Bulge-driven Fueling of Seed Black Holes
  We examine radiation-regulated accretion onto intermediate-mass and massive
black holes (BHs) embedded in a bulge component. Using spherically symmetric
one-dimensional radiation-hydrodynamics simulations, we track the growth of BHs
accreting from a cold, neutral gas reservoir with temperature T=10^4 K. We find
that the accretion rate of BHs embedded in bulges is proportional to
r_{B,eff}/r_B, where r_{B,eff} is the increased effective Bondi radius that
includes the gravitational potential of the bulge, and r_B is the Bondi radius
of the BH. The radiative feedback from the BH suppresses the cold accretion
rate to ~1 percent of the Bondi rate when a bulge is not considered. However,
we find that the BH fueling rate increases rapidly when the bulge mass M_bulge
is greater than the critical value of 10^6 M_sun and is proportional to
M_bulge. Since the critical bulge mass is independent of the central BH mass
M_{BH}, the growth rate of BHs with masses of 10^2, 10^4, and 10^6 M_sun
exhibits distinct dependencies on the bulge-to-BH mass ratio. Our results imply
that light seed BHs (<= 10^2 M_sun) which might be the remnants of the Pop III
stars, cannot grow through accretion coevally with the early assembly of the
bulge of the host galaxies until the bulge reaches the critical mass. However,
massive BH seeds (>= 10^5 M_sun) that may form via direct collapse, are more
likely to be embedded in a supercritical bulge and thus can grow efficiently
coupling to the host galaxies and driving the early evolution of the
M_{BH}-$\sigma$ relationship.
