We present the Mufasa suite of cosmological hydrodynamic simulations, which employs the Gizmo meshless finite mass (MFM) code including H 2 -based star formation, nine-element chemical evolution, two-phase kinetic outflows following scalings from the Feedback in Realistic Environments zoom simulations, and evolving halo mass-based quenching. Our fiducial (50h −1 Mpc) 3 volume is evolved to z = 0 with a quarter billion elements. The predicted galaxy stellar mass functions (GSMF) reproduces observations from z = 4 → 0 to 1.2σ in cosmic variance, providing an unprecedented match to this key diagnostic. The cosmic star formation history and stellar mass growth show general agreement with data, with a strong archaeological downsizing trend such that dwarf galaxies form the majority of their stars after z ∼ 1. We run 25h −1 Mpc and 12.5h −1 Mpc volumes to z = 2 with identical feedback prescriptions, the latter resolving all hydrogen-cooling halos, and the three runs display fair resolution convergence. The specific star formation rates broadly agree with data at z = 0, but are underpredicted at z ∼ 2 by a factor of three, re-emphasizing a longstanding puzzle in galaxy evolution models. We compare runs using MFM and two flavours of Smoothed Particle Hydrodynamics, and show that the GSMF is sensitive to hydrodynamics methodology at the ∼ ×2 level, which is sub-dominant to choices for parameterising feedback.

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 12.5h −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 H 2 fractions, H i (21 cm) and CO luminosity functions, and cosmic gas density evolution. There are mild but significant discrepancies, such as too many high-SFR galaxies, overly metal-rich and H i-poor galaxies at M * 10 10 M , and sS-FRs 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 Ω H2 both scale roughly as ∝ (1 + z) 0.7 out to z ∼ 3, comparable to the rise in H i and H 2 fractions. Mufasa galaxies with high SFR at a given M * have lower metallicities and higher H i and H 2 fractions, following observed trends; we make quantitative predictions for how 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.

We examine how HI and metal absorption lines within low-redshift galaxy halos trace the dynamical state of circumgalactic gas, using cosmological hydrodynamic simulations that include a well-vetted heuristic model for galactic outflows. We categorize inflowing, outflowing, and ambient gas based on its history and fate as tracked in our simulation. Following our earlier work showing that the ionisation level of absorbers was a primary factor in determining the physical conditions of absorbing gas, we show here that it is also a governing factor for its dynamical state. Low-ionisation metal absorbers (e.g. Mg ii) tend to arise in gas that will fall onto galaxies within several Gyr, while high-ionisation metal absorbers (e.g. O vi) generally trace material that was deposited by outflows many Gyr ago. Inflowing gas is dominated by enriched material that was previously ejected in an outflow, hence accretion at low redshifts is typically substantially enriched. Recycling wind material is preferentially found closer to galaxies, and is more dominant in lower-mass halos since high-mass halos have more hot gas that is able to support itself against infall. Low-mass halos also tend to re-eject more of their accreted material, owing to our outflow prescription that employs higher mass loading factors for lower-mass galaxies. Typical HI absorbers trace unenriched ambient material that is not participating in the baryon cycle, but stronger HI absorbers arise in cool, enriched inflowing gas. Instantaneous radial velocity measures of absorbers are generally poor at distinguishing between inflowing and outflowing gas, except in the case of very recent outflows. These results suggest that probing halo gas using a range of absorbers can provide detailed information about the amount and physical conditions of material that is participating in the baryon cycle.