Scatter plots between CO isotopologue column densities. The color scale encodes the ratio of the excitation temperatures of the considered species in each panel. The ellipses represent the interval of confidence for each estimation: Each ellipseis centered on the estimation of the column density for one pixel and its horizontal and vertical sizes are equal to the associated CRBs. Dashed ellipses correspond to pixels with two components. Inaccurate estimations are filtered out. The dashed red lines show the loci of ratios 5, 20, and 60.