Top panel: non-thermal component of the velocity line width of the C¹⁸O (1−0) transition, vs. the total clump mass, M_clump = M_HiGAL (see text). Stars represent protostellar clumps and the empty circles represent starless clumps. Bottom panel: non-thermal velocity dispersion, from C¹⁸O (1−0), to sound speed ratio, f_turb, vs. the total clump mass, M_clump. The green solid line represents the linear fit to all points (see text); the Spearman rank coefficient is 0.66.