Breaking the sigma_8-Omega_m degeneracy using the clustering of high-z X-ray AGN

The clustering of X-ray selected AGN appears to be a valuable tool for extracting cosmological information. Using the recent high-precision angular clustering results of ~30000 XMM-Newton soft (0.5-2 keV) X-ray sources (Ebrero et al. 2009), which have a median redshift of $z\sim 1$, and assuming a flat geometry, a constant in comoving coordinates AGN clustering evolution and the AGN bias evolution model of Basilakos et al. (2008), we manage to break the Omega_m-sigma_8 degeneracy. The resulting cosmological constraints are: Omega_m=0.27 (+0.03 -0.05), w=-0.90 (+0.10 -0.16) and sigma_8=0.74 (+0.14 -0.12), while the dark matter host halo mass, in which the X-ray selected AGN are presumed to reside, is M=2.50 (+0.50 -1.50) X 10^13 h^{-1} M(solar). For the constant Lambda model (w=-1) we find Omega_m=0.24 (+- 0.06) and sigma_8=0.83 (+0.11 -0.16), in good agreement with recent studies based on cluster abundances, weak lensing and the CMB, but in disagreement with the recent bulk flow analysis.Comment: Accepted in ApJ. Lett

Precision Cosmology from X-ray AGN clustering

We place tight constraints on the main cosmological parameters of spatially flat cosmological models by using the recent angular clustering results of XMM-{\it Newton} soft (0.5-2 keV) X-ray sources (Ebrero et al. 2009a), which have a redshift distribution with a median of $z\sim 1$. Performing a standard likelihood procedure, assuming a constant in comoving coordinates AGN clustering evolution, the AGN bias evolution model of Basilakos et al. (2008) and the WMAP5 value of $\sigma_8$, we find stringent simultaneous constraints in the ($\Omega_{m},$w) plane, with $\Omega_{m}= 0.26\pm 0.05$, w$=-0.93^{+0.11}_{-0.19}$.Comment: Accepted for publication, MNRAS Lett. in press, 5 pages, 2 figure