ALMA Observations of the IRDC Clump G34.43+00.24 MM3: 278 GHz Class I Methanol Masers

TL;DR

This study uses ALMA to observe methanol masers in a molecular cloud, revealing their association with post-shocked gas and providing insights into shock conditions and maser origins.

Contribution

First high-resolution ALMA observations of 278 GHz Class I methanol masers in an IRDC, demonstrating their connection to post-shocked gas regions.

Findings

Methanol J_K=9_{-1}-8_0 E emission is masing.

Methanol masers originate from post-shocked gas in outflow regions.

Weak SiO emission suggests older or weaker shocks.

Abstract

We have observed a molecular clump (MM3) associated with the infrared dark cloud G34.43+00.24 in the CH3OH J_K=9_{-1}--8_0 E, 5_0-4_0 E, and 5_{-1}-4_{-1} E lines at sub-arcsecond resolution by using the Atacama Large Millimeter/submillimeter Array. By comparing the CH3OH J_K=9_{-1}-8_0 E emission with the CH3OH 5_0-4_0 E and 5_{-1}-4_{-1} E emission, we have found that the CH3OH J_K=9_{-1}-8_0 E emission is masing. We have clearly shown that the CH3OH J_K=9_{-1}-8_0 masers arise from the post shocked gas in the interacting regions between the outflows and ambient dense gas. Toward the strongest peak of the CH3OH maser emission, SiO J=6-5 emission is very weak. This indicates that the CH3OH maser emission traces relatively old shocks or weak shocks.