We performed SMA observations in the C ^ { 18 } O ( 2–1 ) emission line toward six Class 0 and I protostars , to study rotational motions of their surrounding envelopes and circumstellar material on 100 to 1000 AU scales .
C ^ { 18 } O ( 2–1 ) emission with intensity peaks located at the protostellar positions is detected toward all the 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 } \propto r ^ { -1.0 \pm 0.2 } and \propto r ^ { -1.0 \pm 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 } \propto r ^ { -0.6 \pm 0.1 } and \propto r ^ { -0.5 \pm 0.1 } , respectively .
The rotational motions with the radial dependence of \sim r ^ { -1 } can be interpreted as rotation with a conserved angular momentum in a dynamically infalling envelope , while those with the radial dependence of \sim 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 .