A rumble in the dark: signatures of self-interacting dark matter in
  Super-Massive Black Hole dynamics and galaxy density profiles
  We explore for the first time the effect of self-interacting dark matter
(SIDM) on the dark matter (DM) and baryonic distribution in massive galaxies
formed in hydrodynamical cosmological simulations, including explicit baryonic
physics treatment. A novel implementation of Super-Massive Black Hole (SMBH)
formation and evolution is used, as in Tremmel et al.(2015, 2016), allowing to
explicitly follow SMBH dynamics at the center of galaxies. A high SIDM constant
cross-section is chosen, $\sigma$=10 $\rm cm^2/gr$, to amplify differences from
CDM models. Milky Way-like galaxies form a shallower DM density profile in SIDM
than they do in CDM, with differences already at 20 kpc scales. This
demonstrates that even for the most massive spirals the effect of SIDM
dominates over the adiabatic contraction due to baryons. Strikingly, the
dynamics of SMBHs differs in the SIDM and reference CDM case. SMBHs in massive
spirals have sunk to the centre of their host galaxy in both the SIDM and CDM
run, while in less massive galaxies about 80$\%$ of the SMBH population is
off-centered in the SIDM case, as opposed to the CDM case in which $\sim$90$\%$
of SMBHs have reached their host's centre. SMBHs are found as far as $\sim$9
kpc away from the centre of their host SIDM galaxy. This difference is due to
the increased dynamical friction timescale caused by the lower DM density in
SIDM galaxies compared to CDM, resulting in 'core stalling'. This pilot work
highlights the importance of simulating in a full hydrodynamical context
different DM models combined to SMBH physics to study their influence on galaxy
formation.
