Relative fraction of stellar, atomic-gas, and molecular-gas mass surface densities as a function of radius. The solid thick and thin lines show the average Σ_∗/Σ_b and 1σ scatter, respectively. The dashed thick and thin lines (enclosing the light gray area) and the dashed-dotted thick and thin lines (enclosing the dark gray area) show the average Σ_atom/Σ_b and Σ_mol/Σ_b, respectively, again with the thin lines indicating 1σ scatter.