Detection of a methanol megamaser in a major-merger galaxy

Abstract

We have detected emission from both the 4_{-1}-3_{0} E (36.2~GHz) class I and 7_{-2}-8_{-1} E (37.7~GHz) class II methanol transitions towards the centre of the closest ultra-luminous infrared galaxy Arp 220. The emission in both the methanol transitions show narrow spectral features and have luminosities approximately 8 orders of magnitude stronger than that observed from typical class I methanol masers observed in Galactic star formation regions. The emission is also orders of magnitude stronger than the expected intensity of thermal emission from these transitions and based on these findings we suggest that the emission from the two transitions are masers. These observations provides the first detection of a methanol megamaser in the 36.2 and 37.7 GHz transitions and represents only the second detection of a methanol megamaser, following the recent report of an 84 GHz methanol megamaser in NGC1068. We find the methanol megamasers are significantly offset from the nuclear region and arise towards regions where there is Ha emission, suggesting that it is associated with starburst activity. The high degree of correlation between the spatial distribution of the 36.2 GHz methanol and X-ray plume emission suggests that the production of strong extragalactic class I methanol masers is related to galactic outflow driven shocks and perhaps cosmic rays. In contrast to OH and H2O megamasers which originate close to the nucleus, methanol megamasers provide a new probe of feedback (e.g. outflows) processes on larger-scales and of star formation beyond the circumnuclear starburst regions of active galaxies.

Accepted for publication in ApJL

References in corpus (7)

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• The 6-GHz Multibeam Maser Survey I. Techniques
• P-Cygni Profiles of Molecular Lines toward Arp 220 Nuclei
• High-Resolution Radio Continuum Measurements of the Nuclear Disks of Arp 220
• The Arecibo Arp 220 Spectral Census I: Discovery of the Pre-Biotic Molecule Methanimine and New Cm-wavelength Transitions of Other Molecules
• Detection of 36 GHz class I methanol maser emission towards NGCS253
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Cited by in corpus (11)

• Online Database of Class I Methanol Masers
• Detection of 36 GHz class I methanol maser emission towards NGCS253
• Class I methanol masers in NGC253: Alcohol at the end of the bar
• Methanol masers in NGC 253 with ALCHEMI
• MALT-45: A 7mm survey of the southern Galaxy - II. ATCA follow-up observations of 44GHz class I methanol masers
• Discovery of Methanimine Megamasers Toward Compact Obscured Galaxy Nuclei
• 36 GHz methanol lines from nearby galaxies: maser or quasi-thermal emission?
• Astrophysical constraints on the proton-to-electron mass ratio with FAST
• Variability in extragalactic class I methanol masers: New maser components toward NGC4945 and NGC253
• A sensitive search for predicted methanol maser transitions with the Australia Telescope Compact Array
• Dark matter halos of luminous AGNs from galaxy-galaxy lensing with the HSC Subaru Strategic Program