The Halo Occupation Distribution Modeling of X-Ray-selected Active Galactic Nuclei at 0.6 < z < 2.6 in the COSMOS Field

Abstract

We conduct precise measurements of active galactic nucleus (AGN) clustering at z ∼ 1 and z ∼ 2 by measuring the two-point cross-correlation function (CCF) between galaxies and X-ray-selected AGNs, and the two-point autocorrelation function (ACF) of galaxies in the COSMOS field, to interpret the CCF results. The galaxy sample was selected from the COSMOS2015 catalog, while the AGN sample was chosen from the Chandra-COSMOS Legacy Survey catalog. For the AGN samples at z ∼ 1 and z ∼ 2, we calculated AGN bias values of b = 1.16 (1.16; 1.31) and b = 2.95 (2.30; 3.55), respectively. These values correspond to typical host dark matter halo (DMH) masses of log( M _typ / M _⊙ ) = 11.82 (11.82; 12.12) and log( M _typ / M _⊙ ) = 12.80 (12.38; 13.06), respectively. Subsequently, we performed halo occupation distribution (HOD) modeling of X-ray-selected AGNs using the CCF and ACF of galaxies. We found a significant satellite AGN population at z ∼ 1 all over the DMH mass ( M _DMH ) range occupied by AGNs, while z ∼ 2 AGNs in our sample are associated with higher-mass DMHs and smaller satellite fractions. The HOD analysis suggests a marginal tendency of increasing satellite slope with redshift, but larger samples are needed to confirm this with sufficient statistical significance. We find that the best-fit values of the satellite slope in both redshift bins are greater than 0, suggesting a tendency of increasing satellite AGN number with M _DMH .

Keywords

• X-ray active galactic nuclei
• Active galactic nuclei