The ROSAT All-Sky Survey: a Catalog of Clusters of Galaxies in a Region of 1 Ster around the South Galactic Pole

Abstract

A field of 1.013 ster in the ROSAT all-sky survey (RASS), centered on the south galactic pole (SGP), has been searched in a systematic, objective manner for clusters of galaxies. The procedure relied on a correlation of the X-ray positions and properties of ROSAT sources with the distribution of galaxies in the COSMOS digitised data base, which was obtained by scanning the plates of the UK Schmidt IIIa-J optical southern sky survey. The study used the second ROSAT survey data base (RASS-2) and included several optical observing campaigns to measure redshifts. The search, a precursor to the larger REFLEX survey of the whole southern sky, reached the detection limits of the RASS and the COSMOS data, and yielded a catalog of 186 clusters in which the lowest flux is 1.5e-12 erg/cm2/s in the 0.1-2.4 keV band. Of these 157 have measured redshifts. Using a limit of 3.0e-12 erg/cm2/s a complete subset of 112 clusters was obtained, of which 110 have measured redshifts. The spatial distribution of the X-ray clusters out to z = 0.15 shows an extension of the Local Supercluster to the Pisces-Cetus supercluster (z<~0.07), and a more distant orthogonal structure at 0.07<z<0.15.