Detection of 36 GHz class I methanol maser emission towards NGCS253

TL;DR

This paper reports the first detection of 36 GHz class I methanol maser emission in a galaxy outside the Milky Way, suggesting it could be a new tool for studying starburst galaxies and fundamental constants.

Contribution

It presents the first evidence of extragalactic 36 GHz methanol maser emission, expanding the understanding of masers beyond our galaxy.

Findings

Detected two regions of methanol emission in NGC253.

Emission characteristics suggest it is likely a maser.

Emission is significantly more luminous than Galactic counterparts.

Abstract

We have used the Australia Telescope Compact Array (ATCA) to search for emission from the $4_{-1} \rightarrow 3_{0}E$ transition of methanol (36.2 GHz) towards the center of the nearby starburst galaxy NGC253. Two regions of emission were detected, offset from the nucleus along the same position angle as the inner spiral arms. The emission is largely unresolved on a scale of 5 arcsec, has a full-width half maximum (FWHM) line width of < 30 km s$^{-1}$, and an isotropic luminosity orders of magnitude larger than that observed in any Galactic star formation regions. These characteristics suggest that the 36.2 GHz methanol emission is most likely a maser, although observations with higher angular and spectral resolution are required to confirm this. If it is a maser this represents the first detection of a class I methanol maser outside the Milky Way. The 36.2 GHz methanol emission in NGC253 has more than an order of magnitude higher isotropic luminosity than the widespread emission recently detected towards the center of the Milky Way. If emission from this transition scales with nuclear star formation rate then it may be detectable in the central regions of many starburst galaxies. Detection of methanol emission in ultra-luminous infra-red galaxies (ULIRGs) would open up a new tool for testing for variations in fundamental constants (in particular the proton-to-electron mass ratio) on cosmological scales.