Black Holes on FIRE: Stellar Feedback Limits Early Feeding of Galactic
  Nuclei
  We introduce massive black holes (BHs) in the Feedback In Realistic
Environments project and perform high-resolution cosmological hydrodynamic
simulations of quasar-mass halos ($M_{\rm halo}(z=2) \approx
10^{12.5}\,\rm{M}_{\odot}$) down to $z=1$. These simulations model stellar
feedback by supernovae, stellar winds, and radiation, and BH growth using a
gravitational torque-based prescription tied to resolved properties of galactic
nuclei. We do not include BH feedback. We show that early BH growth occurs
through short ($\lesssim 1\,$Myr) accretion episodes that can reach or even
exceed the Eddington rate. In this regime, BH growth is limited by bursty
stellar feedback continuously evacuating gas from galactic nuclei, and BHs
remain under-massive relative to the local $M_{\rm BH}$-$M_{\rm bulge}$
relation. BH growth is more efficient at later times, when the nuclear stellar
potential retains a significant gas reservoir, star formation becomes less
bursty, and galaxies settle into a more ordered state, with BHs rapidly
converging onto the scaling relation when the host reaches $M_{\rm bulge} \sim
10^{10}\,\rm{M}_{\odot}$. Our results are not sensitive to the details of the
accretion model so long as BH growth is tied to the gas content within $\sim
100\,$pc of the BH. Our simulations imply that bursty stellar feedback has
strong implications for BH and AGN demographics, especially in the early
Universe and for low-mass galaxies.
