Alma Observations of Infalling Flows Toward the Keplerian Disk Around the Class I Protostar L1489 Irs

Abstract

We have conducted ALMA observations in the 1.3 mm continuum and 12 CO (2-1), C 18 O (2-1) and SO (5 6 -4 5 ) lines toward L1489 IRS, a Class I protostar surrounded by a Keplerian disk and an infalling envelope. The Keplerian disk is clearly identified in the 12 CO and C 18 O emission, and its outer radius (∼700 AU) and mass (∼0.005 M ⊙ ) are comparable to those of disks around T Tauri stars. The protostellar mass is estimated to be 1.6 M ⊙ with the inclination angle of 66 • . In addition to the Keplerian disk, there are blueshifted and redshifted off-axis protrusions seen in the C 18 O emission pointing toward the north and the south, respectively, adjunct to the middle part of the Keplerian disk. The shape and kinematics of these protrusions can be interpreted as streams of infalling flows with a conserved angular momentum following parabolic trajectories toward the Keplerian disk, and the mass infalling rate is estimated to be ∼5 × 10 −7 M ⊙ yr −1 . The specific angular momentum of the infalling flows (∼2.5 × 10 −3 km s −1 pc) is comparable to that at the outer radius of the Keplerian disk (∼4.8 × 10 −3 km s −1 pc). The SO emission is elongated along the disk major axis and exhibits a linear velocity gradient along the axis, which is interpreted as that the SO emission

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A Face-on Accretion System in High-mass Star Formation: Possible Dusty Infall Streams within 100 AU

“…Three-dimensional structure is clearly required rather than a planar disk-like system, given the nearly face-on geometry. Alternatively, such a non-axisymmetric structure evokes the infall streams found in several low-mass protostars and protobinaries (e.g., Mayama et al 2010;Casassus et al 2013;Tang et al 2014;Yen et al 2014). In particular, recent ALMA observations toward a low-mass class 0 object have found that similar non-axisymmetric streams fall down onto the edge-on accretion disk along a parabolic orbit (Yen et al 2014).…”