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 an increase by a factor of ∼ 2 from z = 0 to z ∼ 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 surveys which contain information on the AGN space density at high redshift.