Mufasa: Galaxy star formation, gas, and metal properties across cosmic time

Abstract

We examine galaxy star formation rates (SFRs), metallicities and gas contents predicted by the Mufasa cosmological hydrodynamic simulations, which employ meshless hydrodynamics and novel feedback prescriptions that yield a good match to observed galaxy stellar mass assembly. We combine 50, 25 and 12.5 h^(−1) Mpc boxes with a quarter billion particles each to show that Mufasa broadly reproduces a wide range of relevant observations, including SFR and specific SFR functions, the mass–metallicity relation, H i and H2 fractions, H i (21 cm) and CO luminosity functions, and cosmic gas density evolution. There are mild but significant discrepancies, such as perhaps too many high-SFR galaxies, overly metal-rich and H i-poor galaxies at M^* ≳ 2 × 10^(10) M_⊙, and specific star formation rates that are too low at z ∼ 1–2. The H i mass function increases by ×2 out to z ∼ 1, then steepens to higher redshifts, while the CO luminosity function computed using the Narayanan et al. conversion factor shows a rapid increase of CO-bright galaxies out to z ∼ 2 in accord with data. Ω_(HI) and ΩH2 both scale roughly as ∝(1 + z)^(0.7) out to z ∼ 3, comparable to the rise in H i and H2 fractions. Mufasa galaxies with high SFR at a given M* have lower metallicities and higher H i and H2 fractions, following observed trends; we make quantitative predictions for how the fluctuations in the baryon cycle drive correlated scatter around galaxy scaling relations. Most of these trends are well converged with numerical resolution. These successes highlight Mufasa as a viable platform to study many facets of cosmological galaxy evolution.

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