The Palomar Distant Cluster Survey : III. The Colors of the Cluster Galaxies

We present a color analysis of the galaxy populations of candidate clusters of galaxies from the Palomar Distant Cluster Survey (Postman et al.\ 1996). The survey was conducted in two broad band filters that closely match $V$ and $I$ and contains a total of 79 candidate clusters of galaxies, covering an estimated redshift range 0.2 \simless z \simless 1.2. We examine the color evolution in the 57 richest clusters from this survey. The intermediate redshift (0.2 \simless z \simless 0.4) clusters show a distinct locus of galaxy colors in the color--magnitude diagram. This ridge line corresponds well with the expected no--evolution color of present--day elliptical galaxies at these redshifts. In clusters at redshifts of z \simgreat 0.5, this red envelope has shifted bluewards compared to the ``no--evolution'' prediction. By $z \sim 0.8$ there are only a few galaxies which are as red in their rest-frame as present--day ellipticals. The detected evolution is consistent with passive aging of stellar populations formed at redshifts of z \simgreat 2. Though the uncertainties are large, the Butcher--Oemler effect is observed in the Palomar clusters. The fraction of blue galaxies increases with the estimated redshift of the cluster at a 96.2\% confidence level. The measured blue fractions of the intermediate redshift clusters ($f_{b} \sim 0.2 - 0.3$) are consistent with those found previously by Butcher \& Oemler (1984). The trend in the Palomar clusters suggests that $f_{b}$ can be greater than 0.4 in clusters of galaxies at redshifts of z \simgreat 0.6.Comment: Latex, 28 pages, aaspp.sty, 11 figures and epsf.sty included, appended as a uuencoded, gzipped tar file, accepted for publication in the Astronomical Journa

The Tolman Surface Brightness Test for the Reality of the Expansion. III. HST Profile and Surface Brightness Data for Early-Type Galaxies in Three High-Redshift Clusters

Photometric data for 34 early-type galaxies in the three high-redshift clusters Cl 1324+3011 (z = 0.76), Cl 1604+4304 (z = 0.90), and Cl 1604+4321 (z = 0.92), observed with the Hubble Space Telescope (HST) and with the Keck 10-meter telescopes by Oke, Postman & Lubin, are analyzed to obtain the photometric parameters of mean surface brightness, magnitudes for the growth curves, and angular radii at various Petrosian eta radii. The angular radii at eta = 1.3 mag for the program galaxies are all larger than 0.24". All of the galaxies are well resolved at this angular size using HST whose point-spread function is 0.05", half width at half maximum. The data for each of the program galaxies are listed at eta = 1.0, 1.3, 1.5, 1.7, and 2.0 mag. They are corrected by color equations and K terms for the effects of redshift to the rest-frame Cape/Cousins I for Cl 1324+3011 and Cl 1604+4304 and R for Cl 1604+4321. The K corrections are calculated from synthetic spectral energy distributions derived from evolving stellar population models of Bruzual & Charlot which have been fitted to the observed broad-band (BVRI) AB magnitudes of each program galaxy. The listed photometric data are independent of all cosmological parameters. They are the source data for the Tolman surface brightness test made in Paper IV.Comment: 17 pages, 7 figures; accepted for publication in the Astronomical Journa

The Violent Youth of Bright and Massive Cluster Galaxies and their Maturation over 7 Billion Years

In this study we investigate the formation and evolution mechanisms of the brightest cluster galaxies (BCGs) over cosmic time. At high redshift ($z\sim0.9$), we selected BCGs and most massive cluster galaxies (MMCGs) from the Cl1604 supercluster and compared them to low-redshift ($z\sim0.1$) counterparts drawn from the MCXC meta-catalog, supplemented by SDSS imaging and spectroscopy. We observed striking differences in the morphological, color, spectral, and stellar mass properties of the BCGs/MMCGs in the two samples. High-redshift BCGs/MMCGs were, in many cases, star-forming, late-type galaxies, with blue broadband colors, properties largely absent amongst the low-redshift BCGs/MMCGs. The stellar mass of BCGs was found to increase by an average factor of $2.51\pm0.71$ from $z\sim0.9$ to $z\sim0.1$. Through this and other comparisons we conclude that a combination of major merging (mainly wet or mixed) and \emph{in situ} star formation are the main mechanisms which build stellar mass in BCGs/MMCGs. The stellar mass growth of the BCGs/MMCGs also appears to grow in lockstep with both the stellar baryonic and total mass of the cluster. Additionally, BCGs/MMCGs were found to grow in size, on average, a factor of $\sim3$, while their average S\'ersic index increased by $\sim$0.45 from $z\sim0.9$ to $z\sim0.1$, also supporting a scenario involving major merging, though some adiabatic expansion is required. These observational results are compared to both models and simulations to further explore the implications on processes which shape and evolve BCGs/MMCGs over the past $\sim$7 Gyr.Comment: Accepted for publication in MNRA

No Evidence of Quasar-Mode Feedback in a Four-Way Group Merger at z~0.84

We report on the results of a Chandra search for evidence of triggered nuclear activity within the Cl0023+0423 four-way group merger at z ~ 0.84. The system consists of four interacting galaxy groups in the early stages of hierarchical cluster formation and, as such, provides a unique look at the level of processing and evolution already under way in the group environment prior to cluster assembly. We present the number counts of X-ray point sources detected in a field covering the entire Cl0023 structure, as well as a cross-correlation of these sources with our extensive spectroscopic database. Both the redshift distribution and cumulative number counts of X-ray sources reveal little evidence to suggest that the system contains X-ray luminous active galactic nuclei (AGNs) in excess to what is observed in the field population. If preprocessing is under way in the Cl0023 system, our observations suggest that powerful nuclear activity is not the predominant mechanism quenching star formation and driving the evolution of Cl0023 galaxies. We speculate that this is due to a lack of sufficiently massive nuclear black holes required to power such activity, as previous observations have found a high late-type fraction among the Cl0023 population. It may be that disruptive AGN-driven outflows become an important factor in the preprocessing of galaxy populations only during a later stage in the evolution of such groups and structures when sufficiently massive galaxies (and central black holes) have built up, but prior to hydrodynamical processes stripping them of their gas reservoirs.Comment: Published in ApJ

Pushing the Boundaries of the Cl 1604 Supercluster at z~0.9

The Cl 1604 supercluster at z~0.9 is known to contain at least four distinct member clusters, separated in both projection and redshift. In this paper we present deep, multicolor wide-field imaging of a region spanning ~45' on a side, corresponding to 21 h^{-1}_{70} Mpc (physical) at the supercluster redshift. We select galaxies whose colors correspond to those of spectroscopically confirmed cluster members in the r' vs. (r'-i') color-magnitude diagram. Using an adaptive kernel, we generate a map of the projected red galaxy density and identify numerous new candidate clusters which are likely supercluster members. Assuming that all of the density peaks are associated with the supercluster, its transverse size is ~10 h^{-1}_{70} Mpc, which is still significantly smaller than the nearly 93 h^{-1}_{70} Mpc depth in redshift space.Comment: 5 pages, 5 figures. Accepted for publication in AJ. Figures and text updated with correction