Constraining halo occupation properties of X-ray AGNs using clustering of Chandra sources in the Bootes survey region

TL;DR

This study measures the spatial clustering of X-ray selected AGNs from Chandra in the Bootes survey, revealing their typical halo environments and supporting merger-driven quasar activity models.

Contribution

It provides one of the most precise clustering measurements of X-ray AGNs across a wide redshift range, constraining their halo occupation and evolution.

Findings

AGNs are mainly located at dark matter halo centers with Vmax>320 km/s.

Clustering length shows no significant redshift evolution.

Low satellite galaxy fraction among AGN host halos.

Abstract

We present one of the most precise measurement to date of the spatial clustering of X-ray selected AGNs using a sample derived from the Chandra X-ray Observatory survey in the Bootes field. The real-space two-point correlation function over a redshift interval from z=0.17 to z~3 is well described by the power law, xi(r)=(r/r0)^-gamma, for comoving separations r<~20h^-1 Mpc. We find gamma=1.84+-0.12 and r0 consistent with no redshift trend within the sample (varying between r0=5.5+-0.6 h^-1 Mpc for <z>=0.37 and r0=6.9+-1.0 h^-1 Mpc for <z>=1.28). Further, we are able to measure the projections of the two-point correlation function both on the sky plane and in the line of sight. We use these measurements to show that the Chandra/Bootes AGNs are predominantly located at the centers of dark matter halos with the circular velocity Vmax>320 km/s or M_200 > 4.1e12 h^-1 Msun, and tend to avoid satellite galaxies in halos of this or higher mass. The halo occupation properties inferred from the clustering properties of Chandra/Bootes AGNs --- the mass scale of the parent dark matter halos, the lack of significant redshift evolution of the clustering length, and the low satellite fraction --- are broadly consistent with the Hopkins et al. scenario of quasar activity triggered by mergers of similarly-sized galaxies.