A Flux‐limited Sample of Bright Clusters of Galaxies from the Southern Part of the ROSAT All‐Sky Survey: The Catalog and log N –log S

Abstract

We describe the selection of an X-ray flux-limited sample of bright clusters of galaxies in the southern hemisphere, based on the first analysis of the ROSAT All-Sky Survey data (RASS1). The sample is constructed starting from an identification of candidate clusters in RASS1, after which their X-ray fluxes are remeasured using the steepness-ratio technique. This method is better suited than the RASS1 standard algorithm to measuring flux from extended sources. The final sample is count-rate-limited in the ROSAT hard band (0.5-2.0 keV), so that as a result of the distribution of NH, its effective flux limit varies between ∼ 3 and 4 × 10-12 ergs cm-2 s-1 over the selected area. This covers the δ < 2°.5 part of the south Galactic cap region (b