Cosmic evolution of stellar quenching by AGN feedback: clues from the
  Horizon-AGN simulation
  The observed massive end of the galaxy stellar mass function is steeper than
its predicted dark matter halo counterpart in the standard $\Lambda $CDM
paradigm. In this paper, we investigate the impact of active galactic nuclei
(AGN) feedback on star formation in massive galaxies. We isolate the impact of
AGNs by comparing two simulations from the HORIZON suite, which are identical
except that one also includes super massive black holes (SMBH), and related
feedback models. This allows us to cross-identify individual galaxies between
simulations and quantify the effect of AGN feedback on their properties,
including stellar mass and gas outflows. We find that massive galaxies ($ \rm
M_{*} \geq 10^{11} M_\odot $) are quenched by AGN feedback to the extent that
their stellar masses decrease by up to 80% at $z=0$. SMBHs affect their host
halo through a combination of outflows that reduce their baryonic mass,
particularly for galaxies in the mass range $ \rm 10^9 M_\odot \leq M_{*} \leq
10^{11} M_\odot $, and a disruption of central gas inflows, which limits
in-situ star formation. As a result, net gas inflows onto massive galaxies, $
\rm M_{*} \geq 10^{11} M_\odot $, drop by up to 70%. We measure a redshift
evolution in the stellar mass ratio of twin galaxies with and without AGN
feedback, with galaxies of a given stellar mass showing stronger signs of
quenching earlier on. This evolution is driven by a progressive flattening of
the $\rm M_{\rm SMBH}-M_* $ relation with redshift, particularly for galaxies
with $\rm M_{*} \leq 10^{10} M_\odot $. $\rm M_{\rm SMBH}/M_*$ ratios decrease
over time, as falling average gas densities in galaxies curb SMBH growth.
