APEX CO (9-8) Mapping of an Extremely High-Velocity and Jet-like Outflow in a High-Mass Star-Forming Region

TL;DR

This study presents the first high-resolution CO (9-8) mapping of a high-mass star-forming region, revealing a highly-excited, collimated bipolar outflow driven by a protostar, and demonstrates the capabilities of new THz instrumentation.

Contribution

It provides the first THz line map of a molecular outflow, revealing detailed outflow structure and physical conditions in a high-mass star-forming region.

Findings

Revealed a jet-like, bipolar outflow in NGC 6334 I

Detected high-velocity line wings indicating gas temperatures >100 K

Showed the effectiveness of new THz receiver on APEX for high-quality mapping

Abstract

Atacama Pathfinder Experiment (APEX) mapping observations in CO (9-8) and (4-3) toward a high-mass star-forming region, NGC 6334 I, are presented. The CO (9-8) map has a 6.4 arcsec resolution, revealing a ~0.5 pc, jet-like, and bipolar outflow. This is the first map of a molecular outflow in a THz line. The CO (9-8) and (4-3) lines arising from the outflow lobes both show extremely high-velocity line wings, and their ratios indicate a gas temperature greater than 100 K and a density higher than 10^4 cm^{-3}. The spatial-velocity structure of the CO (9-8) data is typical of a bow-shock-driven flow, which is consistent with the association between the bipolar outflow and the infrared bow-shaped tips. In short, the observations unveil a highly-excited and collimated component in a bipolar outflow that is powered by a high-mass protostar, and provide insights into the driving mechanism of the outflow. Meanwhile, the observations demonstrate that high-quality mapping observations can be performed with the new THz receiver on APEX.