Spatial clustering and halo occupation distribution modeling of local AGN via cross-correlation measurements with 2MASS galaxies

Abstract

We present the clustering properties and halo occupation distribution (HOD) modeling of very low redshift, hard X-ray-detected active galactic nuclei (AGN) using cross-correlation function measurements with 2MASS galaxies. Spanning a redshift range of \(0.007 < z < 0.037\), with a median \(z=0.024\), we present a precise AGN clustering study of the most local AGN in the Universe. The AGN sample is drawn from the SWIFT/BAT 70-Month and INTEGRAL/IBIS 8-Year all-sky X-ray surveys and contains both type I and type II AGN. We find a large-scale bias for the full AGN sample of \(b=1.04^{+0.10}_{-0.11}\), which corresponds to a typical host dark matter halo mass of \(M_{\rm h}^{\rm typ}=12.84^{+0.22}_{-0.30}\,h^{-1} M_{\odot}\). When split into low and high X-ray luminosity and type I and type II AGN subsamples, we detect no statistically significant differences in the large-scale bias parameters. However, there are differences in the small-scale clustering which are reflected in the full HOD model results. We find that low and high X-ray luminosity AGN, as well as type I and type II AGN, occupy dark matter halos differently, with 3.4\(\sigma\) and 4.0\(\sigma\) differences in their mean halo masses, respectively, when split by luminosity and type. The latter finding contradicts a simple orientation-based AGN unification model. As a by-product of our cross-correlation approach, we also present the first HOD model of 2MASS galaxies.