Correlation between the column densities N(H₂) of two RT models fitted to observations. Column densities N_A and N_B (black dots) correspond to dust models with τ (250 μm)∕τ (J) equal to 1.6 × 10⁻³ and 1.0 × 10⁻³, respectively. For the RT model with column densities N_A, the red points show the column density estimates derived from the synthetic surface brightness maps. The dashed line is the one-to-one relation. All data are at 20′′ resolution.