An analytical model for galaxy metallicity: What do metallicity relations tell us about star formation and outflow?

Understand

We develop a simple analytical model that tracks galactic metallicities governed by star formation and feedback to gain insight from the observed galaxy stellar mass-metallicity relations over a large range of stellar masses and redshifts.

• The model reveals the following implications of star formation and feedback processes in galaxy formation.
• First, the observed metallicity relations provide a stringent upper limit for the averaged outflow mass-loading factors of local galaxies, which is ~20 for M_*~10^9Msun galaxies and monotonically decreases to ~1 for M_*~10^{11}Msun galaxies.
• Second, the inferred upper-limit for the outflow mass-loading factor sensitively depends on whether the outflow is metal-enriched with respect to the ISM metallicity.