A Highly Consistent Framework for the Evolution of the Star-Forming "Main Sequence" from z~0-6

TL;DR

This study consolidates 25 literature sources to present a consistent, evolving framework for the star-forming galaxy main sequence from redshift 0 to 6, revealing its stable width and a time-dependent slope.

Contribution

It provides a unified, empirical model of the main sequence evolution, including its slope, scatter, and implications for galaxy star formation histories across cosmic time.

Findings

MS width is approximately 0.2 dex and remains constant over time.

The MS slope decreases with cosmic time, modeled as a linear function of universe age.

Delayed-$ au$ models best describe the star formation histories of MS galaxies.

Abstract

Using a compilation of 25 studies from the literature, we investigate the evolution of the star-forming galaxy (SFG) Main Sequence (MS) in stellar mass and star formation rate (SFR) out to $z \sim 6$. After converting all observations to a common set of calibrations, we find a remarkable consensus among MS observations ($\sim 0.1$ dex 1$\sigma$ interpublication scatter). By fitting for time evolution of the MS in bins of constant mass, we deconvolve the observed scatter about the MS within each observed redshift bins. After accounting for observed scatter between different SFR indicators, we find the width of the MS distribution is $\sim 0.2$ dex and remains constant over cosmic time. Our best fits indicate the slope of the MS is likely time-dependent, with our best fit $\log\textrm{SFR}(M_*,t) = \left(0.84 \pm 0.02 - 0.026 \pm 0.003 \times t\right) \log M_* - \left(6.51 \pm 0.24 - 0.11 \pm 0.03 \times t\right)$, with $t$ the age of the Universe in Gyr. We use our fits to create empirical evolutionary tracks in order to constrain MS galaxy star formation histories (SFHs), finding that (1) the most accurate representations of MS SFHs are given by delayed-$\tau$ models, (2) the decline in fractional stellar mass growth for a "typical" MS galaxy today is approximately linear for most of its lifetime, and (3) scatter about the MS can be generated by galaxies evolving along identical evolutionary tracks assuming an initial $1\sigma$ spread in formation times of $\sim 1.4$ Gyr.