Relations p vs. I_ν for clump centres (colour images) and for background at 30′ distance (contours, in steps of 0.2 from 0.1 to 0.9 of the peak value). The plots include all clumps at d = 231 pc viewed from the x and y directions (frame a) and a subset with S/N > 10 and T_d< 13 K (frame b). The dashed red line in frame b shows the upper envelope derived in Planck Collaboration Int. XX (2015). The cyan line is the relation estimated for the dense filament G035.39-00.33 (Juvela et al. 2018c) and is drawn for N(H₂) > 10²² cm⁻². The column density scale corresponding to T_d = 15 K.