ALMA survey of Orion planck galactic cold clumps (ALMASOP): evidence for a molecular jet launched at an unprecedented early phase of protostellar evolution

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, entraininf an outflow from the infalling envelope. Until now, molecular jets have been observed at high velocity (greater than or similar to 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 (similar to 4.2 km s(-1), deprojected similar to 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 N2D+ 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 similar to 930(-100)(+200) yr. The spectral energy distribution also suggests a very young source having an upper limit of T-bol similar to 31 K and L-bol similar to 0.8 L-circle dot. 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.