Unveiling the Evolutionary Sequence from Infalling Envelopes to Keplerian Disks around Low-Mass Protostars

TL;DR

This study uses SMA observations of C18O emission to analyze the rotational motions of protostellar envelopes, revealing a progression from infalling envelopes with conserved angular momentum to Keplerian disks around low-mass protostars.

Contribution

It provides observational evidence of the evolutionary sequence from infalling envelopes to Keplerian disks, highlighting changes in rotational profiles across different protostellar stages.

Findings

Detection of rotational motions with different radial profiles.

Identification of transition from infalling envelopes to Keplerian disks.

Comparison with inside-out collapse models.

Abstract

We performed SMA 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 to 1000 AU scales. C18O (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 Vrot ~ 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 Vrot ~ 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.