The Characteristic Star Formation Histories of Galaxies at Redshifts z ~ 2-7
Abstract
A large sample of spectroscopically confirmed star-forming galaxies at redshifts 1.4 ≤ z_(spec) ≤ 3.7, with complementary imaging in the near- and mid-IR from the ground and from the Hubble Space Telescope and Spitzer Space Telescope, is used to infer the average star formation histories (SFHs) of typical galaxies from z ∼ 2 to 7. For a subset of 302 galaxies at 1.5 ≤ z_(spec) < 2.6, we perform a detailed comparison of star formation rates (SFRs) determined from spectral energy distribution (SED) modeling (SFRs[SED]) and those calculated from deep Keck UV and Spitzer/MIPS 24μm imaging (SFRs[IR+UV]). Exponentially declining SFHs yield SFRs[SED] that are 5–10 times lower on average than SFRs[IR+UV], indicating that declining SFHs may not be accurate for typical galaxies at z ≳ 2. The SFRs of z ∼ 2–3 galaxies are directly proportional to their stellar masses (M_*), with unity slope—a result that is confirmed with Spitzer/IRAC stacks of 1179 UV-faint (R > 25.5) galaxies—for M_* ≳ 5 × 10^8M_⊙ and SFRs ≳ 2M_⊙ yr^(−1). We interpret this result in the context of several systematic biases that can affect determinations of the SFR–M_* relation. The average specific SFRs at z ∼ 2–3 are remarkably similar within a factor of two to those measured at z ≳ 4, implying that the average SFH is one where SFRs increase with time. A consequence of these rising SFHs is that (1) a substantial fraction of UV-bright z ∼ 2–3 galaxies had faint sub-L* progenitors at z ≳ 4; and (2) gas masses must increase with time from z = 2 to 7, over which time the net cold gas accretion rate—as inferred from the specific SFR and the Kennicutt–Schmidt relation—is ∼2–3 times larger than the SFR. However, if we evolve to higher redshift the SFHs and masses of the halos that are expected to host L* galaxies at z ∼ 2, then we find that ≾10% of the baryons accreted onto typical halos at z ≳ 4 actually contribute to star formation at those epochs. These results highlight the relative inefficiency of star formation even at early cosmic times when galaxies were first assembling.
Additional Information
© 2012 The American Astronomical Society. Received 2012 February 12; accepted 2012 April 27; published 2012 July 2. N.A.R. thanks Rychard Bouwens, Romeel Davé, Claude-André Faucher-Giguère, and Kristian Finlator for useful discussions and comments. We acknowledge the referee for useful suggestions that improved the clarity of the manuscript. We thank the staff of the Keck and Palomar Observatories for their help in obtaining the data presented here. Support for N.A.R. was provided by NASA through Hubble Fellowship Grant HST-HF-01223.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. Additional support has been provided by research funding for the Spitzer Space Telescope Legacy Science Program, provided by NASA through contracts 1224666 and 1287778, issued by the Jet Propulsion Laboratory, California Institute of Technology. N.A.R. also acknowledges the Beatrice Tinsley Visiting Scholar program administered by the Astronomy Department at the University of Texas at Austin, where part of this research was conducted as well as the visitors program at the Institute of Astronomy in Cambridge, UK. C.C.S. has been supported by NSF Grants AST-0606912 and AST-0908805, with additional support from the John D. and Catherine T. MacArthur Foundation and the Peter and Patricia Gruber Foundation. Based, in part, on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and made possible by the generous financial support of the W. M. Keck Foundation.Attached Files
Published - Reddy2012p19053Astrophys_J.pdf
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Additional details
- Eprint ID
- 32991
- Resolver ID
- CaltechAUTHORS:20120807-145459722
- HST-HF-01223.01
- NASA Hubble Fellowship
- 1224666
- NASA
- 1287778
- NASA
- University of Texas at Austin
- AST-0606912
- NSF
- AST-0908805
- NSF
- John D. and Catherine T. MacArthur Foundation
- Peter and Patricia Gruber Foundation
- NAS 5-26555
- NASA
- W. M. Keck Foundation
- Created
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2012-08-07Created from EPrint's datestamp field
- Updated
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2021-11-09Created from EPrint's last_modified field