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Mid-infrared spectral diagnosis of submillimeter galaxies

Pope, Alexandra and Chary, Ranga-Ram and Alexander, David M. and Armus, Lee and Dickinson, Mark and Elbaz, David and Frayer, David T. and Scott, Douglas and Teplitz, Harry (2008) Mid-infrared spectral diagnosis of submillimeter galaxies. Astrophysical Journal, 675 (2). pp. 1171-1193. ISSN 0004-637X. doi:10.1086/527030.

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We present deep mid-IR spectroscopy with Spitzer of 13 SMGs in the GOODS-N field.We find strong PAH emission in all of our targets, which allows us to measure mid-IR spectroscopic redshifts and place constraints on the contribution from star formation and AGN activity to the mid-IR emission. In the high-S/N composite spectrum, we find that the hot dust continuum from an AGN contributes at most 30% of the mid-IR luminosity. Individually, only 2/13 SMGs have continuum emission dominating the mid-IR luminosity; one of these SMGs, C1, remains undetected in the deep X-ray images but shows a steeply rising continuum in the mid-IR indicative of a Compton-thick AGN. We find that the mid-IR properties of SMGs are distinct from those of 24 μm–selected ULIRGs at z~2; the former are predominantly dominated by star formation, while the latter are a more heterogeneous sample with many showing significant AGN activity.We fit the IRS spectrum and the mid-IR to radio photometry of SMGs with template SEDs to determine the best estimate of the total IR luminosity from star formation. While many SMGs contain an AGN as evinced by their X-ray properties, our multiwavelength analysis shows that the total IR luminosity, L_(IR), in SMGs is dominated by star formation.We find that high-redshift SMGs lie on the relation between L_(IR) and L_(PAH,6.2) (or L_(PAH,7.7) or L_(PAH,11.3))that has been established for local starburst galaxies. This suggests that PAH luminosity can be used as a proxy for the SFR in SMGs. SMGs are consistent with being a short-lived cool phase in a massive merger where the AGN does not appear to have become strong enough to heat the dust and dominate the mid- or far-IR emission.

Item Type:Article
Related URLs:
URLURL TypeDescription
Pope, Alexandra0000-0001-8592-2706
Chary, Ranga-Ram0000-0001-7583-0621
Alexander, David M.0000-0002-5896-6313
Armus, Lee0000-0003-3498-2973
Dickinson, Mark0000-0001-5414-5131
Elbaz, David0000-0002-7631-647X
Frayer, David T.0000-0003-1924-1122
Scott, Douglas0000-0002-6878-9840
Teplitz, Harry0000-0002-7064-5424
Additional Information:© 2008 American Astronomical Society. Received 2007 August 22, accepted for publication 2007 November 19. We are grateful to the referee for helpful suggestions which improved this paper. We thank Anna Sajina for helpful discussions and for providing composite IRS spectra of their highredshift Spitzer 24 μm–selected ULIRGs.We are very grateful to Bernhard Brandl for providing the IRS spectra of local starburst galaxies and Benjamin Magnelli for providing information from the completeness simulations of the 70 μm images. Support for this work was provided by NASA through the Spitzer Space Telescope Fellowship Program, through a contract issued by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This work was supported by the Natural Sciences and Engineering Research Council of Canada and the Canadian Space Agency. D. M. A. acknowledges the Royal Society for support. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. The IRS was a collaborative venture between Cornell University and Ball Aerospace Corporation funded by NASA through the Jet Propulsion Laboratory and Ames Research Center.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Canadian Space Agency (CSA)UNSPECIFIED
Subject Keywords:galaxies: active; galaxies: evolution; galaxies: starburst; infrared: galaxies; submillimeter; techniques: spectroscopic
Issue or Number:2
Record Number:CaltechAUTHORS:POPapj08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13681
Deposited By: Marie Noren
Deposited On:07 Jul 2009 23:12
Last Modified:08 Nov 2021 22:39

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