We have used the Australia Telescope Compact Array (ATCA) to search for emission from the 4 −1 → 3 0 E transition of methanol (36.2 GHz) towards the center of the nearby starburst galaxy NGC 253. 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 ′′ , 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 NGC 253 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.

We present the unambiguous discovery of six new class II methanol maser transitions, three of which are torsionally excited (v t =1). The newly discovered 6.18-GHz 17 2 → 18 3 E (v t =1), 7.68-GHz 12 4 → 13 3 A − (v t =0), 7.83-GHz 12 4 → 13 3 A + (v t = 0), 20.9-GHz 10 1 → 11 2 A + (v t =1), 44.9-GHz 2 0 → 3 1 E (v t =1) and 45.8-GHz 9 3 → 10 2 E (v t =0) methanol masers were detected towards G 358.931−0.030, where the known 6.68-GHz maser has recently been reported to be undergoing a period flaring. The detection of the v t =1 torsionally excited lines corroborates one of the missing puzzle pieces in class II maser pumping, but the intensity of the detected emission provides an additional challenge, especially in the case of the very highly excited 6.18-GHz line. Together with the newly detected v t = 0 lines, these observations provide significant new information which can be utilised to improve class II methanol maser modelling. We additionally present detections of 6.68-, 19.9-, 23.1-and 37.7-GHz class II masers, as well as 36.2-and 44.1-GHz class I methanol masers, and provide upper limits for the 38.3-and 38.5-GHz class II lines. Near simultaneous Australia Telescope Compact Array (ATCA) observations confirm that all 10 of the class II methanol maser detections are co-spatial to ∼0.2 arcsec, which is within the uncertainty of the observations. We find significant levels of linearly polarised emission in the 6.18-, 6.67-, 7.68-, 7.83-, 20.9-, 37.7-, 44.9-and 45.8-GHz transitions, and low levels of circular polarisation in the 6.68-, 37.7-and 45.8-GHz transitions.

We have searched for emission from the 36.2 GHz (  -4 3 E 1 0 ) 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.