Feeding compact bulges and supermassive black holes with low
  angular-momentum cosmic gas at high redshift
  We use cosmological hydrodynamical simulations to show that a significant
fraction of the gas in high redshift rare massive halos falls nearly radially
to their very centre on extremely short timescales. This process results in the
formation of very compact bulges with specific angular momentum a factor
5-30$smaller than the average angular momentum of the baryons in the whole
halo. Such low angular momentum originates both from segregation and effective
cancellation when the gas flows to the centre of the halo along well defined
cold filamentary streams. These filaments penetrate deep inside the halo and
connect to the bulge from multiple rapidly changing directions. Structures
falling in along the filaments (satellite galaxies) or formed by gravitational
instabilities triggered by the inflow (star clusters) further reduce the
angular momentum of the gas in the bulge. Finally, the fraction of gas radially
falling to the centre appears to increase with the mass of the halo; we argue
that this is most likely due to an enhanced cancellation of angular momentum in
rarer halos which are fed by more isotropically distributed cold streams. Such
an increasingly efficient funnelling of low-angular momentum gas to the centre
of very massive halos at high redshift may account for the rapid pace at which
the most massive supermassive black holes grow to reach observed masses around
$10^9$M$_\odot$ at an epoch when the Universe is barely 1 Gyr old.
