The Star Formation Rate Function for Redshift z ~ 4-7 Galaxies: Evidence for a Uniform Buildup of Star-forming Galaxies during the First 3 Gyr of Cosmic Time
Abstract
We combine recent estimates of dust extinction at z ~ 4-7 with UV luminosity function (LF) determinations to derive star formation rate (SFR) functions at z ~ 4-7. SFR functions provide a more physical description of galaxy buildup at high redshift and allow for direct comparisons to SFRs at lower redshifts determined by a variety of techniques. Our SFR functions are derived from well-established z ~ 4-7 UV LFs, UV-continuum slope trends with redshift and luminosity, and infrared excess (IRX)-β relations. They are well described by Schechter relations. We extend the comparison baseline for SFR functions to z ~ 2 by considering recent determinations of the Hα and mid-IR LFs. The low-end slopes of the SFR functions are flatter than for the UV LFs, Δα ~ +0.13, and show no clear evolution with cosmic time (z ~ 0-7). In addition, we find that the characteristic value SFR* from the Schechter fit to the SFR function exhibits consistent, and substantial, linear growth as a function of redshift from ~5 M ⊙ yr-1 at z ~ 8, 650 Myr after the big bang, to ~100 M ⊙ yr-1 at z ~ 2, ~2.5 Gyr later. Recent results at z ~ 10, close to the onset of galaxy formation, are consistent with this trend. The uniformity of this evolution is even greater than seen in the UV LF over the redshift range z ~ 2-8, providing validation for our dust corrections. These results provide strong evidence that galaxies build up uniformly over the first 3 Gyr of cosmic time.
- Publication:
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The Astrophysical Journal
- Pub Date:
- September 2012
- DOI:
- 10.1088/0004-637X/756/1/14
- arXiv:
- arXiv:1204.3626
- Bibcode:
- 2012ApJ...756...14S
- Keywords:
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- galaxies: evolution;
- galaxies: high-redshift;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- Added an appendix, 1 figure and 3 tables: 9 pages, 5 figures, 4 tables, ApJ, in press