Predicted line fluxes for [C II] [C I], and CO emission lines vs. MH_2,total for multi-component models with power-law distributions. The predictions for [C II] and CO match well the observed measurements, as shown in Figs. A.3 and 5. The predictions for [C I] are purely model-based, since no measurement is available. The dashed gray lines show the relations from M20 while the dashed red lines show the linear regressions fitted to the combined posterior distribution for the entire sample. The shades, symbols, and legends are described in Fig. 4. We indicate the equations of linear regressions fitted to the 2D-PDF of the whole sample, and the associated coefficients of determination R².