Leftpanels: average CO (6–5) and CO (7–6) spectra of each ATLASGAL class scaled to the median distance of the distance-limited sub-sample (d = 3.26 kpc). Right panels: same plot, but the average CO spectra were normalised by their peak intensity. The baseline level is indicated by the solid grey line. The black dashed line marks a velocity of 0 km s ⁻¹. The FWZP of the profiles are shown in the upper right side of the panels (in km s ⁻¹ units), together with the integrated intensity (S_int, in K kms⁻¹ units) of theCO profiles shown in the left panels.