Physical properties of all structures identified in the simulation Z18 at time 10.04 Myr. Top-left panel: mass versus radius, top-right panel: mean density versus mass. Bottom-left panel: α_vir parameter (as stated by Eq. (8)) for all structures while bottom-right panel: α_vir only for the structures with a mean density larger than 10⁵ cm⁻³. The latter confirms that most structures with a mean density larger than 10⁵ cm⁻³ are collapsed objects since α_vir ≃ 1 (with little dispersion).