Scatter plots between the CO isotopologue excitation temperatures. The color scale encodes the dust temperature T_dust. The ellipsesrepresent the interval of confidence for each estimation: Each ellipse is centered on the estimation of the excitation temperature 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. Dashed red lines show the loci of ratios 1/2, 1, 2, and 4.