σ_v/r^{1 / 2} as a function of column density σ for the regions. In order to be consistent with Heyer et al. (2009), σ_v is the 1D velocity dispersion as defined in Eq. (20) and Σ ≡ M/πr² where M is the mass r is the radius. The solid straight line shows the boundary below which the structures are gravitationally bound. It is defined as σ_v/r^{1 / 2} = (πG/ 5)^{1 / 2}Σ^{1 / 2}. The gray crosses come from the catalogue of giant molecular clouds studied in Roman-Duval et al. (2010).