The impact of supernova feedback on metallicity-gradient evolution in cosmological simulations

Tracing the cosmic path of galaxies requires an understanding of their chemical enrichment and merging histories. One of the most important constraints is the internal structure of galaxies, notably the internal distribution of elements. Using our cosmological chemodynamical simulations, including all relevant physical processes and the latest nucleosynthesis yields, we investigate the evolution of radial metallicity gradients of stellar populations and the interstellar medium within each galaxy. This work explores the role of supernova feedback on the metallicity gradients by comparing three feedback models, ejecting energy in thermal, stochastic and mechanical forms. At z = 0, the mechanical feedback model produces the gradient–mass relations of stars and gas both in excellent agreement with observations; gradients are the steepest at intermediate-mass (M * ∼ 10 10 M ⊙) and flatten in massive galaxies, probably by major mergers. For each model, we predict similar gradient–mass relations up to z = 4 and find that the mechanical feedback model gives flatter gradients of both stars and gas for lowermass galaxies (M * < 10 10 M ⊙) possibly due to suppressed star formation and metal ejection by stellar feedback. With all feedback models, most galaxies have negative gas-phase metallicity gradients up to z = 5, suggesting an inside-out growth, which is consistent with other cosmological simulations but not with recent observations at z ∼ 1–2.5. We find a mild redshift evolution of gradients up to z = 4, with a transition at z = 5 where gradients steepen for both stars and gas. These should be investigated with higher-resolution simulations and observations.