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

Abstract

We present the clustering properties and halo occupation distribution (HOD)\nmodelling of very low redshift, hard X-ray-detected active galactic nuclei\n(AGN) using cross-correlation function measurements with Two-Micron All Sky\nSurvey galaxies. Spanning a redshift range of $0.007 < z < 0.037$, with a\nmedian $z=0.024$, we present a precise AGN clustering study of the most local\nAGN in the Universe. The AGN sample is drawn from the SWIFT/BAT 70-month and\nINTEGRAL/IBIS eight year all-sky X-ray surveys and contains both type I and\ntype II AGN. We find a large-scale bias for the full AGN sample of\n$b=1.04^{+0.10}_{-0.11}$, which corresponds to a typical host dark matter halo\nmass of $M_{\\rm h}^{\\rm typ}=12.84^{+0.22}_{-0.30}\\,h^{-1} M_{\\odot}$. When\nsplit into low and high X-ray luminosity and type I and type II AGN subsamples,\nwe detect no statistically significant differences in the large-scale bias\nparameters. However, there are differences in the small-scale clustering which\nare reflected in the full HOD model results. We find that low and high X-ray\nluminosity AGN, as well as type I and type II AGN, occupy dark matter haloes\ndifferently, with 3.4$\\sigma$ and 4.0$\\sigma$ differences in their mean halo\nmasses, respectively, when split by luminosity and type. The latter finding\ncontradicts a simple orientation-based AGN unification model. As a by-product\nof our cross-correlation approach, we also present the first HOD model of 2MASS\ngalaxies.\n