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

TL;DR

This paper reports the detection of a highly luminous 36 GHz methanol maser in NGC 4945, indicating large-scale shocks in molecular gas possibly linked to early star formation stages.

Contribution

First detection of 36 GHz methanol maser emission in NGC 4945, revealing extragalactic class I masers trace large-scale shocks and star formation processes.

Findings

Detected 36.2 GHz methanol emission offset from nucleus

Emission is narrow and highly luminous, indicating maser activity

Extragalactic masers trace large-scale shocks, not just luminous Galactic analogs

Abstract

We have searched for emission from the 36.2 GHz ($4_{-1} \rightarrow 3_0$E) methanol transition towards NGC 4945, using the Australia Telescope Compact Array. 36.2 GHz methanol emission was detected offset south-east from the Galactic nucleus. The methanol emission is narrow, with a linewidth <10 kms$^{-1}$, 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 $\sim90$ more luminous than the widespread emission detected from the Milky Way central molecular zone (CMZ). 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.