Strength in numbers: Red Galaxies Bolster the cosmic star formation rate density at <i>z</i> ≳ 3

ABSTRACT A comprehensive account of the cosmic star-formation history demands an accurate census of dust-enshrouded star formation over cosmic time. We provide strong new constraints from a large sample of 777 red galaxies, selected based on their dust-reddened rest-frame UV-optical emission. This sample spans $1 \lt z \lt 8$ and is selected from PRIMER James Webb Space Telescope (JWST) NIRCam and Hubble Space Telescope (HST) COSMOS optical data. The SEDs indicate that these galaxies are star-forming, with median $\mathrm{SFR \sim 40\,{\rm M}_{\odot }\,yr^{-1}}$ and stellar mass $\log (M_{*}/{\rm M}_{\odot }) = 10.3^{+0.6}_{-0.8}$; each exceeds the corresponding medians of the full JWST-detected population by over two dex. Our sample shows that red galaxies dominate the high-mass end, comprising 72 per cent of galaxies with $\log (M/{\rm M}_{\odot }) \gt 10$ at $z = 3.3$, and rising to 91 per cent by $z \sim 7$. Crucially, the number density of massive red star-forming galaxies at $z \sim 6$ is sufficient to explain the abundance of quiescent galaxies at $z \gt 3$, consistent with quenching within a $\mathrm{{\sim} 1\,Gyr}$ interval from $z \sim 6$ to $z \sim 3$. This abundance yields a major contribution to the cosmic star-formation rate density: at $z \sim 4$, red galaxies provide $\mathrm{\rho _{SFR} = 3.9^{+0.6}_{-0.5} \times 10^{-2} {\rm M}_{\odot } yr^{-1}Mpc^{-3}}$, and at $z \sim 5$ they supply nearly 40 per cent of the total $\rho _{\mathrm{ SFR}}$. This contribution exceeds that of bright sub(mm)-selected dusty star-forming galaxies by more than an order of magnitude. Future, deeper, and wider ALMA surveys will further strengthen and extend these results in quantifying the role of dust-obscured activity in $\rho _{\mathrm{SFR}}$ at high redshifts.