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

Rotating outflows from protostellar disks might trace extended magnetohydrodynamic (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 bow shock. Although it was theoretically predicted, this is the first time that such a jet–DW interaction has been 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 ≳4 au. Inside 4 au, where the DW may not exist, the magnetorotational instability might be transporting angular momentum outward. 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.