Rotation of the NGC 1333 IRAS 4A2 Protostellar Jet

The bipolar jet of the NGC 1333 IRAS 4A2 protostar shows a velocity gradient in the direction perpendicular to the jet axis. This lateral velocity gradient can be seen throughout the jet imaged in a silicon monoxide line, 2500-8700 AU from the driving source, and is consistent with the rotation of the accretion disk. If this gradient is caused by the rotation of the jet around its axis, the average specific angular momentum is about 1.5 x 10^21 cm^2 s^-1. Comparison of the kinematics between the jet and the disk suggests that the jet-launching region on the disk has a radius of about 2 AU, which supports the disk-wind models. The angular momentum transported away by the jet seems to be large enough for the protostar to accrete matter from the disk, confirming the crucial role of jets in the early phase of star formation process.