Galaxy formation in the Planck cosmology - IV. Mass and environmental
  quenching, conformity and clustering
  We study the quenching of star formation as a function of redshift,
environment and stellar mass in the galaxy formation simulations of Henriques
et al. (2015), which implement an updated version of the Munich semi-analytic
model (L-GALAXIES) on the two Millennium Simulations after scaling to a Planck
cosmology. In this model massive galaxies are quenched by AGN feedback
depending on both black hole and hot gas mass, and hence indirectly on stellar
mass. In addition, satellite galaxies of any mass can be quenched by
ram-pressure or tidal stripping of gas and through the suppression of gaseous
infall. This combination of processes produces quenching efficiencies which
depend on stellar mass, host halo mass, environment density, distance to group
centre and group central galaxy properties in ways which agree qualitatively
with observation. Some discrepancies remain in dense regions and close to group
centres, where quenching still seems too efficient. In addition, although the
mean stellar age of massive galaxies agrees with observation, the assumed AGN
feedback model allows too much ongoing star formation at late times. The fact
that both AGN feedback and environmental effects are stronger in higher density
environments leads to a correlation between the quenching of central and
satellite galaxies which roughly reproduces observed conformity trends inside
haloes.
