Enhanced direct collapse due to Lyman alpha feedback
  We assess the impact of trapped Lyman alpha cooling radiation on the
formation of direct collapse black holes (DCBHs). We apply a one-zone chemical
and thermal evolution model, accounting for the photodetachment of H- ions,
precursors to the key coolant H2, by Lyman alpha photons produced during the
collapse of a cloud of primordial gas in an atomic cooling halo at high
redshift. We find that photodetachment of H- by trapped Lyman alpha photons may
lower the level of the H2-dissociating background radiation field required for
DCBH formation substantially, dropping the critical flux by up to a factor of a
few. This translates into a potentially large increase in the expected number
density of DCBHs in the early Universe, and supports the view that DCBHs may be
the seeds for the BHs residing in the centers of a significant fraction of
galaxies today. We find that detachment of H- by Lyman alpha has the strongest
impact on the critical flux for the relatively high background radiation
temperatures expected to characterize the emission from young, hot stars in the
early Universe. This lends support to the DCBH origin of the highest redshift
quasars.
