The seeds of supermassive black holes and the role of local radiation
  and metal spreading
  We present cosmological hydrodynamical simulations including atomic and
molecular non-equilibrium chemistry, multi-frequency radiative transfer
(0.7-100 eV sampled over 150 frequency bins) and stellar population evolution
to investigate the host candidates of the seeds of supermassive black holes
coming from direct collapse of gas in primordial haloes (direct-collapse black
holes, DCBHs). We consistently address the role played by atomic and molecular
cooling, stellar radiation and metal spreading of C, N, O, Ne, Mg, Si, S, Ca,
Fe, etc. from primordial sources, as well as their implications for nearby
quiescent proto-galaxies under different assumptions for early source
emissivity, initial mass function and metal yields. We find that putative DCBH
host candidates need powerful primordial stellar generations, since common
solar-like stars and hot OB-type stars are neither able to determine the
conditions for direct collapse nor capable of building up a dissociating
Lyman-Werner background radiation field. Thermal and molecular features of the
identified DCBH host candidates in the scenario with very massive primordial
stars seem favourable, with illuminating Lyman-Werner intensities featuring
values of 1-50 J21. Nevertheless, additional non-linear processes, such as
merger events, substructure formation, rotational motions and
photo-evaporation, should inhibit pure DCBH formation in 2/3 of the cases.
Local turbulence may delay gas direct collapse almost irrespectively from other
environmental conditions. The impact of large Lyman-Werner fluxes at distances
smaller than 5 kpc is severely limited by metal pollution.
