Growth and activity of black holes in galaxy mergers with varying mass
  ratios
  We study supermassive black holes (BHs) in merging galaxies, using a suite of
hydrodynamical simulations with very high spatial (~10 pc) and temporal (~1
Myr) resolution, where we vary the initial mass ratio, the orbital
configuration, and the gas fraction. (i) We address the question of when and
why, during a merger, increased BH accretion occurs, quantifying gas inflows
and BH accretion rates. (ii) We also quantify the relative effectiveness in
inducing AGN activity of merger-related versus secular-related causes, by
studying different stages of the encounter: the stochastic (or early) stage,
the (proper) merger stage, and the remnant (or late) stage. (iii) We assess
which galaxy mergers preferentially enhance BH accretion, finding that the
initial mass ratio is the most important factor. (iv) We study the evolution of
the BH masses, finding that the BH mass contrast tends to decrease in minor
mergers and to increase in major mergers. This effect hints at the existence of
a preferential range of mass ratios for BHs in the final pairing stages. (v) In
both merging and dynamically quiescent galaxies, the gas accreted by the BH is
not necessarily the gas with $low$ angular momentum, but the gas that $loses$
angular momentum.
