Blowing cold flows away: the impact of early AGN activity on the
  formation of a brightest cluster galaxy progenitor
  Supermassive black holes (BH) are powerful sources of energy that are already
in place at very early epochs of the Universe (by z=6). Using hydrodynamical
simulations of the formation of a massive M_vir=5 10^11 M_sun halo by z=6 (the
most massive progenitor of a cluster of M_vir=2 10^15 M_sun at z=0), we
evaluate the impact of Active Galactic Nuclei (AGN) on galaxy mass content, BH
self-regulation, and gas distribution inside this massive halo. We find that SN
feedback has a marginal influence on the stellar structure, and no influence on
the mass distribution on large scales. In contrast, AGN feedback alone is able
to significantly alter the stellar-bulge mass content by quenching star
formation when the BH is self-regulating, and by depleting the cold gas
reservoir in the centre of the galaxy. The growth of the BH proceeds first by a
rapid Eddington-limited period fed by direct cold filamentary infall. When the
energy delivered by the AGN is sufficiently large to unbind the cold gas of the
bulge, the accretion of gas onto the BH is maintained both by smooth gas inflow
and clump migration through the galactic disc triggered by merger-induced
torques. The feedback from the AGN has also a severe consequence on the baryon
mass content within the halo, producing large-scale hot superwinds, able to
blow away some of the cold filamentary material from the centre and reduce the
baryon fraction by more than 30 per cent within the halo's virial radius. Thus
in the very young universe, AGN feedback is likely to be a key process, shaping
the properties of the most massive galaxies.
