Panels a) and b) are similar to Figs. 2a and b, but for an example of a thermally subcritical filament in the IC 5146 molecular cloud (d ~ 460 pc). The mean line mass of the filament is ⟨M_line⟩ ~ 3M_⊙/pc ≪M_line,crit, as shown by the dotted horizontal line in panel (b). The median relative amplitude of the line-mass fluctuations is , within the linear perturbation regime. Panel c) is similar to Fig. 4 but for the IC 5146 filament. The power-law fits to the power spectra P_obs(s) and P_true(s) have logarithmic slopes −1.8 ± 0.2 and −1.2 ± 0.4, respectively. Considering only angular frequencies up to = 1.5 arcmin^-1, the best power-law fit to P_true(s) has a slope α_true = −1.1 ± 0.3. (This figure is available in color in electronic form.)