The almost ubiquitous association of 6.7-GHz methanol masers with dust

Urquhart, J. S and Moore, T. J. T. and Menten, K. M. and König, C. and Wyrowski, F. and Csengeri, Tímea (2015) The almost ubiquitous association of 6.7-GHz methanol masers with dust. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 446 (4). pp. 3461-3477. ISSN 0035-8711

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Abstract

We report the results of 870-μmcontinuum observations, using the Large APEX Bolome- ter Camera (LABOCA), towards 77 class-II, 6.7-GHz methanol masers identified by the Methanol Multibeam (MMB) survey to map the thermal emission from cool dust towards these objects. These data complement a study of 630 methanol masers associated with com- pact dense clumps identified from the ATLASGAL survey. Compact dust emission is detected towards 70 sources, which implies a dust-association rate of 99 per cent for the full MMB cat- alogue. Evaluation of the derived dust and maser properties leads us to conclude that the combined sample represents a single population tracing the same phenomenon. We find me- dian clump masses of a few 103 M⊙ and that all but a handful of sources satisfy the mass-size criterion required for massive star formation. This study provides the strongest evidence of the almost ubiquitous association of methanol masers with massive, star-forming clumps. The fraction of methanol-maser associated clumps is a factor of ∼2 lower in the outer Galaxy than the inner Galaxy, possibly a result of the lower metallicity environment of the former. We find no difference in the clump-mass and maser-luminosity distributions of the inner and outer Galaxy. The maser-pumping and clump-formation mechanisms are therefore likely to be relatively invariant to Galactic location. Finally, we use the ratio of maser luminosity and clump mass to investigate the hypothesis that the maser luminosity is a good indicator of the evolutionary stage of the embedded source, however, we find no evidence to support this.

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