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Southern class I methanol masers at 36 and 44 GHz


Voronkov, MA and Caswell, JL and Ellingsen, SP and Green, JA and Breen, SL, Southern class I methanol masers at 36 and 44 GHz, Monthly Notices of the Royal Astronomical Society, 439, (3) pp. 2584-2617. ISSN 0035-8711 (2014) [Refereed Article]

Copyright Statement

Copyright 2014 Oxford Universtiy Press

DOI: doi:10.1093/mnras/stu116


The Australia Telescope Compact Array (ATCA) has been used for high angular resolution imaging of 71 southern class I methanol maser sources quasi-simultaneously at 36 and 44 GHz. The data reveal a high level of morphological and kinematical complexity, and allow us to demonstrate associations, at arcsecond precision, of the class I maser emission with outflows, expanding H ɪɪ  regions, dark clouds, shocks traced by the 4.5-μm emission and 8.0-μm filaments. More than 700 maser component features were found at each of the two methanol transitions, but with only 23 per cent recognizable at both transitions; the morphology of class emission is much better revealed by our survey of both transitions, compared with either one alone. We found that the number of masers falls exponentially with the projected linear distance from the associated class II 6.7-GHz methanol maser. This distribution has a scale of 263 15 mpc, irrespective of the transition. The class I masers associated with OH masers were found to have a tendency to be more spread out, both spatially and in the velocity domain. This is consistent with the expectation that such sources are more evolved. Apart from a small number of high-velocity components (which are largely blueshifted and predominantly seen at 36 GHz), the velocity distribution was found to be Gaussian, peaking near the systemic velocity of the region, which had been estimated as the middle of the velocity interval of the associated class II methanol maser at 6.7 GHz. The mean indicated a small, but significant blueshift asymmetry of −0.57 km s−1 (uncertainties are 0.06 and 0.07 km s−1 for the 36- and 44-GHz masers, respectively) with respect to the 6.7-GHz masers. The standard deviation of the velocity distribution was found to be 3.65 0.05 and 3.32 0.07 km s−1 for the 36- and 44-GHz masers, respectively. We also suggest a refined rest frequency value of 36169.238 0.011 MHz for the 4−1-30 E methanol transition.

Item Details

Item Type:Refereed Article
Keywords:masers, stars: formation, HII regions, ISM: jets and outflows, ISM: molecules, photodissociation region (PDR)
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Galactic astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Voronkov, MA (Dr Maxim Voronkov)
UTAS Author:Ellingsen, SP (Professor Simon Ellingsen)
UTAS Author:Breen, SL (Dr Shari Breen)
ID Code:90104
Year Published:2014
Web of Science® Times Cited:71
Deposited By:Mathematics and Physics
Deposited On:2014-03-27
Last Modified:2017-11-01

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