Detection of X-ray clusters of galaxies by matching RASS photons and SDSS galaxies within GAVO^*

Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße 1, 85741 Garching, Germany

Corresponding author: P. Schuecker, peters@mpe.mpg.de

Received: 30 October 2003
Accepted: 3 March 2004

Abstract

A new method for a simultaneous search for clusters of galaxies in X-ray photon maps and optical galaxy maps is described. The merging of X-ray and optical data improves the source identification so that a large amount of telescope time for spectroscopic follow-up can be saved. The method appears thus ideally suited for the analysis of the recently proposed wide-angle X-ray missions like DUO and ROSITA. As a first application, clusters are extracted from the 3rd version of the ROSAT All-Sky Survey and the Early Date Release of the Sloan Digital Sky Survey (SDSS). The time-consuming computations are performed within the German Astrophysical Virtual Observatory (GAVO). On a test area of 140 square degrees, 75 X-ray clusters are detected down to an X-ray flux limit of   in the ROSAT energy band 0.1–2.4 keV. The clusters have redshifts . The survey thus fills the gap between traditional large-area X-ray surveys and serendipitous X-ray cluster searches based on pointed observations, and has the potential to yield about 4000 X-ray clusters after completion of SDSS.