Abstract
The growth of a supermassive black hole (BH) is determined by how much gas
the host galaxy is able to feed it, which in turn is controlled by the cosmic
environment, through galaxy mergers and accretion of cosmic flows that time how
galaxies obtain their gas, but also by internal processes in the galaxy, such
as star formation and feedback from stars and the BH itself. In this paper, we
study the growth of a 10^12 Msun halo at z=2, which is the progenitor of an
archetypical group of galaxies at z=0, and of its central BH by means of a
high-resolution zoomed cosmological simulation, the Seth simulation. We study
the evolution of the BH driven by the accretion of cold gas in the galaxy, and
explore the efficiency of the feedback from supernovae (SNe). For a relatively
inefficient energy input from SNe, the BH grows at the Eddington rate from
early times, and reaches self-regulation once it is massive enough. We find
that at early cosmic times z>3.5, efficient feedback from SNe forbids the
formation of a settled disc as well as the accumulation of dense cold gas in
the vicinity of the BH and starves the central compact object. As the galaxy
and its halo accumulate mass, they become able to confine the nuclear inflows
provided by major mergers and the BH grows at a sustained near-to-Eddington
accretion rate. We argue that this mechanism should be ubiquitous amongst
low-mass galaxies, corresponding to galaxies with a stellar mass below <10^9
Msun in our simulations.
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