Massive black hole remnants of the first stars in galactic haloes

We investigate the possibility that present-day galactic haloes contain a population of massive black holes (MBHs) that form by hierarchical merging of the BH remnants of the first stars. Some of the MBHs may be large enough or close enough to the centre of the galactic host that they merge within a Hubble time. We estimate to what extent this process could contribute to the mass of the supermassive black holes observed in galactic centres today. Many MBHs will not reach the centre of the main halo, however, but continue to orbit within satellite subhaloes. Using a semi-analytical approach that explicitly accounts for dynamical friction, tidal disruption and encounters with the galactic disc, we follow the dynamics of the satellites and their MBHs and determine the abundance and distribution of MBHs in present-day haloes of various masses. Considering two different accretion scenarios, we also compute the bolometric luminosity function for the MBHs.