Panel a: ratio of the disc scale length to the optical radius h_d/R₂₅ as a function of the value of the rotation velocity V_rot. The grey points represent the data for individual MaNGA galaxies from our sample, and the dark points indicate the binned mean values (omitting objects with h_d/R₂₅ >  0.7). The dotted line is the mean h_d/R₂₅ value. Panel b: same as panel a but for the ratio of the effective radius of the galaxy to the optical radius R_e, g/R₂₅.