Fit of dust-derived N(H₂) as a function of I_CO for data in radial intervals between 0 and 1 kpc (top), 1−2 kpc (middle), and 4−5 kpc (bottom). No cut in intensity has been applied. The color scale indicates the density of points and the thick red histogram shows the N(H₂) data averaged in bins of 0.5 K km s^-1. The thin green line shows an affine fit between N(H₂) and I_CO; the corresponding fit results are printed in green. The thin red line is a linear fit without an offset; the corresponding fit results are printed in red. Blue cross: average value of the plotted data.