ALMA 26 arcmin2 Survey of GOODS-S at One-millimeter (ASAGAO): X-Ray AGN Properties of Millimeter-selected Galaxies

We investigate the X-ray active galactic nucleus (AGN) properties of millimeter galaxies in the Great Observatories Origins Deep Survey South (GOODS-S) field detected with the Atacama Large Millimeter/submillimeter Array (ALMA), by utilizing the Chandra 7-Ms data, the deepest X-ray survey to date. Our millimeter galaxy sample comes from the ASAGAO survey covering 26 arcmin(2) (12 sources at a 1.2. mm flux-density limit of approximate to 0.6 mJy), supplemented by the deeper but narrower 1.3. mm survey of a part of the ASAGAO field by Dunlop et al. Ofthe 25 total millimeter galaxies, 14 have Chandra counterparts. The observed AGN fractions at z = 1.5-3 are found to be 90(-19)(+8)% and 57(-25)(+23)% for the ultra-luminous and luminous infrared galaxies with log L-IR/L-circle dot = 12-12.8 and log L-IR/L-circle dot = 11.5-12, respectively. The majority (similar to 2/3) of the ALMA and/or Herschel detected X-ray AGNs at z = 1.5-3 appear to be star-formation-dominant populations, having L-X/L-IR ratios smaller than the "simultaneous evolution" value expected from the local black-hole-mass-to-stellar-mass (M-BH-M*) relation. On the basis of the L-X and stellar mass relation, we infer that a large fraction of star-forming galaxies at z = 1.5-3 have black hole masses that are smaller than those expected from the local M-BH-M* relation. This contrasts previous reports on luminous AGNs at the same redshifts detected in wider and shallower surveys, which are subject to selection biases against lower luminosity AGNs. Our results are consistent with an evolutionary scenario in which star formation occurs first, and an AGN-dominant phase follows later, in objects that finally evolve into galaxies with classical bulges.