Ratio between the product of the millimeter absorption coefficient κ_d(1.2 mm) and the dust-to-gas mass ratio x_d with the alpha parameter α_vir versus x_d. This ratio is linearly related to the ratio between the millimeter dust luminosity and the virial mass. The data represent the median values of the κ_d(1.2   mm)x_d/α_vir ratio for molecular clouds located in three different environments with different dust-to-gas mass ratio, the Gould Belt in the Milky Way, several regions in the SMC, and the N11 region in the LMC. The error bar is the standard deviation of each population. The values for the molecular clouds in the Gould Belt and the SMC were extracted from Bot et al. (2007). The solid line is the Galactic measurement scaled to different x_d values. The shaded area represents the uncertainty on the dust temperature (from 15 to 25 K).