Internal Structure, Not Environment, Shapes Metallicity Gradients in Low-Mass Galaxies from MaNGA

Abstract

Dwarf and low-mass galaxies are highly sensitive to stellar feedback and gas flows, yet their spatially resolved gas-phase metallicity remains poorly characterised. We measure radial gas-phase metallicity gradients for 382 star-forming low-mass galaxies from MaNGA DR17, spanning $7.2\le \log (M_{\star }/M_{\odot })\le 9.1$ and $z\le 0.05$. Spectra are stacked in elliptical radial bins and metallicity is derived from the N2 index. After removing the primary dependence on local stellar mass surface density, we define a residual metallicity $\Delta Z$ to isolate secondary dependencies. Gradients are flat on average (median slope $-0.007$\,dex\,$R_e^{-1}$). The residual gradients correlate most strongly with light concentration ($r=0.304$, $r^2=0.092$, $p<0.001$) and gas velocity dispersion ($r=0.204$, $p<0.001$), though both account for at most 9 per cent of the variance. Large-scale environment shows no significant correlation. The concentration result is robust to measurement uncertainties and persists with a stricter resolution cut, suggesting internal structural properties shape the radial metal distribution in low-mass galaxies.

19 pages, 15 figures, 2 tables. Full data table available as online supplementary material