Mid-J CO emission from the Orion BN/KL explosive outflow

TL;DR

This study investigates the high-J CO emission from the Orion BN/KL explosive outflow, revealing shock excitation and estimating its kinetic energy, supporting the explosive event hypothesis related to dynamic decay.

Contribution

It provides high-resolution observations of higher-J CO lines in Orion BN/KL, linking outflow features to explosive events and shock excitation, which were not previously characterized in this detail.

Findings

High-J CO emission aligns with low-J data, indicating shock excitation.

Estimated kinetic energy of the outflow is 1-2x10^47 erg.

Proposed scenario of outflow deceleration explaining methanol masers.

Abstract

High spatial resolution low-J 12CO observations have shown that the wide-angle outflow seen in the Orion BN/KL region correlates with the famous H2 fingers. Recently, high-resolution large-scale mappings of mid- and higher-J CO emissions have been reported toward the Orion molecular cloud 1 core region using the APEX telescope. Therefore, it is of interest to investigate this outflow in the higher-J 12CO emission, which is likely excited by shocks. The observations were carried out using the dual-color heterodyne array CHAMP+ on the APEX telescope. The images of the Orion BN/KL region were obtained in the 12CO J=6-5 and J=7-6 transitions with angular resolutions of 8.6 and 7.4 arcsec, respectively. The results show a good agreement between our higher-J 12CO emission and SMA low-J 12CO data, which indicates that this wide-angle outflow in Orion BN/KL is likely the result of an explosive event that is related to the runaway objects from a dynamically decayed multiple system. From our observations, we estimate that the kinetic energy of this explosive outflow is about 1-2x10^47 erg. In addition, a scenario has been proposed where part of the outflow is decelerated and absorbed in the cloud to explain the lack of CO bullets in the southern part of BN/KL, which in turn induces the methanol masers seen in this region.