Black Hole growth and AGN obscuration by instability-driven inflows in
  high-redshift disk galaxies fed by cold streams
  Disk galaxies at high redshift have been predicted to maintain high gas
surface densities due to continuous feeding by intense cold streams leading to
violent gravitational instability, transient features and giant clumps.
Gravitational torques between the perturbations drive angular momentum out and
mass in, and the inflow provides the energy for keeping strong turbulence. We
use analytic estimates of the inflow for a self-regulated unstable disk at a
Toomre stability parameter Q~1, and isolated galaxy simulations capable of
resolving the nuclear inflow down to the central parsec. We predict an average
inflow rate ~10 Msun/yr through the disk of a 10^11 Msun galaxy, with
conditions representative of z~2 stream-fed disks. The inflow rate scales with
disk mass and (1+z)^{3/2}. It includes clump migration and inflow of the
smoother component, valid even if clumps disrupt. This inflow grows the bulge,
while only a fraction ~ 10^-3 of it needs to accrete onto a central black hole
(BH), in order to obey the observed BH-bulge relation. A galaxy of 10^11 Msun
at z~2 is expected to host a BH of ~10^8 Msun, accreting on average with
moderate sub-Eddington luminosity L_X ~ 10^42-43 erg/s, accompanied by brighter
episodes when dense clumps coalesce. We note that in rare massive galaxies at
z~6, the same process may feed 10^9 Msun BH at the Eddington rate. High central
gas column densities can severely obscure AGN in high-redshift disks, possibly
hindering their detection in deep X-ray surveys.
