A TURNOVER IN THE GALAXY MAIN SEQUENCE OF STAR FORMATION ATM*∼ 1010M☉FOR REDSHIFTSz< 1.3
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 deg 2 field. Using new far-infrared photometry from Herschel-PACS and SPIRE and Spitzer-MIPS 24 m, along with derived infrared luminosities from the NRK method based on galaxies' locations in the restframe color-color diagram (NUVr) 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 10 10 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) 4.120.10 . A broken power-law fit below and above the turnover mass gives relationships of SFR M 0.880.06 * below the turnover mass and SFR M 0.270.04 * above the turnover mass. Galaxies more massive than M * 10 10 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.