How Do Massive Black Holes Get Their Gas?
  We use multi-scale SPH simulations to follow the inflow of gas from galactic
scales to <0.1pc, where the gas begins to resemble a traditional Keplerian
accretion disk. The key ingredients are gas, stars, black holes (BHs),
self-gravity, star formation, and stellar feedback. We use ~100 simulations to
survey a large parameter space of galaxy properties and subgrid models for the
ISM physics. We generate initial conditions for our simulations of galactic
nuclei (<~300pc) using galaxy scale simulations, including both major mergers
and isolated bar-(un)stable disk galaxies. For sufficiently gas-rich,
disk-dominated systems, a series of gravitational instabilities generates large
accretion rates of up to 1-10 M_sun/yr onto the BH (at <<0.1pc); sufficient to
fuel the most luminous quasars. The BH accretion rate is highly time variable,
given fixed conditions at ~kpc. At >~10pc, our simulations resemble the 'bars
within bars' model, but the gas exhibits diverse morphologies, including
spirals, rings, clumps, and bars; their duty cycle is modest, complicating
attempts to correlate BH accretion with nuclear morphology. At ~1-10pc, the
gravitational potential becomes dominated by the BH and bar-like modes are no
longer present. However, the gas becomes unstable to a standing, eccentric disk
or a single-armed spiral mode (m=1), driving the gas to sub-pc scales. Proper
treatment of this mode requires including star formation and the self-gravity
of both the stars and gas. We predict correlations between BHAR and SFR at
different galactic nuclei: nuclear SF is more tightly coupled to AGN activity,
but correlations exist at all scales.
