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Published January 10, 2012 | Accepted Version + Published
Journal Article Open

The Star Formation Histories of z ~ 2 Dust-obscured Galaxies and Submillimeter-selected Galaxies


The Spitzer Space Telescope has identified a population of ultraluminous infrared galaxies (ULIRGs) at z ~ 2 that may play an important role in the evolution of massive galaxies. We measure the stellar masses (M_*) of two populations of Spitzer-selected ULIRGs that have extremely red R – [24] colors (dust-obscured galaxies, or DOGs) and compare our results with submillimeter-selected galaxies (SMGs). One set of 39 DOGs has a local maximum in their mid-infrared (mid-IR) spectral energy distribution (SED) at rest frame 1.6 μm associated with stellar emission ("bump DOGs"), while the other set of 51 DOGs have power-law mid-IR SEDs that are typical of obscured active galactic nuclei ("power-law DOGs"). We measure M_* by applying Charlot & Bruzual stellar population synthesis models to broadband photometry in the rest-frame ultraviolet, optical, and near-infrared of each of these populations. Assuming a simple stellar population and a Chabrier initial mass function, we find that power-law DOGs and bump DOGs are on average a factor of 2 and 1.5 more massive than SMGs, respectively (median and inter-quartile M_* values for SMGs, bump DOGs, and power-law DOGs are log(M_*/M_☉) = 10.42^(+0.42)_(–0.36), 10.62^(+0.36)_(–0.32), and 10.71^(+0.40)_(–0.34), respectively). More realistic star formation histories drawn from two competing theories for the nature of ULIRGs at z ~ 2 (major merger versus smooth accretion) can increase these mass estimates by up to 0.5 dex. A comparison of our stellar masses with the instantaneous star formation rate (SFR) in these z ~ 2 ULIRGs provides a preliminary indication supporting high SFRs for a given M_*, a situation that arises more naturally in major mergers than in smooth accretion-powered systems.

Additional Information

© 2012 American Astronomical Society. Received 2011 April 19; accepted 2011 November 11; published 2011 December 22. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Spitzer/MIPS guaranteed time observing was used to image the Boötes field at 24 μm and is critical for the selection of DOGs. We acknowledge our referee, Laura Hainline, whose comments have helped greatly to improve the clarity of the paper. We thank the SDWFS team (particularly Daniel Stern and Matt Ashby) for making the IRAC Legacy data products available to us. We are grateful to the expert assistance of the staff of Kitt Peak National Observatory where the Boötes field observations of the NDWFS were obtained. The authors thank NOAO for supporting the NOAO Deep Wide-Field Survey. In particular, we thank Ed Ajhar, Jenna Claver, Alyson Ford, Tod Lauer, Lissa Miller, Glenn Tiede, and Frank Valdes and the rest of the NDWFS survey team, for their assistance with the execution of the NDWFS. We also thank the staff of the W.M.Keck Observatory, where many of the galaxy redshifts were obtained. R.S.B. gratefully acknowledges financial assistance from HST grants GO10890 and GO11195, without which this research would not have been possible. Support for Programs HST-GO10890 and HST-GO11195 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. The research activities of A.D. and B.T.J. are supported by NOAO, which is operated by the Association of Universities for Research in Astronomy (AURA, inc.) under a cooperative agreement with the National Science Foundation. Facilities: Spitzer, Mayall, Keck:I, Keck:II, Gemini: Gillett.

Attached Files

Published - Bussmann2012p16936Astrophys_J.pdf

Accepted Version - 1111.2869.pdf


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