FAUST II. Discovery of a Secondary Outflow in IRAS 15398-3359: Variability in Outflow Direction during the Earliest Stage of Star Formation?

Abstract

We have observed the very low-mass Class 0 protostar IRAS 15398-3359 at scales ranging from 50 au to 1800 au, as part of the ALMA Large Program FAUST. We uncover a linear feature, visible in H2CO, SO, and C18O line emission, which extends from the source along a direction almost perpendicular to the known active outflow. Molecular line emission from H2CO, SO, SiO, and CH3OH further reveals an arc-like structure connected to the outer end of the linear feature and separated from the protostar, IRAS 15398-3359, by 1200 au. The arc-like structure is blue-shifted with respect to the systemic velocity. A velocity gradient of 1.2 km/s over 1200 au along the linear feature seen in the H2CO emission connects the protostar and the arc-like structure kinematically. SO, SiO, and CH3OH are known to trace shocks, and we interpret the arc-like structure as a relic shock region produced by an outflow previously launched by IRAS 15398-3359. The velocity gradient along the linear structure can be explained as relic outflow motion. The origins of the newly observed arc-like structure and extended linear feature are discussed in relation to turbulent motions within the protostellar core and episodic accretion events during the earliest stage of protostellar evolution.

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• Chemical and Physical Characterization of the Isolated Protostellar Source CB68: FAUST. IV
• Evolution of the Angular Momentum of Molecular Cloud Cores Formed from Filament Fragmentation
• FAUST VII. Detection of A Hot Corino in the Prototypical Warm Carbon-Chain Chemistry Source IRAS 15398-3359
• Cloudlet Capture Model for Asymmetric Molecular Emission Lines Observed in TMC-1A with ALMA
• Origin and Evolution of Angular Momentum of Class II Disks
• FAUST XXVI. The dust opacity spectral indices of protostellar envelopes bridge the gap between interstellar medium and disks
• Synthetic Observations of the Infalling Rotating Envelope: Links between the Physical Structure and Observational Features
• Episodicity in accretion-ejection processes associated with IRAS 15398-3359
• FAUST XXV. A potential new molecular outflow in [BHB2007] 11
• The JCMT Transient Survey: Four Year Summary of Monitoring the Submillimeter Variability of Protostars