Curve of growth of the CO(3−2) line emission, showing the integrated flux as a function of the radius of the aperture used for spectra extraction. The fluxes were computed through a Gaussian fitting (details in Appendix A.3). Vertical lines correspond to the MRS of the ALMA and ACA data. Error bars include nominal calibration uncertainties (5% for both ALMA and ACA Band 3). Our ALMA data are not reliable for measuring fluxes beyond r > 10″, where aperture dilution effects become severe due to the poor sensitivity to extended and redshifted components.