Institute for Advanced Study Informal Astrophysics Seminar

The gas-phase oxygen abundances of star-forming galaxies are tightly correlated with the galaxies' stellar masses such that more massive galaxies are more oxygen-rich. Because oxygen is produced on relatively short timescales (~10 Myr), this so-called mass-metallicity relation is a sequence of oxygen depletion: low-mass galaxies are metal-depleted relative to the true nucleosynthetic yield rather than massive galaxies being preferentially enriched. Preferential metal-depletion can be caused by either diluting the gas (e.g., via higher accretion rates of pristine gas or by lower star-formation efficiencies) or by preferentially removing metals from low-mass galaxies via galaxy winds. I will use simple analytic arguments to show how the observed mass-metallicity relation implies the required balance between gas dilution and gas outflow. In order to reproduce the mass-metallicity relation in cosmological smoothed particle hydrodynamic (SPH) simulations, star formation feedback is required. The resolution of such simulations, however, demands that this feedback is not directly modeled; I will discuss how I am examining and clarifying the issues surrounding different SPH galaxy wind implementations.