Searching for X-ray Galaxy Clusters in the Zone of Avoidance

X-ray galaxy clusters are ideal tracers of the large-scale structure of the Universe. Based on the ROSAT All-Sky Survey we are constructing a sample of the X-ray brightest galaxy clusters for cosmo- logical studies. We have already completed the compilation of a sample of about 1000 clusters in the sky excluding a 40 degree wide band around the galactic plane. We have demonstrated with the southern sample, which is the so far most complete, that we can get reliable statistical measures of the large-scale structure of the Universe to scales in excess of 400h −1 Mpc. With the experience gained in these projects we are ex- tending the search for X-ray galaxy clusters into the Zone-of-Avoidance. We have compiled a sample of 181 good cluster candidates with a well defined completeness of about 70% down to a flux limit of 3 · 10 −12 erg s −1 in the zone with an absorption depth of Av � 2.25. The candidates are definitely identified and redshifts are obtained in an ongoing optical follow-up program.