Palomar Distant Cluster Survey Research Articles

A Richness Study of 14 Distant X‐Ray Clusters from the 160 Square Degree Survey

We have measured the surface density of galaxies toward 14 X-ray-selected cluster candidates at redshifts z(sub i) 0.46, and we show that they are associated with rich galaxy concentrations. These clusters, having X-ray luminosities of Lx(0.5-2 keV) approx. (0.5 - 2.6) x 10(exp 44) ergs/ sec are among the most distant and luminous in our 160 deg(exp 2) ROSAT Position Sensitive Proportional Counter cluster survey. We find that the clusters range between Abell richness classes 0 and 2 and have a most probable richness class of 1. We compare the richness distribution of our distant clusters to those for three samples of nearby clusters with similar X-ray luminosities. We find that the nearby and distant samples have similar richness distributions, which shows that clusters have apparently not evolved substantially in richness since redshift z=0.5. There is, however, a marginal tendency for the distant clusters to be slightly poorer than nearby clusters, although deeper multicolor data for a large sample would be required to confirm this trend. We compare the distribution of distant X-ray clusters in the L(sub X)-richness plane to the distribution of optically selected clusters from the Palomar Distant Cluster Survey. The optically selected clusters appear overly rich for their X-ray luminosities, when compared to X-ray-selected clusters. Apparently, X-ray and optical surveys do not necessarily sample identical mass concentrations at large redshifts. This may indicate the existence of a population of optically rich clusters with anomalously low X-ray emission, More likely, however, it reflects the tendency for optical surveys to select unvirialized mass concentrations, as might be expected when peering along large-scale filaments.

The Canada-France-Hawaii Telescope Optical PDCS Survey. II. Evolution in the Space Density of Clusters of Galaxies

We present the first dynamical study of the optically selected Palomar Distant Cluster Survey (PDCS). We have measured redshifts for 17 clusters of galaxies in the PDCS and velocity dispersions for a subset of 11. Using our new cluster redshifts, we redetermine the X-ray luminosities and upper limits. We show that 11 of 12 PDCS clusters we observed are real overdensities of galaxies. Most clusters have velocity dispersions appropriate for clusters of galaxies. However, we find a fraction (about one-third) of objects in the PDCS that have velocity dispersions in the range of groups of galaxies (200 ± 100 km s-1) but have richnesses appropriate for clusters of galaxies. Within our survey volume of 31.7 × 104 h-3 Mpc3 (q0 = 0.1) for richness class 2 and greater clusters, we measure the richness function, X-ray luminosity function (using both the detections and upper limits), and the mass function derived from our velocity dispersions. We confirm that the space density, as a function of richness, of clusters of galaxies in the PDCS is ~5 times that of the Abell catalog. Excluding the above fraction of one-third of objects with low velocity dispersions, we measure a space density ~3 times that of the Abell catalog for equivalent mass clusters of galaxies, raising the possibility that the Abell catalog is incomplete. However, our space density estimates are in agreement with other low-redshift, optically selected cluster surveys such as the EDCC, APM, and EDCC2. Our X-ray luminosity function agrees with other measurements based on both X-ray and optically selected samples, so we find that the PDCS does not miss clusters of galaxies that would be found in an X-ray selected survey. Our resulting mass function, centered on 1014 M☉ h-1, agrees with the expectations from such surveys as the Canadian Network for Observational Cosmology cluster survey, though errors on our mass measurements are too large to constrain cosmological parameters. We do show that future machine-based, optically selected surveys can be used to constrain cosmological parameters.

The Canada-France-Hawaii Telescope Optical PDCS Survey (COP). I. The Data

This paper presents and gives the COP (COP: CFHT Optical PDCS; CFHT: Canada-France-Hawaii Telescope; PDCS: Palomar Distant Cluster Survey) survey data. We describe our photometric and spectroscopic observations with the MOS multi-slit spectrograph at the CFH telescope. A comparison of the photometry from the PDCS (Postman et al. 1996) catalogs and from the new images we have obtained at the CFH telescope shows that the different magnitude systems can be cross-calibrated. After identification between the PDCS catalogues and our new images, we built catalogues with redshift, coordinates and V, I and Rmagnitudes. We have classified the galaxies along the lines of sight into field and structure galaxies using a gap technique (Katgert et al. 1996). In total we have observed 18 significant structures along the 10 lines of sight.

Spectroscopic Observations of Optically Selected Clusters of Galaxies from the Palomar Distant Cluster Survey

We have conducted a redshift survey of sixteen cluster candidates from the Palomar Distant Cluster Survey (PDCS) to determine both the density of PDCS clusters and the accuracy of the estimated redshifts presented in the PDCS catalog (Postman et. al. 1996). We find that the matched-filter redshift estimate presented in the PDCS has an error sigma_z = 0.06 in the redshift range 0.1 < z < 0.35 based on eight cluster candidates with three or more concordant galaxy redshifts. We measure the low redshift (0.1 < z < 0.35) space density of PDCS clusters to be 31.3^{+30.5}_{-17.1} * E-06 h^3 Mpc^-3 (68% confidence limits for a Poisson distribution) for Richness Class 1 systems. We find a tentative space density of 10.4^{+23.4}_{-8.4}* E-06 h^3 Mpc^-3 for Richness Class 2 clusters. These densities compare favorably with those found for the whole of the PDCS and support the finding that the space density of clusters in the PDCS is a factor of ~5 above that of clusters in the Abell catalog (Abell 1958; Abell, Corwin, and Olowin 1989). These new space density measurements were derived as independently as possible from the original PDCS analysis and therefore, demonstrate the robustness of the original work. Based on our survey, we conclude that the PDCS matched-filter algorithm is successful in detecting real clusters and in estimating their true redshifts in the redshift range we surveyed.

X-Ray Observations of Distant Optically Selected Clusters

We have measured fluxes or flux limits for 31 of the 79 cluster candidates in the Palomar Distant Cluster Survey (PDCS) using archival ROSAT/PSPC pointed observations. Our X-ray survey reaches a flux limit of $\simeq 3 \times 10^{-14}$ erg s$^{-1}$ cm$^{-2}$ (0.4 - 2.0 keV), which corresponds to luminosities of $L_x\simeq 5 \times 10^{43}$ erg s$^{-1}$ ($H_o$ = 50 km s$^{-1}$ Mpc$^{-1}$, $q_o$ = ${1/2}$), if we assume the PDCS estimated redshifts. Of the 31 cluster candidates, we detect six at a signal-to-noise greater than three. We estimate that $2.9^{+3.3}_{-1.4}$ (90% confidence limits) of these six detections are a result of X-ray emission from objects unrelated to the PDCS cluster candidates. The net surface density of X-ray emitting cluster candidates in our survey, $1.71^{+0.91}_{-2.19}$ clusters deg$^{-2}$, agrees with that of other, X-ray selected, surveys. It is possible, given the large error on our contamination rate, that we have not detected X-ray emission from any of our observed PDCS cluster candidates. We find no statistically significant difference between the X-ray luminosities of PDCS cluster candidates and those of Abell clusters of similar optical richness. This suggests that the PDCS contains objects at high redshift similar to the low redshift clusters in the Abell catalogs. We show that the PDCS cluster candidates are not bright X-ray sources, the average luminosity of the six detected candidates is only $\bar{L_x}=0.9\times10^{44}$ erg s$^{-1}$ (0.4-2.0 keV). This finding is in agreement with previous X-ray studies of high redshift, optically selected, rich clusters of galaxies.

The Palomar Distant Cluster Survey. III. The Colors of the Cluster Galaxy

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 $z \simgreat 0.6$.

The Palomar Distant Cluster Survey. II. The Cluster Profiles

We present a study of the surface density profiles of the clusters of galaxies from the Palomar Distant Cluster Survey (Postman et al. 1996). The survey contains a total of 79 clusters of galaxies, covering the estimated redshift range of $0.2 \simless z \simless 1.2$. We have analyzed the richest clusters in this sample and find that the typical Palomar cluster has a surface density profile of $r^{-1.4}$ ($r \ge 0.10~h^{-1}~{\rm Mpc}$) and a core radius of $0.05~h^{-1}~{\rm Mpc}$. There may be an indication that the slope of the surface density profile steepens with increasing redshift, though the observational uncertainty is at present too large to be conclusive. Our cluster population is inconsistent at a 99.9\% confidence level with a population of azimuthally symmetric clusters.

The Palomar Distant Clusters Survey. I. The Cluster Catalog

view Abstract Citations (330) References (63) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Palomar Distant Clusters Survey. I. The Cluster Catalog Postman, Marc ; Lubin, Lori M. ; Gunn, James E. ; Oke, J. B. ; Hoessel, John G. ; Schneider, Donald P. ; Christensen, Jennifer A. Abstract We present an optical/near-IR selected catalog of 79 clusters distributed over an area of 5.1^deg^ sq. The catalog was constructed from images obtained with the 4-Shooter CCD mosaic camera on the Hale 5 m telescope operating in "scan" mode. The survey, hereafter known as the Palomar distant cluster survey (PDCS), was conducted in two broadband filters that closely resemble V and I. The 4 σ limiting magnitudes for our 300 s exposures are ~23.8(V) and 22.5 (I). A matched filter algorithm was developed and employed to identify the cluster candidates by using positional and photometric data simultaneously. The clusters cover the range 0.2 <~ z <~ 1.2, based on the redshift estimates derived in the cluster detection procedure. An accurate selection function is generated from extensive simulations. We find that the cumulative surface density of clusters with richness class R => 1 is about a factor of 5 higher than the extrapolated density of R => 1 Abell clusters. The PDCS results are consistent with a constant comoving density of clusters to z <~ 0.6, albeit at the above high density level. Constraints on cluster abundances at z > 0.6 will be possible with the acquisition of spectroscopic redshifts for a large subset of these cluster candidates. We also present a supplemental catalog of 28 clusters that do not satisfy all our selection criteria but which include some of the most distant systems detected in the survey. Finding charts for all 107 cluster candidates are provided. Publication: The Astronomical Journal Pub Date: February 1996 DOI: 10.1086/117811 arXiv: arXiv:astro-ph/9511011 Bibcode: 1996AJ....111..615P Keywords: SURVEYS; GALAXIES: CLUSTERING; GALAXIES: DISTANCES AND REDSHIFTS; Astrophysics E-Print: 50 pages of text in uuencoded/compressed format. Figures sent separately. Finding charts not included due to excessive size of the postscript files. Contact postman@stsci.edu for additional information full text sources arXiv | ADS | data products SIMBAD (111) NED (107) Related Materials (2) Part 2: 1996AJ....111.1795L Part 3: 1996AJ....112...23L