Friday

We present a new model for the evolution of spatially-resolved gas-phase metallicities in galaxies from first principles. We show that metallicities depend on four ratios that collectively describe the metal equilibration time-scale, production, transport, consumption, and loss. When normalized by metal diffusion, metallicity gradients are governed by the competition between radial advection, metal production, and accretion of metal-poor gas from the cosmic web. The model naturally explains the varying gradients measured in local spirals, local dwarfs, and high-redshift star-forming galaxies. We use the model to study the cosmic evolution of gradients across redshift, showing that the gradient in Milky Way-like galaxies has steepened over time, in good agreement with both observations and simulations. Reproducing the observed mass-metallicity and mass-metallicity gradient relations in the local Universe from the model also shows that galaxies transition from the advection-dominated to the accretion-dominated regime as they increase in mass. The same transition also occurs in galaxies from high to low redshifts, which mirrors the transition from gravity-driven to star formation feedback-driven turbulence. The shape of metallicity-based galaxy scaling relations is governed by the metal enrichment of outflows. Lastly, we show that the model also explains the observed relationship between metallicity gradients and galaxy kinematics at high redshift.