Relation between optical radius R₂₅ and stellar mass M_sp. Panel a: R₂₅ as a function of M_sp for individual galaxies with R distribution (blue circles) and B distribution (red squares) of the gas velocity dispersion. Panel b: median values of R₂₅ for galaxies in bins of 0.3 dex in M_sp for galaxies with R distribution, shown with blue circles. The solid line is the linear best fit to those data. Red squares denote the binned median values for galaxies with B distribution. The dashed line is the linear best fit to those data.