First Detection of Interaction between a Magnetic Disk Wind and an Episodic Jet in a Protostellar System

TL;DR

This paper reports the first direct observation of an interaction between a magnetic disk wind and an episodic jet in a protostellar system, providing new insights into angular momentum transfer in star formation.

Contribution

It presents the first resolved observation of a jet-disk wind interaction in HH 212, confirming theoretical predictions and elucidating the role of MHD disk winds in angular momentum extraction.

Findings

The wide-angle outflow is an extended MHD disk wind dominating angular momentum removal.

The inner launching radius of the disk wind is truncated to ≥4 au.

The jet-disk wind interaction can be used to probe magnetic fields in protostellar disks.

Abstract

Rotating outflows from protostellar disks might trace extended magneto-hydrodynamic (MHD) disk winds (DWs), providing a solution to the angular momentum problem in disk accretion for star formation. In the jet system HH 212, a rotating outflow was detected in SO around an episodic jet detected in SiO. Here we spatially resolve this SO outflow into three components: a collimated jet aligned with the SiO jet, the wide-angle disk outflow, and an evacuated cavity in between created by a large jet-driven bowshock. Although it was theoretically predicted before, it is the first time that such a jet-DW interaction is directly observed and resolved, and it is crucial for the proper interpretation and modeling of non-resolved DW candidates. The resolved kinematics and brightness distribution both support the wide-angle outflow to be an extended MHD DW dominating the local angular momentum extraction out to 40 au, but with an inner launching radius truncated to $\gtrsim 4$ au. Inside 4 au, where the DW may not exist, the magneto-rotational instability (MRI) might be transporting angular momentum outwards. The jet-DW interaction in HH 212, potentially present in other similar systems, opens an entirely new avenue to probe the large-scale magnetic field in protostellar disks.