The RCS 2319+00 supercluster is a massive supercluster at z=0.9 comprising three optically selected, spectroscopically confirmed clusters separated by <3 Mpc on the plane of the sky. This supercluster is one of a few known examples of the progenitors
of present-day massive clusters (10^{15} Msun by z~0.5). We present an extensive spectroscopic campaign carried out on the supercluster field resulting, in conjunction with previously published data, in 1961 high confidence galaxy redshifts. We find 302 structure members spanning three distinct redshift walls separated from one another by ~65 Mpc. The component clusters have spectroscopic redshifts of 0.901, 0.905 and 0.905. The velocity dispersions are consistent with those predicted from X-ray data, giving estimated cluster masses of ~10^{14.5} - 10^{14.9} Msun. The Dressler-Shectman test finds evidence of substructure in the supercluster field and a friends-of-friends analysis identified 5 groups in the supercluster, including a filamentary structure stretching between two cluster cores previously identified in the infrared by Coppin et al. (2012). The galaxy colors further show this filamentary structure to be a unique region of activity within the supercluster, comprised mainly of blue galaxies compared to the ~43-77% red-sequence galaxies present in the other groups and cluster cores. Richness estimates from stacked luminosity function fits results in average group mass estimates consistent with ~10^{13} Msun halos. Currently, 22% of our confirmed members reside in >~10^{13} Msun groups/clusters destined to merge onto the most massive cluster, in agreement with the massive halo galaxy fractions important in cluster galaxy pre-processing in N-body simulation merger tree studies.
We present a submillimetre survey of seven high-z galaxy clusters (0.64<z<1.0) using the Submillimetre Common-User Bolometer Array (SCUBA) at 850 and 450 um. The targets, of similar richness and redshift, are selected from the Red-sequence Cluster Su
rvey (RCS). We use this sample to investigate the apparent excess of submillimetre source counts in the direction of cluster fields compared to blank fields. The sample consists of three galaxy clusters that exhibit multiple optical arcs due to strong gravitational lensing, and a control group of four clusters with no apparent strong lensing. A tentative excess of 2.7-sigma is seen in the number density of submillimetre luminous galaxies (SMGs) within the lensing cluster fields compared to that in the control group. Ancillary observations at radio, mid-infrared, optical, and X-ray wavelengths allow for the identification of counterparts to many of the SMGs. Utilizing photometric redshifts, we conclude that at least three of the galaxies within the lensing fields have redshifts consistent with the clusters and implied infrared luminosities of ~10^12 Lsol. The existence of SMG cluster members may therefore be boosting source counts in the lensing cluster fields, which might be an effect of the dynamical state of those clusters. However, we find that the removal of potential cluster members from the counts analysis does not entirely eliminate the difference between the cluster samples. We also investigate possible occurrences of lensing between background SMGs and lower-z optical galaxies, though further observations are required to make any conclusive claims. Although the excess counts between the two cluster samples have not been unambiguously accounted for, these results warrant caution for interpreting submillimetre source counts in cluster fields and point source contamination for Sunyaev-Zeldovich surveys. [Abridged]
Using wide-field $BVR_cI$ imaging for a sample of 16 intermediate redshift ($0.17 < z < 0.55$) galaxy clusters from the Canadian Network for Observational Cosmology (CNOC1) Survey, we investigate the dependence of cluster galaxy populations and their
evolution on environment. Galaxy photometric redshifts are estimated using an empirical photometric redshift technique and galaxy groups are identified using a modified friends-of-friends algorithm in photometric redshift space.We utilize the red galaxy fraction (fred) to infer the evolutionary status of galaxies in clusters, using both individual galaxies and galaxies in groups. We apply the local galaxy density, sig5, derived using the fifth nearest-neighbor distance, as a measure of local environment, and the cluster-centric radius, rCL, as a proxy for global cluster environment. Our cluster sample exhibits a Butcher-Oemler effect in both luminosity-selected and stellar-mass-selected samples. We find that fred depends strongly on sig5 and rCL, and the Butcher-Oemler effect is observed in all sig5 and rCL bins. However, when the cluster galaxies are separated into rCL bins, or into group and non-group subsamples, the dependence on local galaxy density becomes much weaker. This suggests that the properties of the dark matter halo in which the galaxy resides have a dominant effect on its galaxy population and evolutionary history. We find that our data are consistent with the scenario that cluster galaxies situated in successively richer groups (i.e., more massive dark matter halos) reach a high fred value at earlier redshifts. Associated with this, we observe a clear signature of `pre-processing, in which ... <and more>
We report the discovery of a compact supercluster structure at z=0.9. The structure comprises three optically-selected clusters, all of which are detected in X-rays and spectroscopically confirmed to lie at the same redshift. The Chandra X-ray temper
atures imply individual masses of ~5x10^14 Msun. The X-ray masses are consistent with those inferred from optical--X-ray scaling relations established at lower redshift. A strongly-lensed z~4 Lyman break galaxy behind one of the clusters allows a strong-lensing mass to be estimated for this cluster, which is in good agreement with the X-ray measurement. Optical spectroscopy of this cluster gives a dynamical mass in good agreement with the other independent mass estimates. The three components of the RCS2319+00 supercluster are separated from their nearest neighbor by a mere <3 Mpc in the plane of the sky and likely <10 Mpc along the line-of-sight, and we interpret this structure as the high-redshift antecedent of massive (~10^15 Msun) z~0.5 clusters such as MS0451.5-0305.
We present the evolution of the color-magnitude distribution of galaxy clusters from z = 0.45 to z = 0.9 using a homogeneously selected sample of ~1000 clusters drawn from the Red-Sequence Cluster Survey (RCS). The red fraction of galaxies decreases
as a function of increasing redshift for all cluster-centric radii, consistent with the Butcher-Oemler effect, and suggesting that the cluster blue population may be identified with newly infalling galaxies. We also find that the red fraction at the core has a shallower evolution compared with that at the cluster outskirts. Detailed examination of the color distribution of blue galaxies suggests that they have colors consistent with normal spirals and may redden slightly with time. Galaxies of starburst spectral type contribute less than 5% of the increase in the blue population at high redshift, implying that the observed Butcher-Oemler effect is not caused by a unobscured starbursts, but is more consistent with a normal coeval field population.
We use a statistical sample of ~500 rich clusters taken from 72 square degrees of the Red-Sequence Cluster Survey (RCS-1) to study the evolution of ~30,000 red-sequence galaxies in clusters over the redshift range 0.35<z<0.95. We construct red-sequen
ce luminosity functions (RSLFs) for a well-defined, homogeneously selected, richness limited sample. The RSLF at higher redshifts shows a deficit of faint red galaxies (to M_V=> -19.7) with their numbers increasing towards the present epoch. This is consistent with the `down-sizing` picture in which star-formation ended at earlier times for the most massive (luminous) galaxies and more recently for less massive (fainter) galaxies. We observe a richness dependence to the down-sizing effect in the sense that, at a given redshift, the drop-off of faint red galaxies is greater for poorer (less massive) clusters, suggesting that star-formation ended earlier for galaxies in more massive clusters. The decrease in faint red-sequence galaxies is accompanied by an increase in faint blue galaxies, implying that the process responsible for this evolution of faint galaxies is the termination of star-formation, possibly with little or no need for merging. At the bright end, we also see an increase in the number of blue galaxies with increasing redshift, suggesting that termination of star-formation in higher mass galaxies may also be an important formation mechanism for higher mass ellipticals. By comparing with a low-redshift Abell Cluster sample, we find that the down-sizing trend seen within RCS-1 has continued to the local universe.
