2013ApJ...772...22Y

We performed Submillimeter Array observations in the C¹⁸O (2-1) emission line toward six Class 0 and I protostars to study rotational motions of their surrounding envelopes and circumstellar material on 100-1000 AU scales. C¹⁸O (2-1) emission with intensity peaks located at the protostellar positions is detected toward all six sources. The rotational velocities of the protostellar envelopes as a function of radius were measured from the position-velocity diagrams perpendicular to the outflow directions passing through the protostellar positions. Two Class 0 sources, B335 and NGC 1333 IRAS 4B, show no detectable rotational motion, while L1527 IRS (Class 0/I) and L1448-mm (Class 0) exhibit rotational motions with radial profiles of V_rot∝r.^–1.0±0.2 and ∝r.^–1.0±0.1, respectively. The other Class I sources, TMC-1A and L1489 IRS, exhibit the fastest rotational motions among the sample, and their rotational motions have flatter radial profiles of V_rot∝r ^–0.6±0.1 and ∝r ^–0.5±0.1, respectively. The rotational motions with the radial dependence of ∼r.^–1 can be interpreted as rotation with a conserved angular momentum in a dynamically infalling envelope, while those with the radial dependence of ∼r ^–0.5 can be interpreted as Keplerian rotation. These observational results demonstrate categorization of rotational motions from infalling envelopes to Keplerian-disk formation. Models of the inside-out collapse where the angular momentum is conserved are discussed and compared with our observational results.