An Observational Scenario of Keplerian Disk Formation around Protostars Revealed with the SMA and ALMA
In order to study the evolution from infalling and rotating envelopes to the formation of large-scale Keplerian disks, we have conducted Submillimeter Array observations of the inner part (100-1000 AU) of protostellar envelopes around a sample of Class 0 and I protostars. Our observations show that the kinematics of protostellar envelopes can be categorized into three groups, (1) infalling motion with little rotational motion around Class 0 protostars (e.g., B335 and NGC 1333 IRAS 4B), (2) both infalling and rotational motions around Class 0 and I protostars (e.g., L1448-mm and L1527 IRS), and (3) rotational motion without clear infalling motion around Class I protostars (e.g., TMC-1A and L1489 IRS). The three categories demonstrate the evolution from infalling envelopes to Keplerian disks. To reveal the connection between protostellar envelopes and disks, we have conducted ALMA observations toward L1489 IRS. A Keplerian disk is clearly seen in the 12CO (2-1) and C18O (2-1) emission. In addition, there are protrusions which are offset from the disk major axis and attached to the Keplerian disk. The kinematics of these protrusions cannot be explained by the Keplerian rotation. The evolution from infalling envelopes to Keplerian disks and the nature of the non-Keplerian protrusions will be discussed.