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

Using the first 50% of data collected for the Spitzer Large Area Survey with Hyper-Suprime-Cam observations on the 1.8 deg² Cosmological Evolution Survey we estimate the masses and star formation rates of 3398 M _* > 10¹⁰ M _⊙ star-forming galaxies at 4 < z < 6 with a substantial population up to M _* >~ 10^11.5 M _⊙. 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 ~ 6. 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 ~ 6 or else occurs rapidly, so that few galaxies are visible in transition between star-forming and quenched.