Free-fall timescale to rotational period ratio, t_ff/t_rot, versus gas mass, M_gas, of known rotating disks or toroids. Adapted from Fig. 12 of Beltrán et al. (2011a). The red star corresponds to core A in G35.03. Blue filled dots connected by a dotted line correspond to cores A and B in G35.20–0.74N, which occupy two different positions in the diagram depending on the value of the mass adopted (Sánchez-Monge et al. 2014). The parameters of the HMC G29.96−0.02 have been recalculated for a more correct distance of 6.2 kpc (Russeil et al. 2011) instead of 3.5 kpc, which was the one used by Beltrán et al. (2011a). Black dotted lines correspond to the theoretical values of t_ff/t_rot for spherical clouds of mass M_gas containing a star of mass M_⋆ at the center, in which the gas is rotationally supported against the gravity of both the gas plus the star (see Sect. 4.3). The two dotted black lines correspond to M_⋆ = 0 M_⊙ and 10 M_⊙. The blue dashed line indicates a mass of 50 M_⊙. The rotating structures with masses higher than this value are toroids.