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By D. M. Alexander, W. N. Brandt, I. Smail, A. M. Swinbank, F. E. Bauer, A. W. Blain, S. C. Chapman, K. E. K. Coppin, R. J. Ivison and K. Menéndez-delmestre


We place direct observational constraints on the black-hole masses (MBH) of the cosmologically important z ≈ 2 submillimeter-emitting galaxy (SMG; f850µm> ∼ 4 mJy) population, and use measured host-galaxy masses to explore their evolutionary status. We employ the well-established virial black-hole mass estimator to “weigh ” the black holes of a sample of z ≈ 2 SMGs which exhibit broad Hα or Hβ emission. We find that the average black-hole mass and Eddington ratio (η = Lbol/LEdd) of the lower-luminosity broad-line SMGs (LX ≈ 1044 erg s−1) are log(MBH/M⊙) ≈ 8.0 and η ≈ 0.2, respectively; by comparison, X-ray luminous broadline SMGs (LX ≈ 1045 erg s−1) have log(MBH/M⊙) ≈ 8.4 and η ≈ 0.6. The lower-luminosity broad-line SMGs lie in the same location of the LX–LFIR plane as more typical SMGs hosting X-ray obscured active galactic nuclei and may be intrinsically similar systems, but orientated so that the rest-frame optical nucleus is visible. Under this hypothesis, we conclude that SMGs host black holes with log(MBH/M⊙) ≈ 7.8; we find supporting evidence from observations of local ultra-luminous infrared galaxies. Combining these black-hole mass constraints with measured host-galaxy masses, we find that the black holes in SMGs are> ∼ 3 times smaller tha

Year: 2008
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