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

TL;DR

This work tackles how supernova feedback shapes the radial metallicity gradients of stars and gas in galaxies across cosmic time. It uses cosmological chemodynamical simulations with updated nucleosynthesis yields to compare three SN feedback schemes—thermal, stochastic, and mechanical—within identical initial conditions. At z=0, the mechanical feedback model best matches observed gradient–mass relations, predicting the steepest gradients at intermediate masses and flattening toward both lower and higher masses, consistent with merger-driven mixing and suppressed central enrichment. The analysis finds mild gradient evolution from z=0 to z≈4, with a notable transition around z≈5 where gradients become steeper before flattening again, and provides predictions for high-redshift gradients that can be tested with JWST and IFU surveys. Overall, the results underscore the critical role of feedback in redistributing metals and shaping the internal structure of galaxies over cosmic time, while acknowledging limitations from resolution and sub-grid mixing physics.

Abstract

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 acting as fossils in extra-galactic archaeology. Using our cosmological chemodynamical simulations, which include 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 ($M_*\sim10^{10}M_\odot$) and become flatter 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 lower-mass galaxies ($M_*<10^{10}M_\odot$) possibly due to the suppression of 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 $z\sim1$--2.5. We find a mild redshift evolution of gradients up to $z=4$, while there seems to be an evolutionary transition at $z=5$ where the metallicity gradients become steep for gas and stars. These should be investigated with higher-resolution simulations and observations.

Figures (23)

• Figure 1: Stellar (blue) and gas (orange) distribution for the same massive galaxy A ($M_*\sim 10^{11}M_\odot$) with the thermal, stochastic and mechanical feedback models (1st, 2nd and 3rd panels, respectively). The grey solid and dashed circles represent $1R_{\rm e}$ and $2R_{\rm e}$, respectively. Panels (b) and (c) show the stellar and gas-phase metallicity distributions, respectively, along the $x$ axis. The solid blue and orange lines are the median metallicity in each bin of $x$ (see main text for details) for stellar and gas-phase metallicity, respectively. Panels (d) and (e) are the same as panels (b) and (c) but along the $y$ axis.
• Figure 2: Same as Fig. \ref{['map_highMass']} but for an intermediate-mass galaxy B ($M_*\sim 10^{10}M_\odot$).
• Figure 3: (a) V-band luminosity-weighted (solid lines) and mass-weighted (dashed lines) stellar metallicity profiles for Galaxy A at $z=0.7$ for the thermal (blue), stochastic (orange) and mechanical (red) feedback models. We show the profiles with measurable gradients along the total projected radius $\alpha$, the inner gradient $\alpha_{*,\rm in}$ within $R_{\rm e}={4.59}$ kpc, and the outer gradient $\alpha_{*, \rm out}$ between $R_{\rm e}$ and 2$R_{\rm e}$ (vertical dashed grey lines). (b) SFR-weighted (solid lines) and mass-weighted (dashed lines) gas-phase metallicity profiles for Galaxy A at $z=0.7$ with measurable gradients $\alpha_{\rm g, in}$ in 8 kpc (vertical dashed grey lines). The dotted lines show the best linear regression fits.
• Figure 4: Same as Figure \ref{['Z_R_galA']}, but for Galaxy B with $R_{\rm e}={3.74}$ kpc.
• Figure 5: (a) V-band luminosity-weighted stellar metallicity profiles for lower-mass galaxies ($M_*<10^{10} M_\odot$) with measurable gradients at $z=0.7$ in our simulations. The solid lines are the median for the thermal (blue), stochastic (orange), and mechanical (red) feedback models. The shaded areas are $1 \sigma$ scatter. The dotted lines are the best linear fit of the medians for a single slope $\alpha_{*}$, the inner gradient $\alpha_{*,\rm in}$ within $1R_{\rm e}$, and the outer gradient $\alpha_{*,\rm out}$ between $1R_{\rm e}$ and $2R_{\rm e}$. (b) The same as (a), but for SFR-weighted gas-phase oxygen abundance profiles. The medians are fitted with a single slope (dotted line), such that the gradients $\alpha_{\rm g,in}$ are measured within $r < 8$ kpc.