(u,v)-amplitude plots of the integrated C¹⁸O emission towards the sources in the observed sample. The grey dotted histograms in each panel indicate the expected amplitude in the absence of any source emission. The solid green line in each panel represents the best fitting Gaussian, while the shaded region indicates the 1σ uncertainty region of the fit. The vertical axis of each panel has been scaled to the Gaussian’s peak flux, whose value is printed in the upper right. The grey dashed lines indicate the 15 kλ lower boundary of the fit. Panels where the (u,v)-amplitudes have been plotted in grey indicate objects whose fits have been rejected (see text for details).