Infall and Rotation Motions in the HH 111 Protostellar System: A Flattened Envelope in Transition to a Disk?

Abstract

We have mapped the central region of the HH 111 protostellar system in 1.33 mm continuum, C¹⁸O (J = 2 - 1), ¹³CO (J = 2 - 1), and SO (N_J = 5₆ - 4₅) emissions at ~3'' resolution with the Submillimeter Array. There are two sources, VLA 1 (=IRAS 05491+0247) and VLA 2, with the VLA 1 source driving the HH 111 jet. Thermal emission is seen in 1.33 mm continuum tracing the dust in the envelope and the putative disks around the sources. A flattened, toruslike envelope is seen in C¹⁸O and ¹³CO around the VLA 1 source surrounding the dust lane perpendicular to the jet axis, with an inner radius of ~400 AU (1''), an outer radius of ~3200 AU (8''), and a thickness of ~1000 AU (2farcs5). It seems to be infalling toward the center with the conservation of specific angular momentum rather than with a Keplerian rotation as assumed by Yang et al. An inner envelope is seen in SO, with a radius of ~500 AU (1farcs3). The inner part of this inner envelope, which is spatially coincident with the dust lane, seems to have a differential rotation and thus may have formed a rotationally supported disk. The outer part of this inner envelope, however, may have a rotation velocity decreasing toward the center and thus represent a region where an infalling envelope is in transition to a rotationally supported disk. A brief comparison with a collapsing model suggests that the flattened, toruslike envelope seen in C¹⁸O and ¹³CO could result from a collapse of a magnetized rotating toroid.