Consequences of Mechanical and Radiative Feedback from Black Holes in
  Disc Galaxy Mergers
  We study the effect of AGN mechanical and radiation feedback on the formation
of bulge dominated galaxies via mergers of disc galaxies. The merging galaxies
have mass-ratios of 1:1 to 6:1 and include pre-existing hot gaseous halos to
properly account for the global impact of AGN feedback. Using smoothed particle
hydrodynamics simulation code (GADGET-3) we compare three models with different
AGN feedback models: (1) no black hole and no AGN feedback; (2) thermal AGN
feedback; and (3) mechanical and radiative AGN feedback. The last model is
motivated by observations of broad line quasars which show winds with initial
velocities of $v_w \ge$ 10,000 km/s and also heating associated with the
central AGN X-ray radiation. The primary changes in gas properties due to
mechanical AGN feedback are lower thermal X-ray luminosity from the final
galaxy - in better agreement with observations - and galactic outflows with
higher velocity $\sim 1000$ km/s similar to recent direct observations of
nearby merger remnants. The kinetic energy of the outflowing gas is a factor of
$\sim$ 20 higher than in the thermal feedback case. All merger remnants with
momentum-based AGN feedback with $v_w \sim 10,000$ km/s and $\epsilon_w=2
\times 10^{-3}$, independent of their progenitor mass-ratios, reproduce the
observed relations between stellar velocity dispersion and black hole mass
($M_{\rm bh} - \sigma$) as well as X-ray luminosity ($L_X - \sigma$) with
$10^{37.5}$ erg/s $\lesssim L_X (0.3-8~{\rm keV}) \lesssim 10^{39.2}$ erg/s for
velocity dispersions in the range of 120 km/s $\lesssim \sigma \lesssim$ 190
km/s. In addition, the mechanical feedback produces a much greater AGN
variability. We also show that gas is more rapidly and impulsively stripped
from the galactic centres driving a moderate increase in galaxy size and
decrease in central density with the mechanical AGN feedback model.
