R_mol against the normalized radius r_gal/r₂₅. The region below the dotted horizontal line at R_mol = 1 can be viewed as dominated by Σ_HI, and the region above that line by Σ_H2. Left: grey line shows a fit for all the galaxies and it crosses the R_mol = 1 boundary at r_gal ∼ 0.4 r₂₅, which means that the atomic gas on average becomes molecular inside that radius in these eight galaxies. The grey shaded region corresponds to the 3σ confidence interval. Right: colored lines show fits for individual galaxies. We list the corresponding fit parameters in Table 4.