Correlation between the gas and dust mass column densities. Each panel corresponds to a model. The spatial resolution is R4 (54 pc). The colored area is the pixel density. The number density of pixels for each  [Σ_gas,Σ_dust]  values is coded with the same color scale as in Fig. 13. The circles with error bars show the binned trend. The horizontal error bar displays the Σ_gas bin width. The vertical error bar displays the dispersion in Σ_dust within each Σ_gas bin. The Σ_gas bin sizes are chosen so that each bin contains the same number of pixels. The red line is the best fit of Eq. (24) to the binned trend. The vertical lines show the best fit values and . The horizontal line shows the best fit value of of .