  We explore the nature of heavily obscured quasar host galaxies at z~2 using
deep Hubble Space Telescope WFC3/IR imaging of 28 Dust Obscured Galaxies (DOGs)
to investigate the role of major mergers in driving black hole growth. The high
levels of obscuration of the quasars selected for this study act as a natural
coronagraph, blocking the quasar light and allowing a clear view of the
underlying host galaxy. The sample of heavily obscured quasars represents a
significant fraction of the cosmic mass accretion on supermassive black holes
as the quasars have inferred bolometric luminosities around the break of the
quasar luminosity function. We find that only a small fraction (4%, at most
11-25%) of the quasar host galaxies are major mergers. Fits to their surface
brightness profiles indicate that 90% of the host galaxies are either disk
dominated, or have a significant disk. This disk-like host morphology, and the
corresponding weakness of bulges, is evidence against major mergers and
suggests that secular processes are the predominant driver of massive black
hole growth. Finally, we suggest that the co-incidence of mergers and AGN
activity is luminosity dependent, with only the most luminous quasars being
triggered mostly by major mergers.
