The cosmological analysis of large X-ray galaxy cluster surveys

Large samples of galaxy clusters collected in X-ray observations are able to tightly constrain cosmological scenarios by probing the mass function of large structures and its evolution with time. Current surveys with XMM (XMM-XXL, 50 deg^2 at 10ks depth) and the future eROSITA all-sky survey will deliver sizable samples (10^3-10^5) of objects showing a wide range of signal-to-noise ratios in the X-ray bands. We will present the CR-HR method, particularly suited to capturing the cosmological signal in such samples. By modeling the observed population of cluster properties down to the instrumental level (Count Rates and Hardness Ratios), it self-consistently includes the various model uncertainties and selection biases. We will demonstrate its applicability by presenting the results we obtained from a sample of clusters collected in XMM archival data (X-CLASS, 100 deg^2 at 10-20ks depth). These results will be compared to findings we independently derived from studying the redshift distribution (dn/dz) of a complete cluster sample in the XMM-LSS area (11 deg^2 at 10ks depth), which in particular appeal for a non self-similar evolution in the X-ray Luminosity-Temperature scaling relation and question several detection biases.