Work

A high-velocity SiO jet from S255N SMA3

Year: 2026

Type: article

Abstract: ABSTRACT We present Atacama Large Millimeter/subillimeter Array (ALMA) Band 6 observations of the compact source SMA3 in the S255IR region, analysing both SiO (J = 5−4, 6−5) and CS (J = 5−4) emission to characterize the structure and kinematics of its outflow. The data reveal a highly collimated bipolar jet traced by SiO, reaching line-of-sight velocities of up to $\pm$60 km s$^{-1}$ and deprojected velocities of $\pm \sim$80 km s$^{-1}$, with a collimation ratio of $\sim$4.7 over a spatial extent of $\sim$5800 au. The inferred dynamical age is 343 yr. Position–velocity diagrams exhibit a continuous velocity structure with triangular morphology, consistent with a steady disc wind rather than an episodic or X-wind-driven flow. Excitation analysis yields a characteristic SiO temperature of $\sim$42 K, and we derive the jet mass, momentum, and kinetic energy which are indicative of a dense, mass-loaded molecular outflow. The emission shows clear chemical and kinematic differentiation: SiO traces the high-velocity jet spine, while CS is observed at lower velocities close to the protostar, and only reaches high velocities at larger distances. Despite forming within a clustered high-mass star-forming region, the jet exhibits a high degree of symmetry, collimation, and dynamical coherence more commonly associated with protostars forming in isolation or less crowded star-forming regions. This demonstrates that well-ordered, narrowly collimated, disc-driven jets can be launched and maintained even in the dense, competitive environments characteristic of high-mass star formation.

Source: Monthly Notices of the Royal Astronomical Society

DOI: 10.1093/mnras/stag1645

Authors: P D Klaassen, M Reiter, Y Zhang, K E I Tanaka, A E Guzman