The halo occupation distribution of black holes

Abstract

We investigate the halo occupation distribution (HOD) of black holes (BHs) within a hydrodynamic cosmological simulation that directly follows BH's growth. Similar to the HOD of galaxies/subhaloes, we find that the occupation number of a BH can be described by the form NBH∝ 1 + (MHost)α, where α evolves mildly with redshift indicating that a given mass halo (MHost) at low redshift tends to host fewer BHs than at high redshift (as expected as a result of galaxy and BH mergers). We further divide the occupation number into contributions from BHs residing in central and satellite galaxies within a halo. The distribution of MBH within haloes tends to consist of a single massive BH (distributed about a peak mass strongly correlated with MHost) and a collection of relatively low-mass secondary BHs, with a weaker correlation with MHost. We also examine the spatial distribution of BHs within their host haloes and find that they typically follow a power-law radial distribution (i.e. much more centrally concentrated than the subhalo distribution). Finally, we characterize the host mass for which BH's growth is feedback dominated (e.g. star formation quenched). We show that haloes with MHost > 3 × 1012M⊙ have primary BHs that are feedback dominated by z~ 3, with lower mass haloes becoming increasingly more affected at lower redshift. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.