EVOLUTION OF IR-SELECTED GALAXIES IN Z~0.4 CLUSTERS

Wide-field optical and near--IR ($JHK$) imaging is presented for two rich galaxy clusters: Abell~370 at $z=0.374$ and Abell~851 (Cl0939+47) at $z=0.407$. Galaxy catalogs selected from the near--IR images are 90\% complete to approximately 1.5 mag below $K^\ast$ resulting in samples with $\sim$100 probable member galaxies per cluster in the central $\sim$2 Mpc. Comparison with $HST$ WFPC images yields subsamples of $\sim$70 galaxies in each cluster with morphological types. Analysis of the complete samples and the $HST$ subsamples shows that the $z\sim 0.4$ E/S0s are bluer than those in the Bower et al.\ (1992) Coma sample in the optical$-K$ color by $0.13$~mag for Abell~370 and by $0.18$~mag for Abell~851. If real, the bluing of the E/S0 populations at moderate redshift is consistent with that calculated from the Bruzual and Charlot (1993) models of passive elliptical galaxy evolution. In both clusters the intrinsic scatter of the known E/S0s about their optical$-K$ color--mag relation is small ($\sim 0.06$ mag) and not significantly different from that of Coma E/S0s as given by Bower et al.\ (1992), indicating that the galaxies within each cluster formed at the same time at an early epoch.Comment: uuencoded gzipped tar file containing latex files of manuscript (42 pages) plus tables (9 pages); figures available by anonymous ftp at ftp://ipac.caltech.edu//pub/pickup/sed ; accepted for publication in the Ap

The K-selected Butcher-Oemler Effect

[abridged] We investigate the Butcher-Oemler effect in a sample of K-selected galaxies in 33 clusters at 0.15 < z < 0.92. We attempt to duplicate the original Butcher-Oemler analysis as closely as possible given the characteristics of our data. We find that the infrared selected blue fractions are lower than those measured in the optical and that the trend with redshift is much weaker. Comparison with optical data in clusters in common with Butcher & Oemler (1984) shows that infrared selection is the primary difference between our study and optically selected samples. We suggest that the Butcher-Oemler effect is in large part due to a population of star-forming low mass galaxies which will evolve into dwarf galaxies. These early results point to the need for larger and deeper infrared samples of cluster galaxies to address this issueComment: 37 pages, 19 figures, ApJ accepted (vol 598 n1

IDCS J1426.5+3508: The Most Massive Galaxy Cluster at z>1.5z > 1.5

We present a deep (100 ks) Chandra observation of IDCS J1426.5+3508, a spectroscopically confirmed, infrared-selected galaxy cluster at $z = 1.75$. This cluster is the most massive galaxy cluster currently known at $z > 1.5$, based on existing Sunyaev-Zel'dovich (SZ) and gravitational lensing detections. We confirm this high mass via a variety of X-ray scaling relations, including $T_X$-M, $f_g$-M, $Y_X$-M and $L_X$-M, finding a tight distribution of masses from these different methods, spanning M$_{500}$ = 2.3-3.3 $\times 10^{14}$ M$_{\odot}$, with the low-scatter $Y_X$-based mass $M_{500,Y_X} = 2.6^{+1.5}_{-0.5} \times 10^{14}$ M$_\odot$. IDCS J1426.5+3508 is currently the only cluster at $z > 1.5$ for which X-ray, SZ and gravitational lensing mass estimates exist, and these are in remarkably good agreement. We find a relatively tight distribution of the gas-to-total mass ratio, employing total masses from all of the aforementioned indicators, with values ranging from $f_{gas,500}$ = 0.087-0.12. We do not detect metals in the intracluster medium (ICM) of this system, placing a 2$\sigma$ upper limit of $Z(r < R_{500}) < 0.18 Z_{\odot}$. This upper limit on the metallicity suggests that this system may still be in the process of enriching its ICM. The cluster has a dense, low-entropy core, offset by $\sim$30 kpc from the X-ray centroid, which makes it one of the few "cool core" clusters discovered at $z > 1$, and the first known cool core cluster at $z > 1.2$. The offset of this core from the large-scale centroid suggests that this cluster has had a relatively recent ($\lesssim$500 Myr) merger/interaction with another massive system.Comment: Minor changes to match accepted version, results unchanged; ApJ in pres

The Massive and Distant Clusters of WISE Survey V: Extended Radio Sources in Massive Galaxy Clusters at z~1

We present the results from a pilot study with the Karl G. Jansky Very Large Array (JVLA) to determine the radio morphologies of extended radio sources and the properties of their host-galaxies in 10 massive galaxy clusters at z~1, an epoch in which clusters are assembling rapidly. These clusters are drawn from a parent sample of WISE-selected galaxy clusters that were cross-correlated with the VLA Faint Images of the Radio Sky at Twenty-Centimeters survey (FIRST) to identify extended radio sources within 1$^{\prime}$ of the cluster centers. Out of the ten targeted sources, six are FR II sources, one is an FR I source, and three sources have undetermined morphologies. Eight radio sources have associated Spitzer data, 75% presenting infrared counterparts. A majority of these counterparts are consistent with being massive galaxies. The angular extent of the FR sources exhibits a strong correlation with the cluster-centric radius, which warrants further investigation with a larger sample.Comment: accepted to Ap

The Massive and Distant Clusters of WISE Survey: SZ effect Verification with the Atacama Compact Array -- Localization and Cluster Analysis

The Massive and Distant Clusters of WISE Survey (MaDCoWS) provides a catalog of high-redshift ($0.7\lesssim z\lesssim 1.5$) infrared-selected galaxy clusters. However, the verification of the ionized intracluster medium, indicative of a collapsed and nearly virialized system, is made challenging by the high redshifts of the sample members. The main goal of this work is to test the capabilities of the Atacama Compact Array (ACA; also known as the Morita Array) Band 3 observations, centered at about 97.5 GHz, to provide robust validation of cluster detections via the thermal Sunyaev-Zeldovich (SZ) effect. Using a pilot sample that comprises ten MaDCoWS galaxy clusters, accessible to ACA and representative of the median sample richness, we infer the masses of the selected galaxy clusters and respective detection significance by means of a Bayesian analysis of the interferometric data. Our test of the "Verification with the ACA - Localization and Cluster Analysis" (VACA LoCA) program demonstrates that the ACA can robustly confirm the presence of the virialized intracluster medium in galaxy clusters previously identified in full-sky surveys. In particular, we obtain a significant detection of the SZ effect for seven out of the ten VACA LoCA clusters. We note that this result is independent of the assumed pressure profile. However, the limited angular dynamic range of the ACA in Band 3 alone, short observational integration times, and possible contamination from unresolved sources limit the detailed characterization of the cluster properties and the inference of the cluster masses within scales appropriate for the robust calibration of mass-richness scaling relations.Comment: 19 pages (including appendices), 14 figures, and 4 tables; accepted for publication in A&