Catalog of Rosat Clusters

We present a catalog of 200 clusters of galaxies serendipitously detected in 647 ROSAT PSPC high Galactic latitude pointings covering 158 square degrees. This is one of the largest X-ray selected cluster samples, comparable in size only to the ROSAT All-Sky Survey sample of nearby clusters (Ebeling et al. 1997). We detect clusters in the inner 17.5 of the ROSAT PSPC field of view using the spatial extent of their X-ray emission. Fluxes of detected clusters range from 1.6×10−14 to 8×10−12 ergs s−1 cm−2 in the 0.5–2 keV energy band. X-ray luminosities range from 1042 erg s−1, corresponding to very poor groups, to ∼ 5× 1044 erg s−1, corresponding to rich clusters. The cluster redshifts range from z = 0.015 to z > 0.5. The catalog lists X-ray fluxes, core-radii, spectroscopic redshifts for 73 clusters and photometric redshifts for the remainder. Our detection method, optimized for finding extended sources in the presence of source confusion, is described in detail. Selection effects necessary for a statistical analysis of the cluster sample are comprehensively studied by Monte-Carlo simulations. We have optically confirmed 200 of 223 X-ray sources as clusters of galaxies. Of the remaining 23 sources, 18 are likely false detections arising from blends of unresolved point X-ray sources, and for 5 we have not obtained deep CCD images. Above a flux of 2×10−13 ergs s−1 cm−2, 98% of extended X-ray sources are optically confirmed clusters. The logN − logS relation for clusters derived from our catalog shows excellent agreement with counts of bright clusters derived from the Einstein Extended Medium Sensitivity Survey (Henry et al. 1992) and ROSAT All-Sky Survey (Ebeling et al. 1997). At fainter fluxes, our logN − logS relation agrees with the smaller-area WARPS survey (Jones et al. 1998). Our cluster counts appear to be systematically higher than those from a 50 deg2 survey of Rosati et al. (1998). In particular, at a flux of 2×10−13 ergs s−1 cm−2, we find a surface density of clusters of 0.57± 0.07 per square degree, which is a factor of 1.3 more than found by Rosati et al. This difference is marginally significant at the ∼ 2 sigma level. The large area of our survey makes it possible to study the evolution of the X-ray luminosity function in the high luminosity range inaccessible with other, smaller area ROSAT surveys. Subject headings: galaxies: clusters: general — surveys — X-rays: galaxies