Massive Quiescent Galaxies at z>3 in The Millennium Simulation Populated
  by A Semi-analytic Galaxy Formation Model
  We take advantage of the statistical power of the large-volume
dark-matter-only Millennium simulation, combined with a sophisticated
semi-analytic galaxy formation model, to explore whether the recently reported
$z=3.7$ quiescent galaxy ZF-COSMOS-20115 (ZF; Glazebrook et al. 2017) can be
accommodated in current galaxy formation models. In our model, a population of
quiescent galaxies (QGs) with stellar masses and star formation rates
comparable to those of ZF naturally emerges at redshifts $z<4$. There are two
and five ZF analogues at the redshift $3.86$ and $3.58$ in the Millennium
simulation volume, respectively. We demonstrate that, while the $z>3.5$ massive
QGs are rare (about 2\% of the galaxies with the similar stellar masses), the
existing AGN feedback model implemented in the semi-analytic galaxy formation
model can successfully explain the formation of the high-redshift QGs as it
does on their lower redshift counterparts.
