Relation between the mean density and size of the structures (clumps) defined by thresholding at . The dotted line shows the typical density of the interclump medium (i.e. the density of the diffuse component). The dashed line shows the density above which the gravitational energy of the clump becomes higher than the external surface pressure (P_gr = P_ext). The red diamonds show the structures identified from the column density maps by thresholding at . The resolution limit of the column density data is at log R = −1.0. The black solid circle marks the clump B5 in Perseus, and similarly, the red solid circle marks the same clump when using the threshold of .