Integrated line flux (calculated at 140 pc) of the HD 1–0 transition as a function of disk mass, representing the high mass end of the left panel of Fig. 2. The horizontal black solid line gives the observation of TW Hya, scaled to a distance of 140 pc, with the black shaded region representing the 1σ uncertainties (Bergin et al. 2013). The observations for DM Tau and GM Aur (McClure et al. 2016) are shown in purple and green, respectively.