The Influence of Galaxy Surface Brightness on the Mass–metallicity Relation

We study the effect of surface brightness on the mass–metallicity relation using nearby galaxies whose gas content and metallicity profiles are available. Previous studies using fiber spectra indicated that lower surface brightness galaxies have systematically lower metallicities for their stellar mass, but the results were uncertain because of aperture effects. With stellar masses and surface brightnesses measured at Wide-field Infrared Explorer W1 and W2 bands, we re-investigate the surface brightness dependence with spatially resolved metallicity profiles and find similar results. We further demonstrate that the systematical difference cannot be explained by the gas content of galaxies. For two galaxies with similar stellar and gas masses, the one with lower surface brightness tends to have a lower metallicity. Using chemical evolution models, we investigate the inflow and outflow properties of galaxies of different masses and surface brightnesses. We find that, on average, high mass galaxies have lower inflow and outflow rates relative to the star formation rate. On the other hand, galaxies with a lower surface brightness experience stronger inflow than galaxies with a higher surface brightness of a similar mass. The surface brightness effect is more significant for low-mass galaxies. We discuss implications on the different inflow properties between low and high surface brightness galaxies, including star formation efficiency, environment, and mass assembly history.