  We investigate black hole-host galaxy scaling relations in cosmological
simulations with a self-consistent black hole growth and feedback model. The
sub-grid accretion model captures the key scalings governing angular momentum
transport from galactic scales down to parsec scales, while our kinetic
feedback implementation enables the injection of outflows with properties
chosen to match observed nuclear outflows. We show that "quasar mode" feedback
can have a large impact on the thermal properties of the intergalactic medium
and the growth of galaxies and massive black holes for kinetic feedback
efficiencies as low as 0.1% relative to the bolometric luminosity. Nonetheless,
our simulations suggest that the black hole-host scaling relations are only
weakly dependent on the effects of black hole feedback on galactic scales,
owing to feedback suppressing the growth of galaxies and massive black holes by
a similar amount. In contrast, the rate at which gravitational torques feed the
central black hole relative to the host galaxy star formation rate governs the
slope and normalization of the black hole-host correlations. Our results
suggest that a common gas supply regulated by gravitational torques is the
primary driver of the observed co-evolution of black holes and galaxies.
