Super-fast Rotation in the OMC 2/FIR 6b Jet

TL;DR

This paper reports the discovery of an exceptionally fast-rotating protostellar jet in Orion, with high angular momentum and a large launching radius, supporting a magnetohydrodynamic disk wind origin.

Contribution

It provides the first detailed measurement of rapid jet rotation and angular momentum in the FIR 6b protostar, linking observations with disk wind theory.

Findings

Jet rotation velocity exceeds 20 km/s.

Specific angular momentum is greater than 10^22 cm^2/s.

Jet launching radius estimated between 2.18 and 2.96 au.

Abstract

We present ALMA CO ($J$=2--1) and 1.3 mm continuum observations of the high-velocity jet associated with the FIR 6b protostar located in the Orion Molecular Cloud-2. We detect a velocity gradient along the short axis of the jet in both the red- and blue-shifted components. The position-velocity diagrams along the short axis of the red-shifted jet show a typical characteristic of a rotating cylinder. We attribute the velocity gradient in the red-shifted component to rotation of the jet. The rotation velocity ($>20\,\ \rm{km s^{-1}}$) and specific angular momentum ($>10^{22}\, \rm{cm^{2}\, s^{-1}}$) of the jet around FIR 6b are the largest among all jets in which rotation has been observed. By combining disk wind theory with our observations, the jet launching radius is estimated to be in the range of $2.18-2.96$\,au. The rapid rotation, large specific angular momentum, and a launching radius far from the central protostar can be explained by a magnetohydrodynamic disk wind that contributes to the angular momentum transfer in the late stages of protostellar accretion.