Mid-$J$ CO Line Observations of Protostellar Outflows in the Orion Molecular Clouds

TL;DR

This study maps mid-$J$ CO lines in protostellar outflows within Orion, deriving physical parameters and comparing them with other CO transitions to understand outflow behaviors and their relation to protostellar properties.

Contribution

It provides new high-resolution observations of mid-$J$ CO lines in multiple protostellar outflows and compares these with low- and high-$J$ lines to distinguish different outflow components.

Findings

Mid-$J$ CO lines trace the same outflow component as low-$J$ lines.

High-$J$ CO emission is less correlated with kinetic luminosity, indicating different components.

Outflow strength correlates with bolometric luminosity and envelope mass.

Abstract

Ten protostellar outflows in the Orion molecular clouds were mapped in the $^{12}$CO/$^{13}$CO ${J=6\rightarrow5}$ and $^{12}$CO ${J=7\rightarrow6}$ lines. The maps of these mid-$J$ CO lines have an angular resolution of about 10$''$ and a typical field size of about 100$''$. Physical parameters of the molecular outflows were derived, including mass transfer rates, kinetic luminosities, and outflow forces. The outflow sample was expanded by re-analyzing archival data of nearby low-luminosity protostars, to cover a wide range of bolometric luminosities. Outflow parameters derived from other transitions of CO were compared. The mid-$J$ ($J_{\rm up} \approx 6$) and low-$J$ ($J_{\rm up} \leq 3$) CO line wings trace essentially the same outflow component. By contrast, the high-$J$ (up to $J_{\rm up} \approx 50$) line-emission luminosity of CO shows little correlation with the kinetic luminosity from the ${J=6\rightarrow5}$ line, which suggests that they trace distinct components. The low/mid-$J$ CO line wings trace long-term outflow behaviors while the high-$J$ CO lines are sensitive to short-term activities. The correlations between the outflow parameters and protostellar properties are presented, which shows that the strengths of molecular outflows increase with bolometric luminosity and envelope mass.