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We have used the Australia Telescope Compact Array to search for emission from the 4_–1 → 3₀ E transition of methanol (36.2 GHz) toward 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 FWHM line width of <30 km s^–1, and an isotropic luminosity orders of a magnitude larger than that observed in any Galactic star formation region. 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 toward the center of the Milky Way. If emission from this transition scales with the nuclear star formation rate, then it may be detectable in the central regions of many starburst galaxies. Detection of methanol emission in ultra-luminous infrared galaxies would open up a new tool for testing for variations in fundamental constants (particularly the proton-to-electron mass ratio) on cosmological scales.

Item Type:	Refereed Article
Keywords:	galaxies, individual (NGC 253) – galaxies, starburst – masers – radio lines, ISM
Research Division:	Physical Sciences
Research Group:	Astronomical and Space Sciences
Research Field:	Cosmology and Extragalactic Astronomy
Objective Division:	Expanding Knowledge
Objective Group:	Expanding Knowledge
Objective Field:	Expanding Knowledge in the Physical Sciences
Author:	Ellingsen, SP (Professor Simon Ellingsen)
ID Code:	93624
Year Published:	2014
Web of Science® Times Cited:	10
Deposited By:	Mathematics and Physics
Deposited On:	2014-08-10
Last Modified:	2017-11-03
Downloads:	243 View Download Statistics