THE CHARACTERISTIC STAR FORMATION HISTORIES OF GALAXIES AT REDSHIFTS z {approx} 2-7
- National Optical Astronomy Observatory, 950 N Cherry Avenue, Tucson, AZ 85719 (United States)
- Institute of Astronomy, Madingley Road, Cambridge CB3 OHA (United Kingdom)
- Department of Astronomy, California Institute of Technology, MS 105-24, Pasadena, CA 91125 (United States)
- Department of Physics and Astronomy, University of California, Los Angeles, 430 Portola Plaza, Los Angeles, CA 90024 (United States)
- Department of Physics, University of Wisconsin, Milwaukee, 1900 E Kenwood Blvd, Milwaukee, WI 53211 (United States)
- Dunlap Institute for Astronomy and Astrophysics, 50 St. George St., Toronto, ON M5S 3H4 (Canada)
A large sample of spectroscopically confirmed star-forming galaxies at redshifts 1.4 {<=} z{sub 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 {approx} 2 to 7. For a subset of 302 galaxies at 1.5 {<=} z{sub 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 {approx}> 2. The SFRs of z {approx} 2-3 galaxies are directly proportional to their stellar masses (M{sub *}), with unity slope-a result that is confirmed with Spitzer/IRAC stacks of 1179 UV-faint (R>25.5) galaxies-for M{sub *} {approx}> 5 Multiplication-Sign 10{sup 8} M{sub Sun} and SFRs {approx}> 2 M{sub Sun} yr{sup -1}. We interpret this result in the context of several systematic biases that can affect determinations of the SFR-M{sub *} relation. The average specific SFRs at z {approx} 2-3 are remarkably similar within a factor of two to those measured at z {approx}> 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 {approx} 2-3 galaxies had faint sub-L* progenitors at z {approx}> 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 {approx}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 {approx} 2, then we find that {approx}< 10% of the baryons accreted onto typical halos at z {approx}> 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.
- OSTI ID:
- 22039317
- Journal Information:
- Astrophysical Journal, Vol. 754, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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