Enhanced star formation in $z\sim6$ quasar companions
  Quasars powered by supermassive black holes (MBH, $>10^8~M_{\odot}$) at
$z\sim 6$ are predicted to reside in cosmic over-dense regions. However,
observations so far could not confirm this expectation due to limited
statistics. The picture is further complicated by the possible effects of
quasar outflows (i.e. feedback) that could either suppress or stimulate the
star formation rate (SFR) of companion galaxies, thus modifying the expected
bias. Here we quantify feedback effects on the properties and detectability of
companions by comparing cosmological zoom-in simulations of a quasar in which
feedback is either included or turned-off. With respect to the no-feedback
case, companions (a) directly impacted by the outflow have their SFR increased
by a factor $2-3$, and (b) tend to be more massive. Both effects shift the
[CII]158$\mu$m and UV luminosity functions toward brighter magnitudes. This
leads us to conclude that quasar feedback slightly increases the effective
quasar bias, boosting the number density of observable quasar companions, in
agreement with what has been found around the brightest quasars of recent ALMA
[CII] surveys. Deeper observations performed with JWST and/or ALMA will improve
the statistical significance of this result by detecting a larger number of
fainter quasar companions.
