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

¹ Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei 230026, China
² School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, China
³ Department of Astronomy and Astrophysics, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
⁴ Sub-department of Astrophysics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
⁵ Deep Space Exploration Laboratory/Department of Astronomy, University of Science and Technology of China, Hefei 230026, People’s Republic of China
⁶ Frontiers Science Center for Planetary Exploration and Emerging Technologies, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China
⁷ European Southern Observatory, Alonso de Cordova 3107, Casilla, 19001 Vitacura, Santiago 19, Chile
⁸ School of Astronomy and Space Science, Nanjing University, Nanjing 210093, China
⁹ Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210093, China
¹⁰ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
¹¹ Department of Astronomy, Tsinghua University, Beijing, Beijing 100084, China
¹² Department of Astronomy, Westlake University, Hangzhou, 310030 Zhejiang Province, China
¹³ Department of Astronomy and Institute of Theoretical Physics and Astrophysics, Xiamen University, Xiamen 361005, China
¹⁴ School of Astronomy and Space Science, University of Chinese Academy of Sciences (UCAS), Beijing 100049, People’s Republic of China
¹⁵ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China
¹⁶ Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University Beijing 102206, People’s Republic of China
¹⁷ College of Physics and Electronic Engineering, Qujing Normal University, Qujing, Yunnan 655011, China

^⋆ Corresponding author: hzhang18@ustc.edu.cn

Received: 13 November 2024
Accepted: 22 April 2025

Abstract

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 10^9.5 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 y_eff, only the regularity of gaseous velocity field and y_eff have residual correlation with metallicity gradient after controlling for M_⋆, in the sense that galaxies with an irregular velocity field or lower y_eff favor a less negative or more positive metallicity gradient. Particularly, a linear combination of logarithmic stellar mass and y_eff 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 y_eff 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.