Left: distribution of the sources of the sample in the plane N(H₂) − T_dust. Middle: distribution of the sources of the sample in the plane L − M_SED). Gray tracks are the evolutionary tracks from Molinari et al. (2008), while orange dashed lines indicate L∕M = 1, 10, and 100 L_⊙∕M_⊙. Right: plot of the evolutionary tracers L∕M as a function of T_dust and power-law relation best fit to the data given in orange. The legend for the classification color-code is given in the right panel. Sources that have not been classified yet are plotted in black.