Tracing the History of Obscured Star Formation with the SIMBA Cosmological Galaxy Evolution Simulation

Abstract We explore the cosmic evolution of the fraction of dust-obscured star formation predicted by the simba cosmological hydrodynamic simulations featuring an on-the-fly model for dust formation, evolution, and destruction. We find that up to z = 3, our results are broadly consistent with previous observational results of little to no evolution in obscured star formation. However, at z > 3 we find strong evolution at fixed galaxy stellar mass toward greater amounts of obscured star formation, in tension with high-redshift observations. We explain the trend of increasing obscuration at higher redshifts by evolving star-dust geometry, as the dust-to-stellar mass ratios remain relatively constant across cosmic time. We additionally see that at a fixed redshift, more massive galaxies have a higher fraction of their star formation obscured, which is explained by increased dust-to-stellar mass ratios at higher stellar masses. Finally, we estimate the contribution of dust-obscured star formation to the total star formation rate budget and find that the dust-obscured star formation history peaks around z ∼ 2−3, and becomes subdominant at z ≳ 5. The dominance of obscured star formation at redshifts z ≲ 4 is consistent with our results for the evolution of the obscured star formation fraction at fixed stellar mass to higher values at higher redshift because there exist fewer massive, heavily obscured galaxies at high redshift.