The Chandra COSMOS Legacy Survey: Clustering of X-ray selected AGN at 2.9<z<5.5 using photometric redshift Probability Distribution Functions
Abstract
We present the measurement of the projected and redshift space 2-point correlation function (2pcf) of the new catalog of Chandra COSMOS-Legacy AGN at 2.9≤z≤5.5 ( Lbol 1046 erg/s) using the generalized clustering estimator based on phot-z probability distribution functions (Pdfs) in addition to any available spec-z. We model the projected 2pcf estimated using πmax = 200 h-1 Mpc with the 2-halo term and we derive a bias at z3.4 equal to b = 6.6+0.60-0.55, which corresponds to a typical mass of the hosting halos of log Mh = 12.83+0.12-0.11 h-1 M. A similar bias is derived using the redshift-space 2pcf, modelled including the typical phot-z error σz = 0.052 of our sample at z≥2.9. Once we integrate the projected 2pcf up to πmax = 200 h-1 Mpc, the bias of XMM and Chandra COSMOS at z=2.8 used in Allevato et al. (2014) is consistent with our results at higher redshift. The results suggest only a slight increase of the bias factor of COSMOS AGN at z3 with the typical hosting halo mass of moderate luminosity AGN almost constant with redshift and equal to logMh = 12.92+0.13-0.18 at z=2.8 and log Mh = 12.83+0.12-0.11 at z3.4, respectively. The observed redshift evolution of the bias of COSMOS AGN implies that moderate luminosity AGN still inhabit group-sized halos at z3, but slightly less massive than observed in different independent studies using X-ray AGN at z≤2.