Constraints on cosmological and biasing models using active galactic nucleus 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 less than or equal to 0.1) and distant Universe (z similar to 1). To this end we compare the measured ang lar correlation function for bright (Akylas et al.) and faint (Vikhlinin & Forman) 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 the data well. In particular, low-Omega (o) cosmological models (Omega (Lambda) = 1 - Omega (o) = 0.7) that contain either (i) high sigma (mass)(8) = 1.13 value with galaxy merging bias, b(z) proportional to (1 + z)(1.8) or (ii) low sigma (mass)(8) = 0.9 with non-bias, b(z) = 1 best reproduce the AGN clustering results, while tau CDM models with different bias behaviour are ruled out at a high significance level.