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36 GHz methanol lines from nearby galaxies: maser or quasi-thermal emission?


Humire, PK and Henkel, C and Gong, Y and Leurini, S and Mauersberger, R and Levshakov, SA and Winkel, B and Tarchi, A and Castangia, P and Malawi, A and Asiri, H and Ellingsen, SP and McCarthy, TP and Chen, X and Tang, X, 36 GHz methanol lines from nearby galaxies: maser or quasi-thermal emission?, Astronomy and Astrophysics, 633 Article A106. ISSN 0004-6361 (2020) [Refereed Article]


Copyright Statement

Copyright P. K. Humire et al. 2020. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0)

DOI: doi:10.1051/0004-6361/201936330


Methanol (CH3OH) is one of the most abundant interstellar molecules, offering a vast number of transitions to be studied, including many maser lines. However, while the strongest Galactic CH3OH lines, the so-called class II masers, show no indications for the presence of superluminous counterparts in external galaxies, the less luminous Galactic class I sources appear to be different. Here we report class I 36 GHz (λ ≈ 0.8 cm) CH3OH 4−1 → 30 E line emission from the nearby galaxies Maffei 2 (D ≈ 6 Mpc) and IC 342 (D ≈ 3.5 Mpc), measured with the 100 m telescope at Effelsberg at three different epochs within a time span of about five weeks. The 36 GHz methanol line of Maffei 2 is the second most luminous among the sources detected with certainty outside the Local Group of galaxies. This is not matched by the moderate infrared luminosity of Maffei 2. Higher-resolution data are required to check whether this is related to its prominent bar and associated shocks. Upper limits for M 82, NGC 4388, NGC 5728 and Arp 220 are also presented. The previously reported detection of 36 GHz maser emission in Arp 220 is not confirmed. Nondetections are reported from the related class I 44 GHz (λ ≈ 0.7 cm) methanol transition towards Maffei 2 and IC 342, indicating that this line is not stronger than its 36 GHz counterpart. In contrast to the previously detected 36 GHz CH3OH emission in NGC 253 and NGC 4945, our 36 GHz profiles towards Maffei 2 and IC 342 are similar to those of previously detected nonmasing lines from other molecular species. However, by analogy to our Galactic center region, it may well be possible that the 36 GHz methanol lines in Maffei 2 and IC 342 are composed of a large number of faint and narrow maser features that remain spatially unresolved. In view of this, a search for a weak broad 36 GHz line component would also be desirable in NGC 253 and NGC 4945.

Item Details

Item Type:Refereed Article
Keywords:masers; galaxies: spiral; galaxies: individual: IC 342; galaxies: individual: Maffei 2; galaxies: ISM; radio lines: galaxies
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Cosmology and extragalactic astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Ellingsen, SP (Professor Simon Ellingsen)
UTAS Author:McCarthy, TP (Dr Tiege McCarthy)
ID Code:137052
Year Published:2020
Web of Science® Times Cited:4
Deposited By:Physics
Deposited On:2020-01-30
Last Modified:2021-01-27
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