Number distribution of the integrated ¹²CO intensity, W_CO, as a functionof the total H₂ column-density derived from the γ-ray fits for the anticentre and Chamaeleon regions. In each direction is the sum of , , and contributions. The DNM is assumed to be 50% molecular. We use the X_CO factors derived from γ rays to estimate . The grey line is an arbitrary reference corresponding to X_CO = 10²⁰ cm⁻² K⁻¹ km⁻¹ s. The blue and red contours delimit the least and most populated parts of the distribution found in a simulation of the Milky Way by Smith et al. (2014).