Detection of 36 GHz Class I Methanol Maser Emission toward NGC 4945

Abstract

Abstract We have searched for emission from the 36.2 GHz ( 4 − 1 → 3 0 E ) methanol transition toward NGC 4945, using the Australia Telescope Compact Array. 36.2 GHz methanol emission was detected offset southeast from the Galactic nucleus. The methanol emission is narrow, with a line width <10 km s−1 and a luminosity five orders of magnitude higher than Galactic class I masers from the same transition. These characteristics combined the with physical separation from the strong central thermal emission suggests that the methanol emission is a maser. This emission is a factor of ∼90 more luminous than the widespread emission detected from the Milky Way central molecular zone. This is the fourth detection of extragalactic class I emission and the third detection of extragalactic 36.2 GHz maser emission. These extragalactic class I methanol masers do not appear to be simply highly luminous variants of Galactic class I emission and instead appear to trace large-scale regions of low-velocity shocks in molecular gas, which may precede, or be associated with, the early stages of large-scale star formation.