Black Hole growth and AGN obscuration by instability-driven inflows in high-redshift disk galaxies fed by cold streams
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Disk galaxies at high redshift maintain high gas surface densities, due to continuous feeding by intense cold streams. This leads to a violent gravitational instability involving transient features and giant clumps. The instability is self-regulated at a Toomre stability parameter Q~1. Torques between the perturbations drive angular momentum out and mass in. The inflow down the potential gradient provides the energy for keeping strong turbulence at the Q~1 level while compensating for dissipative losses. Analytic estimates and simulations with parsec-scale resolution predict, for a gas-rich disk galaxy of 10^11 Msun at z=2, an average inflow rate ~10 Msun/yr into the central kpc. The inflow rate scales with disk mass and (1+z)^{3/2}. This inflow is responsible for the growth of a bulge, while a fraction ~10^{-3}*(1+z) of it needs to accrete onto a central black hole obeying the observed scaling relations. A galaxy of 10^11 Msun z~2 hosts a black hole of ~10^8 Msun, accreting on average in sub-Eddington mode with moderate luminosity L_X~10^{42-43} erg/s, but possibly accompanied by bright Eddington-limited episodes. In early-forming massive systems at z~6, the same process may feed 10^9 Msun black holes from seeds of <10^5Msun at z~10. The inflow also generates high gas column densities that can severely obscure AGN in high-redshift disks.
