Searching for kinematic evidence of Keplerian disks around Class 0
  protostars with CALYPSO
  The formation of protoplanetary disks is not well understood. To understand
how and when these disks are formed, it is crucial to characterize the
kinematics of the youngest protostars at a high angular resolution. Here we
study a sample of 16 Class 0 protostars to measure their rotation profile at
scales from 50 to 500~au and search for Keplerian rotation. We used
high-angular-resolution line observations obtained with the Plateau de Bure
Interferometer as part of the CALYPSO large program. From $\mathrm{^{13}CO}$
($J=2-1$), $\mathrm{C^{18}O}$ ($J=2-1$) and SO ($N_{j}=5_{6}-4_{5}$) moment
maps, we find that seven sources show rotation about the jet axis at a few
hundred au scales: SerpS-MM18, L1448-C, L1448-NB, L1527, NGC1333- IRAS2A,
NGC1333-IRAS4B, and SVS13-B. We analyzed the kinematics of these sources in the
$uv$ plane to derive the rotation profiles down to 50~au scales. We find
evidence for Keplerian rotation in only two sources, L1527 and L1448-C.
Overall, this suggests that Keplerian disks larger than 50 au are uncommon
around Class 0 protostars. However, in some of the sources, the line emission
could be optically thick and dominated by the envelope emission. Due to the
optical thickness of these envelopes, some of the disks could have remained
undetected in our observations.
