CSO CO(2-1) and Spitzer IRAC Observations of a Bipolar Outflow in High-mass Star-forming Region IRAS 22506+5944

TL;DR

This study combines CO (2-1) and Spitzer IRAC observations to analyze a bipolar outflow in a high-mass star-forming region, revealing bow-shocks and supporting a jet bow-shock driven outflow model.

Contribution

It provides new multi-wavelength evidence for bow-shock driven outflows in IRAS 22506+5944, including CO line ratio analysis and outflow mass spectrum fitting.

Findings

Detection of a bipolar outflow with bow-shaped tips in IRAS 22506+5944.

CO (2-1)/(1-0) line ratio varies with velocity, supporting bow-shock driven outflow.

Mass spectrum analysis favors the jet bow-shock model over the wide-angle wind model.

Abstract

We present Caltech Submillimeter Observatory CO (2-1) and Spitzer IRAC observations toward IRAS 22506+5944, which is a 10$^4$ $L_{\odot}$ massive star-forming region. The CO (2-1) maps show an east-west bipolar molecular outflow originating from the 3 mm dust continuum peak. The Spitzer IRAC color-composite image reveals a pair of bow-shaped tips which are prominent in excess 4.5 $\mu$m emission and are located to the leading fronts of the bipolar outflow, providing compelling evidence for the existence of bow-shocks as the driving agents of the molecular outflow. By comparing our CO (2-1) observations with previously published CO (1-0) data, we find that the CO (2-1)/(1-0) line ratio increases from low (~5 km s$^{-1}$) to moderate (~8 - 12 km s$^{-1}$) velocities, and then decreases at higher velocities. This is qualitatively consistent with the scenario that the molecular outflow is driven by multiple bow-shocks. We also revisit the position-velocity diagram of the CO (1-0) data, and find two spur structures along the outflow axis, which are further evidence for the presence of multiple jet bow-shocks. Finally, power-law fittings to the mass spectrum of the outflow gives power law indexes more consistent with the jet bow-shock model than the wide-angle wind model.