A Turnover in the Galaxy Main Sequence of Star Formation at M * ~ 1010 M ☉ for Redshifts z < 1.3

The relationship between galaxy star formation rates (SFRs) and stellar masses (M*) is reexamined using a mass-selected sample of similar to 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 mu m, 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 similar to 10(10) M-circle dot 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 proportional to M*(0.88 +/- 0.06) below the turnover mass and SFR proportional to M*(0.27 +/- 0.04) above the turnover mass. Galaxies more massive than M* greater than or similar to 10(10)M(circle dot) 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.