Host galaxies of high-redshift quasars: supermassive black hole growth
  and feedback
  The properties of quasar-host galaxies might be determined by the growth and
feedback of their supermassive (SMBH, $10^{8-10}$ M$_{\odot}$) black holes. We
investigate such connection with a suite of cosmological simulations of massive
(halo mass $\approx 10^{12}$ M$_{\odot}$) galaxies at $z\simeq 6$ which include
a detailed sub-grid multiphase gas and accretion model. BH seeds of initial
mass $10^5$ M$_{\odot}$ grow mostly by gas accretion, and become SMBH by $z=6$
setting on the observed $M_{\rm BH} - M_{\star}$ relation without the need for
a boost factor. Although quasar feedback crucially controls the SMBH growth,
its impact on the properties of the host galaxy at $z=6$ is negligible. In our
model, quasar activity can both quench (via gas heating) or enhance (by ISM
over-pressurization) star formation. However, we find that the star formation
history is insensitive to such modulation as it is largely dominated, at least
at $z>6$, by cold gas accretion from the environment that cannot be hindered by
the quasar energy deposition. Although quasar-driven outflows can achieve
velocities $> 1000~\rm km~s^{-1}$, only $\approx 4$% of the outflowing gas mass
can actually escape from the host galaxy. These findings are only loosely
constrained by available data, but can guide observational campaigns searching
for signatures of quasar feedback in early galaxies.
