(u,v)-amplitude plots of the integrated C¹⁸O emission towards the sources in the JVWB15 sample. The solid green line in each panel is 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 peak flux of the Gaussian fit, whose value is printed in the upper right. The grey dashed lines indicates the 15 kλ lower boundary of the fit.