Self-Regulated Black Hole Growth via Momentum Deposition in Galaxy
  Merger Simulations
  We perform hydrodynamical simulations of major galaxy mergers using new
methods for calculating the growth of massive black holes (BH) in galactic
nuclei and their impact on the surrounding galaxy. We model BH growth by
including a subgrid model for accretion produced by angular momentum transport
on unresolved scales. The impact of the BHs radiation on surrounding gas is
approximated by depositing momentum into the ambient gas, which produces an
outward force away from the BH. We argue that these phenomenological models for
BH growth and feedback better approximate the interaction between the BH and
dense gas in galaxies than previous models. We show that this physics leads to
self-regulated black hole growth: during the peak of activity, the accretion
rate onto the BH is largely determined by the physics of BH feedback, not the
subgrid accretion model. The BH significantly modifies the gas dynamics in the
galactic nucleus (< 300 pc), but does not generate large-scale galactic
outflows. Integrated over an entire galaxy merger, BH feedback has little
effect on the total number of stars formed, but is crucial for setting the BHs
mass.
