The WARPS Survey: VI. Galaxy Cluster and Source Identifications from Phase I

Abstract

We present in catalog form the optical identifications for objects from the first phase of the Wide Angle ROSAT Pointed Survey (WARPS). WARPS is a serendipitous survey of relatively deep, pointed ROSAT observations for clusters of galaxies. The X-ray source detection algorithm used by WARPS is Voronoi Tessellation and Percolation (VTP), a technique which is equally sensitive to point sources and extended sources of low surface brightness. WARPS-I is based on the central regions of 86 ROSAT PSPC fields, covering an area of 16.2 square degrees. We describe here the X-ray source screening and optical identification process for WARPS-I, which yielded 34 clusters at 0.06<z<0.75. Twenty-two of these clusters form a complete, statistically well defined sample drawn from 75 of these 86 fields, covering an area of 14.1 square degrees, with a flux limit of $F (0.5-2.0 keV) = 6.5 \times 10^{-14} erg cm^{-2} s^{-1}}$. This sample can be used to study the properties and evolution of the gas, galaxy and dark matter content of clusters, and to constrain cosmological parameters. We compare in detail the identification process and findings of WARPS to those from other recently published X-ray surveys for clusters, including RDCS, SHARC-Bright, SHARC-south and the CfA 160 deg$^2$ survey.