2014ApJ...794L..10Y

We have observed a molecular clump (MM3) associated with the infrared dark cloud G34.43+00.24 in the CH₃ OH J_K= 9_–1-8₀E, 5₀-4₀E, and 5_–1-4_–1E lines at sub-arcsecond resolution by using the Atacama Large Millimeter/submillimeter Array. By comparing the CH₃OH J_K= 9_–1-8₀E emission with the CH₃OH 5₀-4₀E and 5_–1-4_–1E emission, we have found that the CH₃OH J_K= 9_–1-8₀E emission is masing. We have clearly shown that the CH₃OH J_K= 9_–1-8₀masers 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.