FAUST. II. Discovery of a Secondary Outflow in IRAS 15398-3359: Variability in Outflow Direction during the Earliest Stage of Star Formation?
Okoda, Y, Oya, Y, Francis, L, Johnstone, D, Inutsuka, S-I, Ceccarelli, C, Codella, C, Chandler, C, Sakai, N, Aikawa, Y, Alves, FO, Balucani, N, Bianchi, E, Bouvier, M, Caselli, P, Caux, E, Charnley, S, Choudhury, S, De Simone, M, Dulieu, F, Duran, A, Evans, L, Favre, C, Fedele, D, Feng, S, Fontani, F, Hama, T, Hanawa, T, Herbst, E, Hirota, T, Imai, M, Isella, A, Jimenez-Serra, I, Kahane, C, Lefloch, B, Loinard, L, Lopez-Sepulcre, A, Maud, LT, Maureira, MJ, Menard, F, Mercimek, S, Miotello, A, Moellenbrock, G, Mori, S, Murillo, NM, Nakatani, R, Nomura, H, Oba, Y, O'Donoghue, R, Ohashi, S, Ospina-Zamudio, J, Pineda, JE, Podio, L, Rimola, A, Sakai, T, Segura-Cox, D, Shirley, Y, Svoboda, B, Taquet, V, Testi, L, Vastel, C, Viti, S, Watanabe, N, Watanabe, Y, Witzel, A, Xue, C, Zhang, Y, Zhao, B, Yamamoto, S
Abstract
We have observed the very low-mass Class 0 protostar IRAS 15398−3359 at scales ranging from 50 to 1800 au, as part of the Atacama Large Millimeter/Submillimeter Array Large Program FAUST. We uncover a linear feature, visible in H_{2}CO, SO, and C^{18}O line emission, which extends from the source in a direction almost perpendicular to the known active outflow. Molecular line emission from H_{2}CO, SO, SiO, and CH_{3}OH 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 blueshifted with respect to the systemic velocity. A velocity gradient of 1.2 km s^{−1} over 1200 au along the linear feature seen in the H_{2}CO emission connects the protostar and the arc-like structure kinematically. SO, SiO, and CH_{3}OH 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.