Angular momentum profiles of Class 0 protostellar envelopes

Gaudel M.; Maury A.J.; Belloche A. & CALYPSO collab.

JANUARY 2020

In the framework of the IRAM CALYPSO survey, we obtained observations of the dense gas kinematics that we used to quantify the amount and distribution of specific angular momentum at all scales in collapsing-rotating Class 0 protostellar envelopes. We used the high dynamic range C18O (2−1) and N2H+(1−0) datasets to produce centroid velocity maps and probe therotational motions in the sample of 12 envelopes from scales∼50 to∼5000 au.



We identify differential rotation motions at scales.1600 au in 11 out of the 12 protostellar envelopes of our sample by measuring the velocity gradient along the equatorial axis, which we fit with a power-law model v∝r^α. This suggests that coherent motions dominate the kinematics in the inner protostellar envelopes. The radial distributions of specific angular momentum in the CALYPSO sample suggest the following two distinct regimes within protostellar envelopes: from the largest scales probed, the specific angular momentum decreases with decreasing radius as j∝r^1.6, down to∼1600 au and then tends to become relatively constant around a value ∼6×10^−4 km s−1pc down to∼50 au. The values of specific angular momentum measured in the inner Class 0 envelopes suggest that material directly involved in the star formation process (<1600 au) has a specific angular momentum on the same order of magnitude as what is inferred in small T-Tauri disks. Thus, disk formation appears to be a direct consequence of angular momentum conservation during the collapse. Our analysis reveals a dispersion of the directions of velocity gradients at envelope scales >1600 au, suggesting that these gradients may not be directly related to rotational motions of the envelopes. We conclude that the specific angular momentumobserved at these scales could find its origin in other mechanisms, such as core-forming motions (infall, turbulence), or trace an imprint of the initial conditions for the formation of protostellar cores.