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Weighing the black holes in z ≈ 2 submillimeter-emitting galaxies hosting active galactic nuclei

Alexander, D. M. and Brandt, W. N. and Smail, I. and Swinbank, A. M. and Bauer, F. E. and Blain, A. W. and Chapman, S. C. and Coppin, K. E. K. and Ivison, R. J. and Menéndez-Delmestre, K. (2008) Weighing the black holes in z ≈ 2 submillimeter-emitting galaxies hosting active galactic nuclei. Astronomical Journal, 135 (5). pp. 1968-1981. ISSN 0004-6256. doi:10.1088/0004-6256/135/5/1968.

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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 ≈ 10^44 erg s^−1) are log(MBH/Mʘ) ≈ 8.0 and η ≈ 0.2, respectively; by comparison, X-ray-luminous broad-line SMGs (LX ≈ 10^45 erg s^−1) have log(MBH/Mʘ) ≈ 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/Mʘ) ≈ 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 than those found in comparably massive normal galaxies in the local universe, albeit with considerable uncertainty, and ≳10 times smaller than those predicted for z ≈ 2 luminous quasars and radio galaxies. These results imply that the growth of the black hole lags that of the host galaxy in SMGs, in stark contrast with that previously suggested for radio galaxies and luminous quasars at z ≈ 2. On the basis of current host-galaxy mass constraints, we show that SMGs and their descendants cannot lie significantly above the locally defined MBH–MGAL relationship. We argue that the black holes in the z ≈ 0 descendents of SMGs will have log(MBH/Mʘ) ≈ 8.6, indicating that they only need to grow by a factor of ≈6 by the present day. We show that this amount of black-hole growth can be achieved within current estimates for the submillimeter-bright lifetime of SMGs, provided that the black holes can grow at rates close to the Eddington limit.

Item Type:Article
Related URLs:
URLURL TypeDescription 10.1088/0004-6256/135/5/1968DOIArticle
Alexander, D. M.0000-0002-5896-6313
Brandt, W. N.0000-0002-0167-2453
Smail, I.0000-0003-3037-257X
Bauer, F. E.0000-0002-8686-8737
Blain, A. W.0000-0001-7489-5167
Ivison, R. J.0000-0001-5118-1313
Menéndez-Delmestre, K.0000-0003-3153-5123
Additional Information:© 2008. The American Astronomical Society. Received 2007 June 25; accepted 2008 February 29; published 2008 April 11. Print publication: Issue 5 (2008 May). We gratefully acknowledge support from the Royal Society (DMA; IRS), STFC (AMS; KC), NASA LTSA grant NAG5-13035 (WNB), the Chandra Fellowship program (FEB), and the Alfred P. Sloan Foundation and Research Corporation (AWB). We thank M.Volonteri for insightful conversations, C. Maraston for discussing stellar-mass constraints based on her stellar evolution models, R. McLure for providing SDSS quasar data and useful feedback, and the anonymous referee for a thoughtful report.
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)UNSPECIFIED
NASA Chandra FellowshipUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Research CorporationUNSPECIFIED
Subject Keywords:galaxies: active – galaxies: evolution – infrared: galaxies – X-rays: galaxies
Issue or Number:5
Record Number:CaltechAUTHORS:ALEaj08
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11492
Deposited By: Marie Noren
Deposited On:08 Oct 2008 20:33
Last Modified:08 Nov 2021 22:00

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