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tokens: the scales of r > 1600 au ( j app ∝ r 1.6 on average, see Table F.2 ), consistent with the prestellar stage ( j ∝ r 1.6 ). We discuss the properties and physical origin of these two regimes in more details in the next sections. 5.3 Conservation of angular momentum in Class 0 inner envelopes In this section, we focus on the relatively constant values of specific angular momentum observed in the inner envelopes at scales of r ≤ 1600 au in the j ( r ) profiles due to rotation motions (see Fig. 17 ). From these flat profiles, we find that the matter directly involved in the formation of the stellar embryo has a specific angular momentum ~3 orders of magnitude higher than the onein T-Tauri stars ( j ~ 2 × 10 −7 km s −1 pc, Bouvier et al. 1993 ). We discuss constant values of specific angular momentum as conservation of angular momentum to test disk formation as a possible solution to the angular momentum problem. It is difficult to constrain the time evolution of specific angular momentum for a given particle from angular momentum distributions which are snapshots of the angular momentum distribution of all particles at a given time during the collapse phase. During the collapse of a core initially in either solid-body rotation or differential rotation, particles conserve their specific angular momentum during the accretion on the stellar embryo ( Cassen Moosman 1981 ; Terebey et al. 1984 ; Goodwin et al. 2004 ). In the case of a protostellar envelope with a density profile ρ ∝ r −2 , an observed flat profile j ( r ) = constant requires, since each particle at different radii has the same specific angular momentum, an initially uniform distribution of angular momentum. This does not agree with the steep increase in specific angular momentum we observe at scales of r > 1600 au in the j ( r ) profiles. The break in the specific angular momentum profile could be due either to a faster collapse of the inner envelope caused by an initial inner density plateau ( Takahashi et al. 2016 ) or to a change of dominant mechanisms responsible for the observed velocity gradients from inner to outer scales of the envelope. In our sample, we distinguish eight sources with a relatively flat j ( r ) profile in the inner envelope ( β 0.5, see Table F.1 ): L1448-2A, L1448-NB, L1448-C, IRAS2A, SVS13-B, IRAS4B, L1527, and GF9-2. We estimate a centrifugal radius that would be obtained when the mass currently observed at ~100 au collapses and based on the mean value of specific angular momentum observed today ⟨ j 100 au ⟩ as follows: Table 4 Centrifugal radius R cent assuming angular momentum conservation. Notes. ( a ) Weighted mean of specific angular momentum in the inner envelopes (50 au r ≤ 1600 au). ( b ) Range of the object mass at 100 au, the minimum and maximum values are defined in Sect. 5.3 . ( c ) Centrifugal radii estimated from ⟨ j 100 au ⟩ and M 100 au using Eq. ( 2 ), assuming conservation of angular momentum. ( d ) Candidate disk radius determined from the