Testing current synthesis models of the X-ray background

We present synthesis models of the X-ray background where the available X-ray observational constraints are used to derive information on the AGN population properties . We show the need for luminous X-ray absorbed AGNs, the QSO2s. in reproducing the 2.10 keV source counts at relatively bright fluxes. We compare a model where the evolution of absorbed AGNs is faster than that of unabsorbed ones, with a standard model where absorbed and unabsorbed AGNs evolve at the same rate. It is: found that all increase by a factor of similar to 2 from z = 0 to z similar to 1.3 in the ratio between absorbed and unabsorbed AGNs would provide a significant improvement in the data description. Finally, we make predictions on the AGNs to be observed in deep X-ray survey which contain information oil the AGN spare density at high redshift.