The Halo Occupation Distribution of X-ray-Bright Active Galactic Nuclei: A Comparison with Luminous Quasars

TL;DR

This study models the halo occupation distribution of high-redshift X-ray-bright AGN, revealing they inhabit more massive halos than luminous quasars and have longer active phases, informing future survey designs.

Contribution

It provides the first HOD modeling of X-ray AGN at z~1.2, comparing their halo occupation to luminous quasars and forecasting survey requirements for improved constraints.

Findings

X-ray AGN reside in more massive halos than luminous quasars.

The average duration of the X-ray AGN phase is two orders of magnitude longer than the quasar phase.

A survey area of ~5x10^6 deg^2 is needed for 10% HOD parameter constraints.

Abstract

We perform halo occupation distribution (HOD) modeling of the projected two-point correlation function (2PCF) of high-redshift (z~1.2) X-ray-bright active galactic nuclei (AGN) in the XMM-COSMOS field measured by Allevato et al. The HOD parameterization is based on low-luminosity AGN in cosmological simulations. At the median redshift of z~1.2, we derive a median mass of (1.02+0.21/-0.23)x10^{13} Msun/h for halos hosting central AGN and an upper limit of ~10% on the AGN satellite fraction. Our modeling results indicate (at the 2.5-sigma level) that X-ray AGN reside in more massive halos compared to more bolometrically luminous, optically-selected quasars at similar redshift. The modeling also yields constraints on the duty cycle of the X-ray AGN, and we find that at z~1.2 the average duration of the X-ray AGN phase is two orders of magnitude longer than that of the quasar phase. Our inferred mean occupation function of X-ray AGN is similar to recent empirical measurements with a group catalog and suggests that AGN halo occupancy increases with increasing halo mass. We project the XMM-COSMOS 2PCF measurements to forecast the required survey parameters needed in future AGN clustering studies to enable higher precision HOD constraints and determinations of key physical parameters like the satellite fraction and duty cycle. We find that N^{2}/A~5x10^{6} deg^{-2} (with N the number of AGN in a survey area of A deg^{2}) is sufficient to constrain the HOD parameters at the 10% level, which is easily achievable by upcoming and proposed X-ray surveys.