The MOSDEF Survey: The Evolution of the Mass-Metallicity Relation from z = 0 to z ∼ 3.3

We investigate the evolution of galaxy gas-phase metallicity (O/H) over the range z = 0-3.3 using samples of ∼300 galaxies at z ∼ 2.3 and ∼150 galaxies at z ∼ 3.3 from the MOSDEF survey. This analysis crucially utilizes different metallicity calibrations at z ∼ 0 and z > 1 to account for evolving interstellar medium (ISM) conditions. We find significant correlations between O/H and stellar mass (M ∗) at z ∼ 2.3 and z ∼ 3.3. The low-mass power-law slope of the mass-metallicity relation (MZR) is remarkably invariant over z = 0-3.3, such that O/H ∝ M∗0.30 at all redshifts in this range. At fixed M ∗, O/H decreases with increasing redshift as dlog(O/H)/dz = -0.11 ± 0.02. We find no evidence that the fundamental metallicity relation between M ∗, O/H, and star formation rate evolves out to z ∼ 3.3. We employ analytic chemical evolution models to place constraints on the mass and metal loading factors of galactic outflows. The efficiency of metal removal increases toward lower M ∗ at fixed redshift and toward higher redshift at fixed M ∗. These models suggest that the slope of the MZR is primarily set by the scaling of the outflow metal loading factor with M ∗, not by the change in gas fraction as a function of M ∗. The evolution toward lower O/H at fixed M ∗ with increasing redshift is driven by both higher gas fraction (leading to stronger dilution of ISM metals) and higher metal removal efficiency. These results suggest that the processes governing the smooth baryonic growth of galaxies via gas flows and star formation hold in the same form over at least the past 12 Gyr. © 2021. The American Astronomical Society. All rights reserved..