info:eu-repo/semantics/article
Clustering, Bias and the Accretion Mode of X-ray selected AGN
Autor
Manolis Plionis
Resumen
We present the spatial clustering properties of 1466 X-ray selected AGN compiled from the Chandra CDF-N, CDF-S, eCDF-S, COSMOS and AEGIS fields in the 0.5−8 keV band. The X-ray sources span the redshift interval 0 < z < 3 and have a median value of ž = 0.976. We employ the projected two-point correlation function to infer the spatial clustering and find a clustering length of r₀ = 7.2 ± 0.6h⁻¹ Mpc and a slope of γ = 1.48 ± 0.12, which corresponds to a bias of b(ž) = 2.26±0.16. Using two different halo bias models, we consistently estimate an average dark-matter host halo mass of Mh ⋍ 1.3(±0.3) × 10¹³ h⁻¹M⨀. The Xray AGN bias and the corresponding dark-matter host halo mass, are significantly higher than the corresponding values of optically selected AGN (at the same redshifts). The redshift evolution of the X-ray selected AGN bias indicates, in agreement with other recent studies, that a unique dark-matter halo mass does not fit well the bias at all the different redshifts probed. Furthermore, we investigate if there is a dependence of the clustering strength on X-ray luminosity. To this end we consider only 650 sources around z ~ 1 and we apply a procedure to disentangle the dependence of clustering on redshift. We find indications for a positive dependence of the clustering length on X-ray luminosity, in the sense that the more luminous sources have a larger clustering length and hence a higher dark-matter halo mass. In detail we find for an average luminosity difference of δ log₁₀ Lx ⋍ 1 a halo mass difference of a factor of ~3. These findings appear to be consistent with a galaxy-formation model where the gas accreted onto the supermassive black hole in intermediate luminosity AGN comes mostly from the hot-halo atmosphere around the host galaxy.
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