Journal Article

ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Evidence for a Molecular Jet Launched at an Unprecedented Early Phase of Protostellar Evolution

Shang, Hsien, Lee, Chang Won, Sahu, Dipen, Lee, Chin-Fei, Kwon, Woojin, Traficante, Alessio, He, Jinhua, Moraghan, Anthony, Pelkonen, Veli-Matti, Kuan, Yi-Jehng, Yi, Hee-Weon, Eden, David, Lee, Jeong-Eun, Hirano, Naomi, Zhang, Qizhou, Jhan, Kai-Syun, Juvela, Mika, Sanhueza, Patricio, Kim, Kee-Tae, Li, Shanghuo, Evans, Neal J, Bronfman, Leonardo, Liu, Tie, Johnstone, Doug, Qin, Sheng-Li, Liu, Hong-li, Tatematsu, Ken’ichi, Goldsmith, Paul F, Luo, Qiuyi, Soam, Archana, Hsu, Shih-Ying, Liu, Sheng-Yuan, Samal, Manash Ranjan, Dutta, Somnath

2022

Overview

Protostellar outflows and jets play a vital role in star formation as they carry away excess angular momentum from the inner disk surface, allowing the material to be transferred toward the central protostar. Theoretically, low-velocity and poorly collimated outflows appear from the beginning of the collapse at the first hydrostatic core (FHSC) stage. With growing protostellar core mass, high-density jets are launched, entraining an outflow from the infalling envelope. Until now, molecular jets have been observed at high velocity (≳100 km s−1) in early Class 0 protostars. We, for the first time, detect a dense molecular jet in SiO emission with low velocity (∼4.2 km s−1, deprojected ∼24 km s−1) from source G208.89–20.04Walma (hereafter G208Walma) using ALMA Band 6 observations. This object has some characteristics of FHSCs, such as a small outflow/jet velocity, extended 1.3 mm continuum emission, and N 2D+ line emission. Additional characteristics, however, are typical of early protostars: collimated outflow and SiO jet. The full extent of the outflow corresponds to a dynamical timescale of ∼ 930−100+200 yr. The spectral energy distribution also suggests a very young source having an upper limit of T bol ∼ 31 K and L bol ∼ 0.8 L ⊙. We conclude that G208Walma is likely in the transition phase from FHSC to protostar, and the molecular jet has been launched within a few hundred years of initial collapse. Therefore, G208Walma may be the earliest object discovered in the protostellar phase with a molecular jet.

• Publisher: IOP Publishing
• Subject: Angular momentum / Continuum radiation / Jets / Outflow / Protostars / Spectral energy distribution / Star & galaxy formation / Star formation / Stellar evolution / Velocity