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

Baryonic cycling is reflected in the spatial distribution of metallicity within galaxies; however, 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⋆ ranging from 107 to 109.5 M⊙) based on MUSE wide-field spectroscopic observations. We find that the metallicity gradient has a significant negative correlation (Spearman’s rank correlation coefficient r ≃ −0.56) with M⋆, which is in contrast with the flat or even positive correlation observed for higher-mass galaxies. The 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 gaseous velocity field, and effective yield of metals yeff, only the regularity of gaseous velocity field and yeff have residual correlation with metallicity gradient after controlling for M⋆, in the sense that galaxies with an irregular velocity field or lower yeff favor a less negative or more positive metallicity gradient. Particularly, a linear combination of logarithmic stellar mass and yeff significantly improves the correlation with metallicity gradients (r ∼ −0.68) compared to using stellar mass alone. The lack of correlation with environment disproves gas accretion as a relevant factor shaping the metallicity distribution. The correlation with both gaseous velocity field regularity and yeff implies the importance of stellar feedback-driven metal redistribution within the ISM. Our finding suggests that the metal mixing and transport process, including but not limited to feedback-driven outflow, are more important than in situ metal production in shaping the metallicity distribution of dwarf galaxies.