Line luminosity of the ¹²CO J = 10–9 emission versus their bolometric luminosity for the entire WISH sample of YSOs (same notation as Fig. 6) and for four galaxies in our local universe and two at high redshifts (black diamonds). The solid line represents the linear fit of the galactic ¹²CO J = 10–9 spectra and the dashed line the linear fit including the values of the six galaxies.