Molecular-to-atomic gas mass ratio within r₂₅ as a function of the morphological stage, from T = 1 to T = 10, assuming a constant (Bolatto et al. 2013, filled blue circles) and a metallicity-dependent (Amorín et al. 2016, empty magenta squares) X_CO. As in Fig. 6, the symbols represent the mean values and their uncertainties in bins of ΔT = 1, except for the types T = 8, 9, 10 that are binned together. The (blue) continuum line is the linear fit of the data points assuming a constant X_CO, the (magenta) dashed line assuming a metallicity-dependent X_CO.