Detection of Infall Motion from the Circumstellar Disk Associated with the Exciting Source of HH 111

Abstract

Results from high-resolution interferometric observations toward the exciting source of the highly collimated bipolar jet HH 111 in the CS (2-1) line and 98 GHz continuum are presented. Intense emission in both the line and the continuum has been detected. The continuum emission at 98 GHz is peaked at the VLA source detected by Rodriguez & Reipurth, while the peak of CS emission is shifted 2'' to the west, consistent with the earlier 13CO observation by Stapelfeldt & Scoville. Detailed velocity structure of the molecular gas has been revealed under the high velocity resolution of this observation. A molecular disk with an observed extent of ~0.04 pc (=8 × 103 AU) and a total velocity range of 2.9 km s-1 around the exciting source of HH 111 is identified from both the morphological and the velocity structures of the CS emission. This disk, resolved at different velocity channels, is oriented almost perpendicular to the collimated optical jet and to the previously known bipolar molecular outflow, and its direction of rotation has been determined. The velocity fields of the disk can be explained in terms of both infall and rotation motions in the disk plane. From the comparison between the observed velocity fields and those expected from simple kinematic models that involve both infall and rotation, the observed velocities can be fitted approximately by an infall component parameterized as Vr = -0.5/(r/15'')1/2 km s-1 and a lower amplitude rotating component as V = 0.3/(r/15'')1/2 km s-1. The disk infall rate deduced from the observed quantities is 6.9 × 10-6 M☉ yr-1, comparable to the accretion rate to the central star at the current epoch. The orientation of the molecular disk with respect to the collimated optical jet of HH 111 suggests that the infalling disk is associated with the driving source of HH 111. Additional support of this conclusion comes from the identification of a blueshifted outflow component of CS along the direction of the 12CO molecular outflow associated with HH 111.