Gravitational recoils of supermassive black holes in hydrodynamical
  simulations of gas rich galaxies
  We study the evolution of gravitationally recoiled supermassive black holes
(BHs) in massive gas-rich galaxies by means of high-resolution hydrodynamical
simulations. We find that the presence of a massive gaseous disc allows
recoiled BHs to return to the centre on a much shorter timescale than for
purely stellar discs. Also, BH accretion and feedback can strongly modify the
orbit of recoiled BHs and hence their return timescale, besides affecting the
distribution of gas and stars in the galactic centre. However, the dynamical
interaction of kicked BHs with the surrounding medium is in general complex and
can facilitate both a fast return to the centre as well as a significant delay.
The Bondi-Hoyle-Lyttleton accretion rates of the recoiling BHs in our simulated
galaxies are favourably high for the detection of off-centred AGN if kicked
within gas-rich discs -- up to a few per cent of the Eddington accretion rate
-- and are highly variable on timescales of a few 10^7 yrs. In major merger
simulations of gas-rich galaxies, we find that gravitational recoils increase
the scatter in the BH mass -- host galaxy relationships compared to simulations
without kicks, with the BH mass being more sensitive to recoil kicks than the
bulge mass. A generic result of our numerical models is that the clumpy massive
discs suggested by recent high-redshift observations, as well as the remnants
of gas-rich mergers, exhibit a gravitational potential that falls steeply in
the central regions, due to the dissipative concentration of baryons. As a
result, supermassive BHs should only rarely be able to escape from massive
galaxies at high redshifts, which is the epoch where the bulk of BH recoils is
expected to occur.[Abridged]
