imaging data and find that reaching a depth of at least 4.5 = 21 AB mag is sufficient to derive reasonable mass estimates. We discuss the possible extension of our method to the mid-infrared
WISE
All Sky Survey data and the application of our results to the
Euclid
mission. This technique makes richness-based cluster mass estimates available for large samples of clusters at very low observational cost.
There is a lack of large samples of spectroscopically confirmed clusters and protoclusters at high redshifts, z > 1.5. Discovering and characterizing distant (proto-)clusters is important for ...yielding insights into the formation of large-scale structure and on the physical processes responsible for regulating star-formation in galaxies in dense environments. The Spitzer Planck Herschel Infrared Cluster (SPHerIC) survey was initiated to identify these characteristically faint and dust-reddened sources during the epoch of their early assembly. We present Spitzer/IRAC observations of 82 galaxy (proto-)cluster candidates at 1.3 < zp < 3.0 that were vetted in a two step process: (1) using Planck to select by color those sources with the highest star-formation rates, and (2) using Herschel at higher resolution to separate out the individual red sources. The addition of the Spitzer data enables efficient detection of the central and massive brightest red cluster galaxies (BRCGs). We find that BRCGs are associated with highly significant, extended and crowded regions of IRAC sources which are more overdense than the field. This result corroborates our hypothesis that BRCGs within the Planck–Herschel sources trace some of the densest and actively star-forming proto-clusters in the early Universe. On the basis of a richness-mass proxy relation, we obtain an estimate of their mean masses which suggests our sample consists of some of the most massive clusters at z ≈ 2 and are the likely progenitors of the most massive clusters observed today.
We present the Spitzer Extragalactic Representative Volume Survey (SERVS), an18 deg2
18
deg
2
medium-deep survey at 3.6 and 4.5 μm with the postcryogenicSpitzer Space Telescopeto≈2 μJy
≈
2
μ
...Jy
(AB = 23.1
AB
=
23.1
) depth of five highly observed astronomical fields (ELAIS-N1, ELAIS-S1, Lockman Hole, Chandra Deep Field South, and XMM-LSS). SERVS is designed to enable the study of galaxy evolution as a function of environment from
z ∼ 5
z
∼
5
to the present day and is the first extragalactic survey that is both large enough and deep enough to put rare objects such as luminous quasars and galaxy clusters at
z ≳ 1
z
≳
1
into their cosmological context. SERVS is designed to overlap with several key surveys at optical, near- through far-infrared, submillimeter, and radio wavelengths to provide an unprecedented view of the formation and evolution of massive galaxies. In this article, we discuss the SERVS survey design, the data processing flow from image reduction and mosaicking to catalogs, and coverage of ancillary data from other surveys in the SERVS fields. We also highlight a variety of early science results from the survey.
Recent independent results from numerical simulations and observations have shown that brightest cluster galaxies (BCGs) have increased their stellar mass by a factor of almost 2 between z ∼ 0.9 and ...z ∼ 0.2. The numerical simulations further suggest that more than half this mass is accreted through major mergers. Using a sample of 18 distant galaxy clusters with over 600 spectroscopically confirmed cluster members between them, we search for observational evidence that major mergers do play a significant role. We find a major merger rate of 0.38 ± 0.14 mergers per Gyr at z ∼ 1. While the uncertainties, which stem from the small size of our sample, are relatively large, our rate is consistent with the results that are derived from numerical simulations. If we assume that this rate continues to the present day and that half of the mass of the companion is accreted on to the BCG during these mergers, then we find that this rate can explain the growth in the stellar mass of the BCGs that is observed and predicted by simulations. Major mergers therefore appear to be playing an important role, perhaps even the dominant one, in the build up of stellar mass in these extraordinary galaxies.
We present the stellar mass functions (SMFs) of star-forming and quiescent galaxies from observations of ten rich, redsequence selected, clusters in the Gemini Cluster Astrophysics Spectroscopic ...Survey (GCLASS) in the redshift range 0.86 < z < 1.34. We compare our results with field measurements at similar redshifts using data from a Ks-band selected catalogue of the COSMOS/UltraVISTA field. We construct a Ks-band selected multi-colour catalogue for the clusters in eleven photometric bands covering u-8 mu m, and estimate photometric redshifts and stellar masses using spectral energy distribution fitting techniques. If galaxies in clusters and the field quench their star formation via different mechanisms, these processes have to conspire in such a way that the shapes of the quiescent and star-forming SMF remain similar in these different environments.
We use a sample of 37 of the densest clusters and protoclusters across 1.3 ≤ z ≤ 3.2 from the Clusters Around Radio-Loud AGN (CARLA) survey to study the formation of massive cluster galaxies. We use ...optical i′-band and infrared 3.6 and 4.5 μm images to statistically select sources within these protoclusters and measure their median observed colours; 〈i′ − 3.6〉. We find the abundance of massive galaxies within the protoclusters increases with decreasing redshift, suggesting these objects may form an evolutionary sequence, with the lower redshift clusters in the sample having similar properties to the descendants of the high-redshift protoclusters. We find that the protocluster galaxies have an approximately unevolving observed-frame i′ − 3.6 colour across the examined redshift range. We compare the evolution of the 〈i′ − 3.6〉 colour of massive cluster galaxies with simplistic galaxy formation models. Taking the full cluster population into account, we show that the formation of stars within the majority of massive cluster galaxies occurs over at least 2 Gyr, and peaks at z ∼ 2–3. From the median i′ − 3.6 colours, we cannot determine the star formation histories of individual galaxies, but their star formation must have been rapidly terminated to produce the observed red colours. Finally, we show that massive galaxies at z > 2 must have assembled within 0.5 Gyr of them forming a significant fraction of their stars. This means that few massive galaxies in z > 2 protoclusters could have formed via dry mergers.
Aims. We present the full data set of the spectroscopic campaign of the ESO/GOODS program in the GOODS-South field, obtained with the FORS2 spectrograph at the ESO/VLT. Methods. Objects were selected ...as candidates for VLT/FORS2 observations primarily based on the expectation that the detection and measurement of their spectral features would benefit from the high throughput and spectral resolution of FORS2. The reliability of the redshift estimates is assessed using the redshift-magnitude and color- redshift diagrams, and comparing the results with public data. Results. Including the third part of the spectroscopic campaign (12 masks) to the previous work (26 masks, Vanzella et al. 2005, 2006), 1715 spectra of 1225 individual targets have been analyzed. The actual spectroscopic catalog provides 887 redshift determinations. The typical redshift uncertainty is estimated to be sigma_z simeq 0.001. Galaxies have been selected adopting different color criteria and using photometric redshifts. The resulting redshift distribution typically spans two domains: from z = 0.5 to 2 and z = 3.5 to 6.3. The reduced spectra and the derived redshifts are released to the community through the ESO web page http://www.eso.org/science/goods/.
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