Star Formation at $4 < z < 6$ From the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH)

TL;DR

This study analyzes star-forming galaxies at redshifts 4 to 6, confirming the extension of the stellar mass and star formation rate correlation known as the 'main sequence' to early cosmic times, with implications for galaxy formation models.

Contribution

It provides the first large-scale measurement of the main sequence of star-forming galaxies at $z o6$, revealing continuous star formation and minimal quenching at these early epochs.

Findings

The main sequence extends to $z o6$ with consistent scatter.

Massive galaxies likely form stars near their Eddington limit.

No evidence of significant quenching before $z o6$.

Abstract

Using the first 50% of data collected for the Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) observations on the 1.8 deg$^2$ Cosmological Evolution Survey (COSMOS) we estimate the masses and star formation rates of 3398 $M_*>10^{10}M_\odot $ star-forming galaxies at $4 < z < 6$ with a substantial population up to $M_* \gtrsim 10^{11.5} M_\odot$. We find that the strong correlation between stellar mass and star formation rate seen at lower redshift (the "main sequence" of star-forming galaxies) extends to $z\sim6$. The observed relation and scatter is consistent with a continued increase in star formation rate at fixed mass in line with extrapolations from lower-redshift observations. It is difficult to explain this continued correlation, especially for the most massive systems, unless the most massive galaxies are forming stars near their Eddington-limited rate from their first collapse. Furthermore, we find no evidence for moderate quenching at higher masses, indicating quenching either has not occurred prior to $z \sim 6$ or else occurs rapidly, so that few galaxies are visible in transition between star-forming and quenched.