CO cloud properties. Upper panel: cloud virial mass as a function of the gas mass derived from the CO luminosity. We applied a N(H₂)/I_CO conversion factor that is one third of the Galactic value to the bridge clouds (red triangles). The orange triangles correspond to a Galactic N(H₂)/I_CO conversion factor. Lower panel: cloud velocity dispersion as a function of the product of size and mass surface density. CPROPS clouds (bridge: red triangles; galaxies: blue boxes) are compared to data from Bolatto et al. (2008; green crosses) and Gratier et al. (2012; black pluses). The orange triangles correspond to a Galactic N(H₂)/I_CO conversion factor. The solid line corresponds to Eq. (2).