Left panel: mean stellar densities as function of the velocity dispersions σ_v for the 23 OCs and OCRs in our sample. Symbols are the same as those in Figs. 13 and 14. A normalized 3D velocity dispersion distribution of OCs (red) and OCRs (black) is represented by the hatched histogram. Right panel: mean stellar densities as a function of the limiting radii (R_lim). The dashed and continuous lines are linear fittings to the loci of points defined by the OCRs and OCs, respectively. Clusters were divided into three age bins, as indicated.