Galaxy and hot gas distributions in the z = 0 . 52 galaxy cluster RBS 380 from CHANDRA and NTT observations .

We present CHANDRA X-ray and NTT optical observations of the distant z = 0.52 galaxy cluster RBS380 – the most distant cluster of the ROSAT Bright Source (RBS) catalogue. We find diffuse, non-spherically symmetric X-ray emission with a X-ray luminosity of LX (0.3 − 10 keV) = 1.6 10 erg/s, which is lower than expected from the RBS. The reason is a bright AGN in the centre of the cluster contributing considerably to the X-ray flux. This AGN could not be resolved with ROSAT. In optical wavelength we identify several galaxies belonging to the cluster. The galaxy density is at least 2 times higher than expected for such a X-ray faint cluster, which is another confirmation of the weak correlation between X-ray luminosity and optical richness. The example of the source confusion in this cluster shows how important high-resolution X-ray imaging is for cosmological research.