The host galaxies of z=7 quasars: predictions from the BlueTides
  simulation
  We examine the properties of the host galaxies of $z=7$ quasars using the
large volume, cosmological hydrodynamical simulation BlueTides. We find that
the 10 most massive black holes and the 191 quasars in the simulation (with
$M_{\textrm{UV,AGN}}<M_{\textrm{UV,host}}$) are hosted by massive galaxies with
stellar masses $\log(M_\ast/M_\odot)=10.8\pm0.2$, and $10.2\pm0.4$, which have
large star formation rates, of $513\substack{+1225 \\ -351}M_\odot/\rm{yr}$ and
$191\substack{+288 \\ -120}M_\odot/\rm{yr}$, respectively. The hosts of the
most massive black holes and quasars in BlueTides are generally
bulge-dominated, with bulge-to-total mass ratio $B/T\simeq0.85\pm0.1$, however
their morphologies are not biased relative to the overall $z=7$ galaxy sample.
We find that the hosts of the most massive black holes and quasars are
significantly more compact, with half-mass radii $R_{0.5}=0.41\substack{+0.18
\\ -0.14}$ kpc and $0.40\substack{+0.11 \\ -0.09}$ kpc respectively; galaxies
with similar masses and luminosities have a wider range of sizes with a larger
median value, $R_{0.5}=0.71\substack{+0.28 \\ -0.25}$ kpc. We make mock James
Webb Space Telescope (JWST) images of these quasars and their host galaxies. We
find that distinguishing the host from the quasar emission will be possible but
still challenging with JWST, due to the small sizes of quasar hosts. We find
that quasar samples are biased tracers of the intrinsic black hole--stellar
mass relation, following a relation that is 0.2 dex higher than that of the
full galaxy sample. Finally, we find that the most massive black holes and
quasars are more likely to be found in denser environments than the typical
$M_{\textrm{BH}}>10^{6.5}M_\odot$ black hole, indicating that minor mergers
play at least some role in growing black holes in the early Universe.
