Zoom of Fig. 4 top: medians of the ¹³CO (3–2) simulated line luminosities for different mass bins, presented with red dots in the region where the luminosity dependence on mass is linear (see Eq. (3)). The red line shows the fit function of the line luminosity as a function of disk mass. The ¹³CO-only detections are shown with gray dashed lines. The pink band shows the maximum and minimum simulated line luminosities.