B. P. Holden

The Bright SHARC Survey: The Cluster Catalog

We present the Bright SHARC (Serendipitous High-Redshift Archival ROSAT Cluster) Survey, which is an objective search for serendipitously detected extended X-ray sources in 460 deep ROSAT PSPC pointings. The Bright SHARC Survey covers an area of 178.6 deg2 and has yielded 374 extended sources. We discuss the X-ray data reduction, the candidate selection and present results from our on-going optical follow-up campaign. The optical follow-up concentrates on the brightest 94 of the 374 extended sources and is now 97% complete. We have identified 37 clusters of galaxies, for which we present redshifts and luminosities. The clusters span a redshift range of 0.0696< z < 0.83 and a luminosity range of 0.065< LX< 8.31044 ergs s-1 [0.5-2.0 keV] (assuming H0=50 km s-1 Mpc-1 and q0=0.5). Twelve of the clusters have redshifts greater than z=0.3, eight of which are at luminosities brighter than LX=31044 ergs s-1. Seventeen of the 37 optically confirmed Bright SHARC clusters have not been listed in any previously published catalog. We also report the discovery of three candidate ``fossil groups of the kind proposed by Ponman et al. Based on data taken at the European Southern Observatory, Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory, Canada-France-Hawaii, and Apache Point Observatory.

The Southern SHARC Survey: the z = 0.3-0.7 Cluster X-Ray Luminosity Function

We present the z = 0.3-0.7 cluster X-ray luminosity function (XLF) determined from the Southern Serendipitous High-Redshift Archival ROSAT Cluster (SHARC) survey. Over the luminosity range L ~ (0.3-3) × 1044 ergs s-1 (0.5-2.0 keV), the XLF is in close agreement with that of the low-redshift X-ray cluster population. This result greatly strengthens our previous claim of no evolution of the cluster population, at these luminosities, at a median redshift of z=0.44.

A Deficit of High-Redshift, High-Luminosity X-Ray Clusters: Evidence for a High Value of Ωm?

From the Press-Schechter mass function and the empirical X-ray cluster luminosity-temperature (L-T) relation, we construct an X-ray cluster luminosity function that can be applied to the growing number of high-redshift, X-ray cluster luminosity catalogs to constrain cosmological parameters. In this paper, we apply this luminosity function to the Einstein Medium Sensitivity Survey (EMSS) and the ROSAT Brightest Cluster Sample (BCS) luminosity function to constrain the value of ?m. In the case of the EMSS, we find a factor of 4-5 fewer X-ray clusters at redshifts above z = 0.4 than below this redshift at luminosities above LX = 7 ? 1044 ergs s-1 (0.3-3.5 keV), which suggests that the X-ray cluster luminosity function has evolved above L*. At lower luminosities, this luminosity function evolves only minimally, if at all. Using Bayesian inference, we find that the degree of evolution at high luminosities suggests that ?m=0.96+0.36-0.32, given the best-fit L-T relation of Reichart, Castander, & Nichol. When we account for the uncertainty in how the empirical L-T relation evolves with redshift, we find that ?m ? 1.0 ? 0.4. However, it is unclear to what degree systematic effects may affect this and similarly obtained results.

Evolution in the X-Ray Cluster Luminosity Function Revisited

We present new X-ray data taken from the ROSAT Position Sensitive Proportional Counter pointing archive for 21 clusters in the Einstein Extended Medium-Sensitivity Survey (EMSS). We have supplemented these data with new optical follow-up observations found in the literature, and, overall, 32 of the original 67 z > 0.14 EMSS clusters now have new information. Using this revised sample, we find no systematic difference, as a function of X-ray flux, between our measured X-ray cluster fluxes and those in the original EMSS (30% scatter). However, we do detect a marginal correlation between this observed difference in the flux and the redshift of the clusters, with the lower redshift systems having a greater scatter by nearly a factor of 2. We have also determined the X-ray extent of these reobserved EMSS clusters and find that 14 of them have significant extents compared with the ROSAT point-spread function. Combining these data with extended clusters seen in the original EMSS sample, at least 40% of z > 0.14 clusters now have an observed X-ray extent, thus justifying their classification as X-ray clusters. Using our improved EMSS sample, we have redetermined the EMSS X-ray cluster luminosity function as a function of redshift. We have removed potential misclassifications and included our new measurements of the clusters X-ray luminosities and redshifts. We find similar luminosity functions to those originally presented by Henry et al., albeit with two important differences. First, we show that the original low-redshift EMSS luminosity function is insufficiently constrained. Second, the power-law shape of our new determination of the high-redshift EMSS luminosity function (z = 0.3-0.6) has a shallower slope than that seen by Henry et al. We have compared our new EMSS luminosity functions with those recently derived from a nearby sample of X-ray clusters and find that the overall degree of observed luminosity function evolution is mild at best. This is a result of the shallower slope seen in our EMSS high-redshift luminosity function and a more robust low-redshift determination of the X-ray cluster luminosity function from the literature. We have quantified the degree of evolution seen in the X-ray cluster luminosity by using several statistical tests. The most restrictive analysis indicates that our low- and high-redshift EMSS luminosity functions are statistically different at the 95% level. However, other tests indicate that these low- and high-redshift luminosity functions only differ by as little as 1 σ. These data are, therefore, consistent with no evolution in the X-ray cluster luminosity function out to z 0.5.

The Bright SHARC Survey: The X-Ray Cluster Luminosity Function*

We present here initial results on the X-ray cluster luminosity function (XCLF) from the Bright Serendipitous High-Redshift Archival Cluster (SHARC) sample of distant X-ray clusters of galaxies. This sample is 97% complete in its optical identifications and contains 12 X-ray-luminous clusters in the redshift range 0.3 ≤ z ≤ 0.83 (median z = 0.42) and 1.1 × 1044 ≤ LX ≤ 8.3 × 1044 ergs s-1 (0.5-2.0 keV). We present a preliminary selection function for the Bright SHARC Survey based on Monte Carlo simulations. Using this selection function, we have computed the Bright SHARC Survey XCLF and find it to be fully consistent with a nonevolving XCLF to LX 5 × 1044 ergs s-1 and z 0.7. At LX > 5 × 1044 ergs s-1, we find evidence for a deficit of clusters compared to that expected from a nonevolving XCLF. We detect only one such cluster in the redshift range 0.3 ≤ z ≤ 0.7 when we would expect 4.9 clusters based on the local XCLF of De Grandi et al. The statistical significance of this deficit is 96%. To increase the statistical significance of this possible deficit, we have combined the Bright SHARC Survey and the 160 deg2 survey of Vikhlinin et al. This joint survey covers 260 deg2 and contains only one confirmed 0.3 ≤ z ≤ 0.7, LX > 5 × 1044 ergs s-1 cluster, while we would expect 7.6 such clusters based on the local XCLF (De Grandi et al.). The statistical significance of the deficit in this joint survey increases to 99.5%. These results remain preliminary because of incompletenesses in the optical follow-up and uncertainties in the local XCLF.

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

We have conducted a redshift survey of 16 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. We find that the matched-filter redshift estimate presented in the PDCS has an error σz = 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 × 10-6 h3 Mpc-3 (68% confidence limits for a Poisson distribution) for richness class 1 systems. We find a tentative space density of 10.4 × 10-6 h3 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. 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.

The Bright SHARC Survey: The Selection Function and Its Impact on the Cluster X-Ray Luminosity Function

We present the results of a set of simulations designed to quantify the selection function of the Bright SHARC survey for distant clusters. The statistical significance of the simulations relied on the creation of thousands of artificial clusters with redshifts and luminosities in the range 0.25

The CFH 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.

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.