From the Earliest Seeds to Today’s Supermassive Black Holes

Abstract

I review scenarios for the assembly of supermassive black holes (MBHs) at the center of galaxies that trace their hierarchical build-up far up in the dark matter halo "merger tree". Monte Carlo realizations of the merger hierarchy in a LCDM cosmology, coupled to semi-analytical recipes, are a powerful tool to follow the merger history of halos and the dynamics and growth of the MBHs they host. X-ray photons from miniquasars powered by intermediate-mass "seed" holes may permeate the universe more uniformly than EUV radiation, make the low-density diffuse intergalactic medium warm and weakly ionized prior to the epoch of reionization breakthrough, and set an entropy floor. The spin distribution of MBHs is determined by gas accretion, and is predicted to be heavily skewed towards fast-rotating Kerr holes, to be already in place at early epochs, and not to change significantly below redshift 5. Decaying MBH binaries may shape the innermost central regions of galaxies and should be detected in significant numbers by LISA.