Impact of AGN feedback on galaxies and their multiphase ISM across
  cosmic time
  We present simulations of galaxy formation, based on the GADGET-3 code, in
which a sub-resolution model for star formation and stellar feedback is
interfaced with a new model for AGN feedback. Our sub-resolution model
describes a multiphase ISM, accounting for hot and cold gas within the same
resolution element: we exploit this feature to investigate the impact of
coupling AGN feedback energy to the different phases of the ISM over cosmic
time. Our fiducial model considers that AGN feedback energy coupling is driven
by the covering factors of the hot and cold phases. We perform a suite of
cosmological hydrodynamical simulations of disc galaxies ($M_{\rm halo, \, DM}
\simeq 2 \cdot 10^{12}$ M$_{\odot}$, at $z=0$), to investigate: $(i)$ the
effect of different ways of coupling AGN feedback energy to the multiphase ISM;
$(ii)$ the impact of different prescriptions for gas accretion (i.e. only cold
gas, both cold and hot gas, with the additional possibility of limiting gas
accretion from cold gas with high angular momentum); $(iii)$ how different
models of gas accretion and coupling of AGN feedback energy affect the
coevolution of supermassive BHs and their host galaxy. We find that at least a
share of the AGN feedback energy has to couple with the diffuse gas, in order
to avoid an excessive growth of the BH mass. When the BH only accretes cold
gas, it experiences a growth that is faster than in the case in which both cold
and hot gas are accreted. If the accretion of cold gas with high angular
momentum is reduced, the BH mass growth is delayed, the BH mass at $z=0$ is
reduced by up to an order of magnitude, and the BH is prevented from accreting
below $z \lesssim 2$, when the galaxy disc forms.
