A Serendipitous Deep Cluster Survey from ROSAT--PSPC pointed observations

Abstract

We present a deep X-ray selected sample of galaxy clusters which has been created from a serendipitous search in ROSAT-PSPC deep pointed observations at high galactic latitude. This survey, hereafter known as the ROSAT Deep Cluster Survey (RDCS), is being carried out utilizing a wavelet-based detection algorithm which, unlike other detection methods, is not biased against extended, low surface brightness sources. It is a flux-diameter limited sample that extends the X-ray flux limit of previous cluster surveys by more than one order of magnitude ($F_X \ge 1\cdot 10^{-14}\rm erg\, cm^{-2}s^{-1}$). The first results of the on-going optical follow-up program indicate a high success rate of identification. At the present, 38 clusters out of 80 candidates have been identified on a 26 deg$^2$ surveyed area. Recently measured redshifts confirm the nature of these systems as low-moderate redshift groups ($z\simeq 0.2-0.3$) and intermediate to high redshift clusters ($z\simeq 0.4-0.7$). We show X-ray and optical images of several clusters identified to date, discuss the X-ray properties of the sample and present preliminary results on the redshift distribution. The final sample will include $\sim 100$ clusters covering and area of $\sim 40$ deg$^2$.