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A mid-nfrared spectroscopic study of submillimeter galaxies: luminous starbursts at high redshift

Valiante, Elisabetta, Lutz, D., Sturm, E., Genzel, R., Tacconi, L. J., Lehnert, M. D. and Baker, A. J. 2007. A mid-nfrared spectroscopic study of submillimeter galaxies: luminous starbursts at high redshift. Astrophysical Journal 660 (2) , 1060. 10.1086/513306

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We present rest-frame mid-infrared spectroscopy of a sample of 13 submillimeter galaxies, obtained using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. The sample includes exclusively bright objects from blank fields and cluster lens-assisted surveys that have accurate interferometric positions. We find that the majority of spectra are well fitted by a starburst template or by the superposition of PAH emission features and a weak mid-infrared continuum, the latter a tracer of active galactic nuclei (AGNs; including Compton-thick ones). We obtain mid-infrared spectroscopic redshifts for all nine sources detected with IRS. For three of them the redshifts were previously unknown. The median value of the redshift distribution is z ~ 2.8 if we assume that the four IRS nondetections are at high redshift. The median for the IRS detections alone is z ~ 2.7. Placing the IRS nondetections at similar redshift would require rest-frame mid-IR obscuration larger than is seen in local ULIRGs. The rest-frame mid-infrared spectra and mid- to far-infrared spectral energy distributions are consistent with those of local ultraluminous infrared galaxies but scaled up further in luminosity. The mid-infrared spectra support the scenario that submillimeter galaxies are sites of extreme star formation, rather than X-ray-obscured AGNs, and represent a critical phase in the formation of massive galaxies.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Publisher: IOP Science
ISSN: 0004-637X
Last Modified: 04 Jun 2017 06:07

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