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

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 ∼ 10^8–10^(12) M⊙ 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* ∼ 10^(4.5) M⊙ (fainter than M_(1500) ∼ −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–M_(halo), 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 M_(1500) ∼ −20 is largely due to dust attenuation. Approximately 37 per cent (54 per cent) of the UV luminosity from galaxies brighter than M_(1500) = −13 (−17) is obscured by dust at z ∼ 6. Our results broadly agree with current data and can be tested by future observations.