We place tight constraints on the main cosmological parameters of spatially flat cosmological models by using the recent angular clustering results of XMM- 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 } .

Keywords : cosmology : cosmological parameters