On the Dynamics of Supermassive Black Holes in Gas-Rich, Star-Forming
  Galaxies: the Case for Nuclear Star Cluster Coevolution
  We introduce a new model for the formation and evolution of supermassive
black holes (SMBHs) in the RAMSES code using sink particles, improving over
previous work the treatment of gas accretion and dynamical evolution. This new
model is tested against a suite of high-resolution simulations of an isolated,
gas-rich, cooling halo. We study the effect of various feedback models on the
SMBH growth and its dynamics within the galaxy.
  In runs without any feedback, the SMBH is trapped within a massive bulge and
is therefore able to grow quickly, but only if the seed mass is chosen larger
than the minimum Jeans mass resolved by the simulation. We demonstrate that, in
the absence of supernovae (SN) feedback, the maximum SMBH mass is reached when
Active Galactic Nucleus (AGN) heating balances gas cooling in the nuclear
region.
  When our efficient SN feedback is included, it completely prevents bulge
formation, so that massive gas clumps can perturb the SMBH orbit, and reduce
the accretion rate significantly. To overcome this issue, we propose an
observationally motivated model for the joint evolution of the SMBH and a
parent nuclear star cluster (NSC), which allows the SMBH to remain in the
nuclear region, grow fast and resist external perturbations. In this scenario,
however, SN feedback controls the gas supply and the maximum SMBH mass now
depends on the balance between AGN heating and gravity. We conclude that
SMBH/NSC co-evolution is crucial for the growth of SMBH in high-z galaxies, the
progenitors of massive elliptical today.
