Regions of highest confidence in the f_cyl-p_ext plane for the fit of the surface density profile at 250, 350, and 500   μm with the model of an isothermal self-gravitating pressurized infinite cylinder (dark grey: 68%, medium grey: 90%, light grey: 99%). The cylinder is assumed to be seen edge-on. The corresponding overpressure p_c/p_ext = (1 − f_cyl)^-2 is labeled on the right axis. The black curves give the column densities of neutral hydrogen through the centre, labelled with log ₁₀N_H(0)    [10²¹   cm^-2] . The grey lines give the FWHM in parsec.