A negative stellar mass$-$gaseous metallicity gradient relation of dwarf galaxies modulated by stellar feedback

Abstract

Baryonic cycling is reflected in the spatial distribution of metallicity within galaxies, yet gas-phase metallicity distribution and its connection with other properties of dwarf galaxies are largely unexplored. We present the first systematic study of radial gradients of gas-phase metallicities for a sample of 55 normal nearby star-forming dwarf galaxies (stellar mass $M_{\star }$ ranging from $10^7$ to $10^{9.5}{M}_{\odot }$), based on MUSE spectroscopic observations. We find that metallicity gradient shows a significant negative correlation (correlation coefficient $r\approx -0.56$) with $\log M_{\star }$, in contrast to the flat or even positive correlation observed for higher-mass galaxies. This negative correlation is accompanied by a stronger central suppression of metallicity compared to the outskirts in lower-mass galaxies. Among the other explored galaxy properties-including baryonic mass, star formation distribution, galaxy environment, regularity of the gaseous velocity field, and effective yield of metals $y_{\mathrm{eff}}$-only the velocity field regularity and $y_{\mathrm{eff}}$ show residual correlation with the metallicity gradient after controlling for $M_{\star }$, in the sense that galaxies with irregular velocity fields or lower $y_{\mathrm{eff}}$ tend to have less negative or more positive gradients. Particularly, a linear combination of $\log M_{\star }$ and $\log y_{\mathrm{eff}}$ significantly improves the correlation with metallicity gradient ($r\approx -0.68$) compared to $\log M_{\star }$ alone. The lack of correlation with environment disfavors gas accretion as a dominant factor. Our findings imply that metal mixing and transport processes, including but not limited to feedback-driven outflows, are more important than in-situ metal production in shaping the metallicity distribution of dwarf galaxies.

19 pages, 13 figures, accepted for publication in A&A. The most important findings are shown in Figs 3, 12, and 13

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