The RASS-SDSS galaxy cluster survey
  Solid observational evidences indicate a strong dependence of the galaxy formation and evolution on the environment. In order to study in particular the interaction between the intracluster medium and the evolution of cluster galaxies, we have created a large database of clusters of galaxies based on the largest available X-ray and optical surveys: the ROSAT All Sky Survey (RASS), and the Sloan Digital Sky Survey (SDSS). We analyzed the correlation between the total optical and the X-ray cluster luminosity. The resulting correlation of L_X and L_{op} shows a logarithmic slope of 0.6, a value close to the self-similar correlation. We analysed also the cluster mass to light ratio, by finding a significant dependence of M/L on the cluster mass with a logarithmic slope ranging from 0.27 in the i and r bands to 0.22 in the z band. 
P. Popesso, H. Boehringer, W. Voges