Disentangling the jet emission from protostellar systems. The ALMA view of VLA1623

Abstract

Context: High-resolution studies of class 0 protostars represent the key to constraining protostar formation models. VLA16234-2417 represents the prototype of class 0 protostars, and it has been recently identified as a triple non-coeval system. Aim: We aim at deriving the physical properties of the jets in VLA16234-2417 using tracers of shocked gas. Methods: ALMA Cycle 0 Early Science observations of CO(2-1) in the extended configuration are presented in comparison with previous SMA CO(3-2) and Herschel-PACS [OI}] 63 micron observations. Gas morphology and kinematics were analysed to constrain the physical structure and origin of the protostellar outflows. Results: We reveal a collimated jet component associated with the [OI] 63 micron emission at about 8'' (about 960 AU) from source B. This newly detected jet component is inversely oriented with respect to the large-scale outflow driven by source A, and it is aligned with compact and fast jet emission very close to source B (about 0.3'') rather than with the direction perpendicular to the A disk. We also detect a cavity-like structure at low projected velocities, which surrounds the [OI] 63 micron emission and is possibly associated with the outflow driven by source A. Finally, no compact outflow emission is associated with source W. Conclusions: Our high-resolution ALMA observations seem to suggest there is a fast and collimated jet component associated with source B. This scenario would confirm that source B is younger than A, that it is in a very early stage of evolution, and that it drives a faster, more collimated, and more compact jet with respect to the large-scale slower outflow driven by A. However, a different scenario of a precessing jet driven by A cannot be firmly excluded from the present observations.