Galaxy-Scale Outflows Driven by Active Galactic Nuclei
  We present hydrodynamical simulations of major mergers of galaxies and study
the effects of winds produced by active galactic nuclei (AGN) on interstellar
gas in the AGN's host galaxy. We consider winds with initial velocities ~
10,000 km/s and an initial momentum (energy) flux of ~ tau_w L/c (~ 0.01 tau_w
L), with tau_w ~ 1-10. The AGN wind sweeps up and shock heats the surrounding
interstellar gas, leading to a galaxy-scale outflow with velocities ~ 1000
km/s, peak mass outflow rates comparable to the star formation rate, and a
total ejected gas mass ~ 3 x 10^9 M_sun. Large momentum fluxes, tau_w > 3, are
required for the AGN-driven galactic outflow to suppress star formation and
accretion in the black hole's host galaxy. Less powerful AGN winds (tau_w < 3)
still produce a modest galaxy-scale outflow, but the outflow has little global
effect on the ambient interstellar gas. We argue that this mechanism of AGN
feedback can plausibly produce the high velocity outflows observed in
post-starburst galaxies and the massive molecular and atomic outflows observed
in local ultra-luminous infrared galaxies. Moreover, the outflows from local
ultra-luminous infrared galaxies are inferred to have tau_w ~ 10, comparable to
what we find is required for AGN winds to regulate the growth of black holes
and set the M_BH-sigma relation. We conclude by discussing theoretical
mechanisms that can lead to AGN wind mass-loading and momentum/energy fluxes
large enough to have a significant impact on galaxy formation.
