The physics of gas phase metallicity gradients in galaxies

We present a new model for the evolution of gas phase metallicity gradients in galaxies from first principles. show that depend on four ratios collectively describe metal equilibration timescale, production, transport, consumption, and loss. Our finds most galaxy are equilibrium at all redshifts. When normalized by diffusion, governed competition between radial advection, accretion metal-poor cosmic web. The naturally explains varying measured local spirals, dwarfs, high-redshift star-forming galaxies. use to study across redshift, showing gradient Milky Way-like has steepened over time, good agreement with both observations simulations. also predict redshift samples constructed using matched stellar masses abundances. shows massive transition advection-dominated accretion-dominated regime high low redshifts, which mirrors gravity-driven star formation feedback-driven turbulence. Lastly, we ultraluminous infrared (major mergers) inverted seen may not be equilibrium. In subsequent papers this series, observed relationship mass gradients, kinematics.