Journal
ASTROPHYSICAL JOURNAL
Volume 754, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/754/1/25
Keywords
dust, extinction; galaxies: evolution; galaxies: formation; galaxies: high-redshift; galaxies: star formation
Categories
Funding
- W. M. Keck Foundation
- NASA through Hubble Fellowship [HST-HF-01223.01]
- Space Telescope Science Institute
- NASA [NAS 5-26555, 1224666, 1287778]
- Jet Propulsion Laboratory, California Institute of Technology
- NSF [AST-0606912, AST-0908805]
- STFC [ST/H004912/1, ST/J000647/1, ST/J001538/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/J000647/1, ST/J001538/1, ST/H004912/1, ST/H00243X/1] Funding Source: researchfish
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [0908805] Funding Source: National Science Foundation
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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 similar to 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 24 mu m 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 greater than or similar to 2. The SFRs of z similar to 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-* greater than or similar to 5 x 10(8) M-circle dot and SFRs greater than or similar to 2M(circle dot) 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 similar to 2-3 are remarkably similar within a factor of two to those measured at z greater than or similar to 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 similar to 2-3 galaxies had faint sub-L* progenitors at z similar to 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 similar to 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 similar to 2, then we find that less than or similar to 10% of the baryons accreted onto typical halos at z greater than or similar to 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.
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