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

A field of 1.013 sr 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 in the field with the distribution of galaxies in the COSMOS digitized database, which was obtained from scanning the plates of the UK Schmidt IIIa-J optical survey of the southern sky. The study used the second ROSAT survey database (RASS-2) and included several optical observing campaigns to measure cluster redshifts. The search, which is a precursor to the larger REFLEX survey encompassing the whole southern sky, reached the detection limits of both the RASS and the COSMOS data and yielded a catalog of 186 clusters in which the lowest flux is 1.5 × 10^-12 ergs cm^-2 s^-1 in the 0.1-2.4 keV band. Of these 157 have measured redshifts. Using a flux limit of 3.0 × 10^-12 ergs cm^-2 s^-1 a complete subset of 112 clusters was obtained, of which 110 have measured redshifts. The spatial distribution of the X-ray clusters out to a redshift of 0.15 shows an extension of the Local Supercluster to the Pisces-Cetus supercluster (z <∼ 0.07), and an orthogonal structure at higher redshift (0.07 < z < 0.15). This result is consistent with large-scale structure suggested by optical surveys.