Metallicity gradient as a function of the total baryonic mass. The red circles represent the galaxies measured in this work. The red dashed line and shaded region represent the best-fit linear relation and its 1σ uncertainties. The blue dashed line represents the best-fit linear relation between the residual metallicity gradient (after removing the stellar mass dependence) and the baryonic mass, and the blue shaded region represents 1σ uncertainties of the best-fit relation, with the slope shown in blue. The green horizontal dashed line marks a metallicity gradient of 0.