Comparison between the N_Htot from W13 and the N_Htot constrained by our X-ray spectral analysis. The equality line is indicated in purple; the 1σ space of the best-fit function for the region of interest (green, black points) and for the rest of the sky (cyan, red points) are also shown. The reason for the systematic difference is given in the main text. The region of interest is within 45° from (l, b)=(281°, −16°) (top) and from (l, b)=(122° , + 8°) (bottom).