HST WFC3/IR Observations of Active Galactic Nucleus Host Galaxies at
  z~2: Supermassive Black Holes Grow in Disk Galaxies
  We present the rest-frame optical morphologies of active galactic nucleus
(AGN) host galaxies at 1.5<z<3, using near-infrared imaging from the Hubble
Space Telescope Wide Field Camera 3, the first such study of AGN host galaxies
at these redshifts. The AGN are X-ray selected from the Chandra Deep Field
South and have typical luminosities of 1E42 < L_X < 1E44 erg/s. Accreting black
holes in this luminosity and redshift range account for a substantial fraction
of the total space density and black hole mass growth over cosmic time; they
thus represent an important mode of black hole growth in the universe. We find
that the majority (~80%) of the host galaxies of these AGN have low Sersic
indices indicative of disk-dominated light profiles, suggesting that secular
processes govern a significant fraction of the cosmic growth of black holes.
That is, many black holes in the present-day universe grew much of their mass
in disk-dominated galaxies and not in early-type galaxies or major mergers. The
properties of the AGN host galaxies are furthermore indistinguishable from
their parent galaxy population and we find no strong evolution in either
effective radii or morphological mix between z~2 and z~0.05.
