Multi-flavour SMBH seeding and evolution in cosmological environments
  We study the genesis, environment and growth of supermassive black hole
(SMBH) seeds from different formation channels, from PopIII remnants to massive
seeds, modeled within the L-Galaxies semi-analytic code. We run the model on
the merger trees of the Millennium-II simulation (MR-II), as its high halo-mass
resolution (Mvir~10^7 Msun/h) allows to study in a relatively large
cosmological volume (Lbox=100 Mpc/h) the evolution of atomic-cooling halos
where intermediate-mass and heavy seeds are expected to form. We track the
formation of these seeds according to the background and the local variations
of the chemical enrichment and the UV-flux produced by star formation. Not
being able to resolve the first mini-halos, we account for the formation of
PopIII remnants in a sub-grid fashion, using the results of the GQd model. We
find that the descendants of light seeds numerically dominate among the
population of SMBHs at all masses and z. The much rarer intermediate-mass and
heavy seeds form in dense environments where close neighbors provide the
required UV illumination. We also include the formation of heavy seeds in the
mergers of gas-rich massive galaxies, who are very rare in the MR-II volume. We
then track the evolution through gas accretion and mergers of this
multi-flavour population of BH seeds down to z=0. Our model produces a
population of SMBHs whose statistical properties at z=0 meet current
constraints. In the dwarf-mass regime, we predict that the scaling relation
between BH and stellar mass is flatter than in the high-mass range. We also
find that the BH occupation fraction highly depends on the seeding efficiency.
Finally, a fraction of BHs hosted in dwarf galaxies at z=0 never grow since
their formation at z>6. This supports the idea that some local low-mass systems
might harbor central compact objects which are remnant of high-z BH-formation
processes.
