Mass as a function of peak column density for synthetic sources (panel a) and for observed clumps (panel b). A simple regression gives the relation with β = 0.37 in panel a over a [0.6 − 12 × 10²¹ cm⁻²] range, β = 0.34 in panel b over a [0.5 − 200 × 10²¹ cm⁻²]. The similarity in the fitted parameters confirms that the synthetic sources correctly represent the observed clumps.