ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Evidence for a Molecular Jet Launched at an Unprecedented Early Phase of Protostellar Evolution
Sanhueza, Patricio; Kwon, Woojin; Soam, Archana; Johnstone, Doug; Kim, Kee-Tae; Lee, Chang Won; Lee, Chin-Fei; Lee, Jeong-Eun; Liu, Tie; Liu, Sheng-Yuan; Eden, David; Shang, Hsien; Yi, Hee-Weon; Li, Shanghuo; Zhang, Qizhou; Qin, Sheng-Li; Tatematsu, Ken'ichi; Traficante, Alessio; Kuan, Yi-Jehng; Evans, Neal J.; Juvela, Mika; Pelkonen, Veli-Matti; Goldsmith, Paul F.; Dutta, Somnath; Hirano, Naomi; Sahu, Dipen; Hsu, Shih-Ying; Bronfman, Leonardo; He, Jinhua; Luo, Qiuyi; Moraghan, Anthony; Jhan, Kai-Syun; Samal, Manash Ranjan; Liu, Hong-li
Taiwan, China, Canada, Japan, United States, South Korea, India, Italy, Finland, Chile, United Kingdom, Spain
Abstract
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.