Black hole growth and AGN feedback under clumpy accretion
  High-resolution simulations of supermassive black holes in isolated galaxies
have suggested the importance of short (~10 Myr) episodes of rapid accretion
caused by interactions between the black hole and massive dense clouds within
the host. Accretion of such clouds could potentially provide the dominant
source for black hole growth in high-z galaxies, but it remains unresolved in
cosmological simulations. Using a stochastic subgrid model calibrated by
high-resolution isolated galaxy simulations, we investigate the impact that
variability in black hole accretion rates has on black hole growth and the
evolution of the host galaxy. We find this clumpy accretion to more efficiently
fuel high-redshift black hole growth. This increased mass allows for more rapid
accretion even in the absence of high-density clumps, compounding the effect
and resulting in substantially faster overall black hole growth. This increased
growth allows the black hole to efficiently evacuate gas from the central
region of the galaxy, driving strong winds up to ~2500 km/s, producing outflows
~10x stronger than the smooth accretion case, suppressing the inflow of gas
onto the host galaxy, and suppressing the star formation within the galaxy by
as much as a factor of two. This suggests that the proper incorporation of
variability is a key factor in the co-evolution between black holes and their
hosts.
