Scatter plots of the H₂ column density derived from the extinction map against the C¹⁸O (left) and ¹³CO (right) integrated intensity ( K km s^-1) for each pixel in the map. The purple dashed-lines represent the linear fit of the data points, with an upper limit constraint on the column density for the case of ¹³CO. Overlaid on the scatter plots are the predictions of RADEX models at different gas temperatures (on the left: 7.4 K in green and 9.4 K in blue crosses; on the right: 6.6 K in yellow, 9.0 K in green and 11.4 K in blue triangles). For the C¹⁸O (left) the green and blue dashed lines represent the linear approximations to the respective colour-coded RADEX model.