We attempt to put constraints on different cosmological and biasing models by combining the recent clustering results of X-ray sources in the local ( z \leq 0.1 ) and distant universe ( z \sim 1 ) .
To this end we compare the measured angular correlation function for bright [ 1 ] and faint [ 20 ] ROSAT X-ray sources respectively with those expected in three spatially flat cosmological models .
Taking into account the different functional forms of the bias evolution , we find that there are two cosmological models which match well the data .
In particular , low- \Omega _ { \circ } cosmological models ( \Omega _ { \Lambda } = 0.7 ) that contain either ( i ) high \sigma _ { 8 } ^ { mass } = 1.13 or ( ii ) low \sigma _ { 8 } ^ { mass } = 0.9 respectively with different bias behaviour , best reproduce the AGN clustering results .
While \tau CDM models with different bias behaviour are ruled out at a high significance level .