Simulating galaxies in the reionization era with FIRE-2: Galaxy scaling relations, stellar mass functions, and luminosity functions

Abstract

We present a suite of cosmological zoom-in simulations at z ≥ 5 from the Feedback In Realistic Environments project, spanning a halo mass range Mhalo ~ 108-1012M⊙ at z = 5. We predict the stellar mass-halo mass relation, stellar mass function, and luminosity function in several bands from z = 5 to 12. The median stellar mass-halo mass relation does not evolve strongly at z = 5-12. The faint-end slope of the luminosity function steepens with increasing redshift, as inherited from the halo mass function at these redshifts. Below z ~ 6, the stellar mass function and ultraviolet (UV) luminosity function slightly flatten below M* ~ 104.5M⊙ (fainter than M1500 ~ -12), owing to the fact that star formation in low-mass haloes is suppressed by the ionizing background by the end of reionization. Such flattening does not appear at higher redshifts. We provide redshift-dependent fitting functions for the SFR-Mhalo, SFR-M*, and broad-band magnitude-stellar mass relations. We derive the star formation rate density and stellar mass density at z = 5-12 and show that the contribution from very faint galaxies becomes more important at z > 8. Furthermore, we find that the decline in the z ~ 6 UV luminosity function brighter than M1500 ~ -20 is largely due to dust attenuation. Approximately 37 per cent (54 per cent) of the UV luminosity from galaxies brighter than M1500 =-13 (-17) is obscured by dust at z ~ 6. Our results broadly agree with current data and can be tested by future observations.