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

TL;DR

This study re-examines the galaxy star formation main sequence up to redshift 1.3, revealing a consistent turnover at stellar mass around 10^10 solar masses and providing a new parameterization of the relationship.

Contribution

It introduces a new parameterization of the star formation main sequence that captures the turnover at 10^10 solar masses across redshifts up to 1.3.

Findings

Turnover in the main sequence at M* ~ 10^10 M_sun at all redshifts.

SFR scales as (1+z)^4.12, indicating strong evolution with redshift.

Galaxies above the turnover mass have significantly lower sSFR than extrapolated from lower masses.

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 $\mu$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 $SFR \propto M_{*}^{0.88 \pm 0.06}$ below the turnover mass and $SFR \propto M_{*}^{0.27 \pm 0.04}$ above the turnover mass. Galaxies more massive than $M_\ast \gtrsim 10^{10}\ M_{\rm \odot}$ 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.