Column density at the center of a spherical (black) and cylindrical (grey) isothermal self-gravitating cloud as a function of the overpressure p_c/p_ext, where p_c is the central pressure and p_ext is the external pressure. The dashed lines indicates the asymptotic behavior for high overpressure where . The external pressure is assumed to be consistent with the mean pressure of 2  ×  10⁴   K/cm³ in the ISM of the Milky Way (Boulares & Cox 1990). The grey dotted lines show the values for a critical stable sphere with an overpressure of 14.04. The diamonds mark the values considered in the paper and correspond to A_V =  [1,2,4,8,16]  mag, where the extinction A_V is derived from the column density using the dust-to-gas ratio N_H/E(B − V) = 5.8  ×  10²¹   cm^-2/mag (Bohlin et al. 1978) and the absolute to relative extinction R_V = 3.1 (Fitzpatrick 1999).