The detection of spatially resolved protosteller outflows and episodic jets in the outer Galaxy

TL;DR

This study reports the first spatially resolved detection of protostellar outflows and episodic jets in the outer Galaxy, revealing similarities to inner Galaxy star formation and providing insights into low-metallicity environments.

Contribution

It presents the first ALMA observations of resolved protostellar outflows and jets in the outer Galaxy, highlighting episodic mass ejections and chemical differences from inner Galaxy sources.

Findings

Detected well-collimated outflows and jets with bullet structures.

Estimated episodic ejection intervals of 900-4000 years.

Found lower SiO/CO ratios suggesting different shock chemistry.

Abstract

We present the first detection of spatially resolved protostellar outflows and jets in the outer Galaxy. We observed five star-forming regions in the outer Galaxy (Sh 2--283, NOMF05-16/19/23/63; galactocentric distance = 15.7--17.4 kpc) with the Atacama Large Millimeter/submillimeter Array (ALMA). Towards Sh 2--283, we have detected distinct outflow ($\sim$5--50 km s$^{-1}$) and jet components ($\sim$50--100 km s$^{-1}$) associated with the protostar in CO(3--2) emission. The outflows and jets are well-collimated, with the jets exhibiting multiple bullet structures. The position-velocity diagram along the CO flow axis shows two characteristic structures: (a) the flow velocity which linearly increases with the position offset from the core center (Hubble-like flow), and (b) continuous velocity components of the periodical flows (spine-like structures), which may indicate the episodic mass-ejection event. The time intervals of the mass-ejection events are estimated to be 900--4000 years based on the slopes of these spine-like structures. These characteristics align with those of nearby protostellar systems, indicating that early star formation in low-metallicity environments, such as the outer Galaxy, resembles that in the inner Galaxy. In contrast to the physical similarities, the $N\mathrm{(SiO)}$/$N\mathrm{(CO)}$ ratio in the jet bullet appears to be lower than that measured in the low-mass protostellar sources in the inner Galaxy. This may indicate the different shock chemistry or different dust composition in the outer Galaxy source, although non-LTE effects could also affect the observed low $N\mathrm{(SiO)}$/$N\mathrm{(CO)}$ ratio. We also report the new detection of the other 4 outflow sources in the outer Galaxy.