C. Adami

We present the results of a comprehensive 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 many thousands of artificial clusters with redshifts and luminosities in the range 0.25 < z < 0.95 and 0.5 < LX < 10 × 1044 ergs s-1 (0.5-2.0 keV). We created one standard and 19 varied distribution functions, each of which assumed a different set of cluster, cosmological and operational parameters. The parameters we varied included the values of Ω0, ΩΛ, β, core radius (rc), and ellipticity (e). We also investigated how nonstandard surface brightness profiles (i.e., the Navarro, Frenk, & White, or NFW, model); cooling flows; and the ROSAT pointing target, influence the selection function in the Bright SHARC survey. For our standard set we adopted the parameters used during the derivation of the Bright SHARC Cluster X-Ray Luminosity Function (CXLF), i.e., Ω0 = 1, ΩΛ = 0 and an isothermal β model with β = 0.67, rc = 250 kpc, and e = 0.15. We found that certain parameters have a dramatic effect on our ability to detect clusters, e.g., the presence of a NFW profile or a strong cooling flow profile, or the value of rc and β. Other parameters had very little effect, e.g., the type of ROSAT target and the cluster ellipticity. At distant redshift (z > 0.8), elliptical clusters are significantly easier to detect than spherical ones in the Bright SHARC survey. We show also that all the tested parameters have only a small influence on the computed luminosity of the clusters (recovered luminosity in the text) except the presence of a strong cooling flow. We conclude that the CXLF presented by Nichol et al. in 1999 is robust (under the assumption of standard parameters), but stress the importance of cluster follow-up, by Chandra and XMM, in order to better constrain the morphology of the distant clusters found in the Bright SHARC and other surveys.

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 sq.deg 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 thirty-seven 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<8.3e44 erg/s [0.5-2.0 keV] (assuming Ho = 50 km/s/Mpc and qo=0.5). Twelve of the clusters have redshifts greater than z=0.3, eight of which are at luminosities brighter than Lx=3e44 erg/s. 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. (1994).

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<z<0.95 and 0.5<L_X<10x10^44 erg/s (0.5-2.0 keV). We created 1 standard and 19 varied distribution functions, each of which assumed a different set of cluster, cosmological and operational parameters. The parameters we varied included the values of Omega_0, Omega_Lambda, Beta, core radius and ellipticity. We also investigated how non-standard surface brightness profiles; cooling flows; and the ROSAT pointing target, influence the selection function in the Bright SHARC survey. For our standard set we adopted the parameters used during the derivation of the Bright SHARC Cluster X-ray Luminosity Function (CXLF), i.e. Omega_0=1, Omega_Lambda=0 and an isothermal Beta model with beta=0.67, r_c=250 kpc and e=0.15. We found that certain parameters have a dramatic effect on our ability to detect clusters, e.g. the presence of a NFW profile or a strong cooling flow profile, or the value of r_c and beta. Other parameters had very little effect, e.g. the type of ROSAT target and the cluster ellipticity. We show also that all the tested parameters have only a small influence on the computed luminosity of the clusters except the presence of a strong cooling flow. We conclude that the CXLF presented in Nichol et al. (1999) is robust (under the assumption of standard parameters), but stress the importance of cluster follow-up in order to better constrain the morphology of the distant clusters found in the Bright SHARC and other surveys.

This paper presents the 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 multiobject spectrograph (MOS) at the CFHT. A comparison of the photometry from the PDCS catalogs and from the new images we have obtained at the CFHT shows that the different magnitude systems can be cross-calibrated. After identification between the PDCS catalogs and our new images, we built catalogs with redshift, coordinates, and V_PDCS, I_PDCS, and R_COP magnitudes. We have classified the galaxies along the lines of sight into field and structure galaxies using a gap technique from Katgert et al. In total we have observed 18 significant structures along the 10 lines of sight.

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.

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 sq.deg 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 thirty-seven 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<8.3e44 erg/s [0.5-2.0 keV] (assuming Ho = 50 km/s/Mpc and qo=0.5). Twelve of the clusters have redshifts greater than z=0.3, eight of which are at luminosities brighter than Lx=3e44 erg/s. 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. (1994).Comment: Minor revisions: References updated and typos corrected. Shortened by use of emulateapj.st

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 ≤ L_X ≤ 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 L_X 5 × 10⁴⁴ ergs s^-1 and z 0.7. At L_X > 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, L_X > 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.

We present here initial results on the X-ray Cluster Luminosity Function (XCLF) from the Bright 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 range 0.3 < z < 0.83 (median z = 0.42) and 1.1 < Lx(44) < 8.5 erg/s [0.5-2.0 keV]. We present a preliminary selection function for the Bright SHARC based on Monte Carlo simulations. Using this selection function, we have computed the Bright SHARC XCLF and find it to be fully consistent with a non-evolving XCLF to Lx(44) = 5 erg/s and z = 0.7. At Lx(44) > 5 erg/s, we find evidence for a deficit of clusters compared to that expected from a non-evolving 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. (1999). The statistical significance of this deficit is 96%. To increase the statistical significance of this possible deficit, we have combined the Bright SHARC and the 160 sq. deg. survey of Vikhlinin et al (1998a). This joint survey covers 260 sq. degs. and contains only one confirmed 0.3 < z < 0.7, Lx(44) > 5 erg/s cluster, while we would expect 7.6 such clusters based on the local XCLF (De Grandi et al. 1999). 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.