Constraints on Cosmological and Biasing models using AGN clustering

We attempt to put constraints on different cosmological and biasing models by combining the recent clustering results of X-ray sources in the local ($z\le 0.1$) and distant universe ($z\sim 1$). To this end we compare the measured angular correlation function for bright (Akylas et al. 2000) and faint (Vikhlinin & Forman 1995) {\em 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 performs well the data. In particular, low-$\Omega_{\circ}$ cosmological models ($\Omega_{\Lambda}=1-\Omega_{\circ}=0.7$) which contain either (i) high $\sigma_{8}^{\rm mass}=1.13$ value with galaxy merging bias, $b(z) \propto (1+z)^{1.8}$ or (ii) low $\sigma_{8}^{\rm mass}=0.9$ with non-bias, $b(z) \equiv 1$ best reproduce the AGN clustering results. While $\tau$CDM models with different bias behaviour are ruled out at a high significance level.