The extended ROSAT-ESO Flux Limited X-ray Galaxy Cluster Survey (REFLEX II) : II. Construction and Properties of the Survey

Abstract

Context. Galaxy clusters provide unique laboratories to study astrophysical processes on large scales and are important probes for cosmology. X-ray observations are currently the best means of detecting and characterizing galaxy clusters. Therefore X-ray surveys for galaxy clusters are one of the best ways to obtain a statistical census of the galaxy cluster population. Aims. In this paper we describe the construction of the REFLEX II galaxy cluster survey based on the southern part of the ROSAT All-Sky Survey. REFLEX II extends the REFLEX I survey by a factor of about two down to a flux limit of 1.8 × 10−12 erg s−1 cm−2 (0.1 - 2.4 keV). Methods. We describe the determination of the X-ray parameters, the process of X-ray source identification, and the construction of the survey selection function. Results. The REFLEX II cluster sample comprises currently 919 objects. A standard selection function is derived for a lower source count limit of 20 photons in addition to the flux limit. The median redshift of the sample is z = 0.102. Internal consistency checks and the comparison to several other galaxy cluster surveys imply that REFLEX II is better than 90% complete with a contamination less than 10%. Conclusions. With this publication we give a comprehensive statistical description of the REFLEX II survey and provide all the complementary information necessary for a proper modelling of the survey for astrophysical and cosmological applications.