A Turnover in the Galaxy Main Sequence of Star Formation at $M_{\ast }\sim 10^{10}{M}_{\odot }$ for Redshifts $z<1.3$

Abstract

The relationship between galaxy star formation rates (SFR) and stellar masses ($M_{\ast }$) is re-examined using a mass-selected sample of $\sim$62,000 star-forming galaxies at $z\le 1.3$ in the COSMOS 2-deg${}^2$ field. Using new far-infrared photometry from $Herschel$-PACS and SPIRE and $Spitzer$-MIPS 24 $\hat{I}¼$m, along with derived infrared luminosities from the NRK method based on galaxies' locations in the restframe color-color diagram $(NUV-r)$ vs. $(r-K)$, we are able to more accurately determine total SFRs for our complete sample. At all redshifts, the relationship between median $SFR$ and $M_{\ast }$ 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 $M_0\sim 10^{10}{M}_{\odot }$ 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 $(1+z{)}^{4.12\pm 0.10}$. A broken power-law fit below and above the turnover mass gives relationships of $SFR\propto M_{\ast }^{0.88\pm 0.06}$ below the turnover mass and $SFR\propto M_{\ast }^{0.27\pm 0.04}$ above the turnover mass. Galaxies more massive than $M_{\ast }\gtrsim 10^{10}{M}_{\odot }$ have on average, a much lower 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.

16 pages, 7 figures. Accepted for publication in ApJ