Evolution of the infrared luminosity function and its corresponding dust-obscured star formation rate density out to z ∼ 6

We present a new determination of the evolving far-infrared (FIR) galaxy luminosity function (LF) and the resulting inferred evolution of dust-obscured star-formation rate density ( ρ SFR ) out to redshift z ∼ 6. To establish the evolving comoving number density of FIR-bright objects, we made use of AS2UDS, a high-resolution ALMA follow-up study of the JCMT SCUBA-2 Cosmology Legacy Survey (S2CLS) submilliter imaging in the UKIDSS UDS survey field. In order to estimate the contributions of faint and low-mass sources, we implemented a method in which the faint-end of the IR LF is inferred by stacking (in stellar mass and redshift bins) the optical and near-infrared samples of star-forming galaxies into the appropriate FIR Herschel and submillimeter JCMT maps. Using this information we determined the faint-end slope of the FIR LF in two intermediate redshift bins (where it can be robustly established) and then adopted this result at all other redshifts. The evolution of the characteristic luminosity of the galaxy FIR LF, L ★ , is found to increase monotonically with redshift, evolving as L ★ ∝ z 1.38 ± 0.07 , while the characteristic number density, Φ ★ , is well fit by a double power-law function; it is constant at z < 2.24 and declines as z −4.95 ± 0.73 at higher redshifts. We then calculated the evolution of the corresponding dust-obscured star-formation rate density and compared it with the results from a number of recent studies in the literature. Our analysis confirms that dust-obscured star formation activity dominates ρ SFR at cosmic noon but then becomes progressively less important with increasing redshift. While dusty star-forming galaxies are still found out to the highest redshifts explored here, UV-visible star formation dominates at z > 4, and dust-obscured activity contributes less than 25% to the star formation rate density by z ∼ 6.