a) Total velocity dispersion versus intrinsic mass per unit length (corrected for inclination effects) for the sample of 46 filaments. The symbols and colors, as well as the y-axis of the plot, are the same as in Fig. 6. The horizontal segment at the bottom of the plot shows the typical error bar on the estimated masses per unit length. Specific error bars are shown for NGC 2264C and DR21 since they are larger⁵. The horizontal dashed line shows the value of the thermal sound speed  ~0.2 km s^-1 for T_gas = 10 K. The vertical grey band marks the theoretical position of the effective critical mass per unit length for effective temperatures in the range 10 ≲ T_eff ≲ 20 K (see text). The dotted line running from bottom left to top right corresponds to M_line = M_line,vir/2, which marks the boundary between unbound and bound filaments located on the left and right hand side of the border line, respectively.The blue solid line, , shows the best power-law fit for the bound filaments. The best-fit exponent remains almost unchanged (0.31    ±    0.08) when the fitting is performed after removing DR21 and NGC 2264C from the sample. b) Corrected virial parameter (α_line,vir) versus intrinsic mass per unit length for the same filaments (x-axis is the same as in panel a)). The vertical grey band is the same as in panel a) andseparates subcritical filaments ( ) on the left from supercritical filaments ( ) on the right. The horizontal dashed line (α_line,vir = 2) shows the boundary between gravitationally unbound (α_line,vir > 2) and bound (α_line,vir < 2) filaments, where .The two blue solid lines show the best fits for the subcritical and supercritical filaments, respectively (see text for details).