A Turnover in the Galaxy Main Sequence of Star Formation at M * ~ 1010 M ⊙ for Redshifts z < 1.3
Casey, Caitlin M.; Kartaltepe, Jeyhan S.; Kewley, Lisa J.; Sanders, D. B.; Schawinski, Kevin; Capak, Peter; Scoville, N. Z.; Ilbert, Olivier; Toft, Sune; Hung, Chao-Ling; Lee, Nicholas; Li, Yanxia; Aussel, Hervé; Le Floc'h, Emeric; Sheth, Kartik; Zahid, H. Jabran; Xiao, Quanbao
United States, Denmark, France, Australia, Switzerland, China
Abstract
The relationship between galaxy star formation rates (SFRs) and stellar masses (M *) is reexamined using a mass-selected sample of ~62,000 star-forming galaxies at z <= 1.3 in the COSMOS 2 deg2 field. Using new far-infrared photometry from Herschel-PACS and SPIRE and Spitzer-MIPS 24 μm, along with derived infrared luminosities from the NRK method based on galaxies' locations in the restframe color-color diagram (NUV - r) versus (r - K), we are able to more accurately determine total SFRs for our complete sample. At all redshifts, the relationship between median SFR and M * follows a power law at low stellar masses, and flattens to nearly constant SFR at high stellar masses. We describe a new parameterization that provides the best fit to the main sequence and characterizes the low mass power-law slope, turnover mass, and overall scaling. The turnover in the main sequence occurs at a characteristic mass of about M 0 ~ 1010 M ⊙ at all redshifts. The low mass power-law slope ranges from 0.9-1.3 and the overall scaling rises in SFR as a function of (1 + z)4.12 ± 0.10. A broken power-law fit below and above the turnover mass gives relationships of SFR \propto M*0.88 +/- 0.06 below the turnover mass and SFR \propto M*0.27 +/- 0.04 above the turnover mass. Galaxies more massive than M * >~ 1010 M ⊙ have a much lower average specific star formation rate (sSFR) than would be expected by simply extrapolating the traditional linear fit to the main sequence found for less massive galaxies.