The Halo Occupation Distribution Modeling of the X-ray-selected AGNs at 0.6 < z < 2.6 in the COSMOS field

TL;DR

This study measures the clustering of X-ray-selected AGNs at redshifts 1 and 2 in the COSMOS field, revealing insights into their host dark matter halos and satellite populations through HOD modeling.

Contribution

It provides the first detailed Halo Occupation Distribution modeling of X-ray-selected AGNs at these redshifts, highlighting satellite AGN populations and their dependence on halo mass.

Findings

AGN bias increases from z~1 to z~2

Satellite AGNs are prevalent at z~1 across halo masses

Higher halo masses host more satellite AGNs at z~2

Abstract

We conducted precise measurements of Active Galactic Nuclei (AGNs) clustering at $z\sim1$ and $z\sim2$ by measuring the two-point cross-correlation function (CCF) between galaxies and X-ray-selected AGNs, and the two-point auto-correlation 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 {\sl Chandra} COSMOS-Legacy survey catalog. For the AGN samples at $z\sim1$ and $z\sim2$, 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$(M_{\rm typ}/M_{\odot})=11.82\ (11.82;12.12)$ and log$(M_{\rm typ}/M_{\odot})=12.80\ (12.38;13.06)$, respectively. Subsequently, we performed Halo Occupation Distribution (HOD) modeling of X-ray-selected AGNs using the CCF and ACF of galaxies. We have found a significant satellite AGN population at $z\sim 1$ all over the DMH mass ($M_{\rm DMH}$) range occupied by AGNs. While $z\sim 2$ 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 satellite slope in both redshift bins are greater than 0, suggesting tendencies of increasing satellite AGN number with $M_{\rm DMH}$.