XMM observations of high redshift X-ray clusters and cosmological interpretation

We present the preliminary results of the Ω project, a large XMM program devoted to observe distant SHARC clusters. For the first time a measurement of the L-T evolution with XMM is presented. We found clear evidence for a positive evolution of the L-T relation, in agreement with most previous analysis based on ASCA and Chandra observations. Its cosmological implication is also discussed based on a new analysis of different X-ray surveys: EMSS, RDCS, MACS, SHARC, 160 deg2. It is found that a high matter density model fits remarkably well all these surveys, in agreement with all existing previous analyzes following the same strategy. Concordance models produce far more faint clusters than observed counts. This failure could be the indication of a deviation from the expected scaling of the M-T relation with redshift. However, no signature of such possibility is found in existing data.