Takata, Tadafumi and Sekiguchi, Kazuhiro and Smail, Ian and Chapman, Scott C. and Geach, J. E. and Swinbank, A. M. and Blain, Andrew and Ivison, R. J. (2006) Rest-Frame Optical Spectroscopic Classifications for Submillimeter Galaxies. Astrophysical Journal, 651 (2). pp. 713-727. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20110211-113035552
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We report the results of a systematic near-IR spectroscopic survey using the Subaru, VLT, and Keck Telescopes of a sample of high-redshift ULIRGs mainly composed of submillimeter-selected galaxies. Our observations span the rest-frame optical range containing nebular emission lines such as Hβ, [O III] λλ4959, 5007, and [O II] λ3727, which are essential for making robust diagnostics of the physical properties. Using the Hα/Hβ emission line ratios, we derive internal extinction estimates for these galaxies similar to those of local ULIRGs: A_V ~ 2.9 ± 0.5. Correcting the Hα estimates of the star formation rate for dust extinction results in rates that are consistent with those estimated from the far-IR luminosity. The majority (>60%) of our sample show spectral features characteristic of AGNs (although this partially reflects an observational bias), with ~65% exhibiting broad Balmer emission lines. A proportion of these sources show relatively low [O III] λ5007/Hβ line ratios, which are similar to those of narrow-line Seyfert 1 galaxies, suggesting low-mass black holes that are rapidly growing. In the subsample of our survey with both [O III] λ5007 and hard X-ray coverage, at least ~60% show an excess of [O III] λ5007 emission, by a factor of 5-10, relative to the hard X-ray luminosity compared to the correlation between these two properties seen in Seyfert galaxies and QSOs locally. From our spectral diagnostics, we propose that the strong [O III] λ5007 emission in these galaxies arises from shocks in dense gaseous regions. Due to sensitivity and resolution limits, our sample is biased to strong-line emitters and hence our results do not yet provide a complete view of the physical properties of the whole high-redshift ULIRG population.
|Additional Information:||© 2006 American Astronomical Society. Received 2006 June 19; accepted 2006 July 24. Based partly on data collected at Subaru Telescope and obtained from the SMOKA science archive at the Astronomy Data Analysis Center, which are operated by the National Astronomical Observatory of Japan. Based partly on the data collected with the ESO VLT-UT1 Antu Telescope [074.B-0107(A)]. Based partly on data obtained at the Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The observatory was made possible by the generous financial support of the W. M. Keck Foundation. We are grateful to Michael Balogh, Bob Nichol, Chris Miller, and Dave Alexander for providing invaluable information and discussions. T. T. and K. S. are also grateful to all staffs of the Subaru Telescope, especially Kentaro Aoki and Takuya Fujiyoshi for support on our Subaru/OHS observation. We also thank the anonymous referee for various comments and suggestions that helped to improve our manuscript. I. R. S. acknowledges support from the Royal Society. J. E. G. acknowledges support from a PPARC postgraduate studentship. A. M. S. acknowledges a PPARC fellowship.|
|Subject Keywords:||galaxies: active; galaxies: evolution; galaxies: high-redshift; submillimeter|
|Official Citation:||Tadafumi Takata et al. 2006 ApJ 651 713 doi: 10.1086/507985|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||11 Feb 2011 22:58|
|Last Modified:||26 Dec 2012 12:55|
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