Spectral Energy Distributions of 6.7 GHz methanol masers

Abstract

The 6.7 GHz maser transition of methanol has been found exclusively towards massive star forming regions. A majority of the masers have been found to lack the presence of any associated radio continuum. This could be due to the maser emission originating prior to the formation of an HII region around the central star, or from the central object being too cool to produce a HII region. One way to distinguish between the two scenarios is to determine and model the spectral energy distributions (SEDs) of the masers. We observed a sample of 20 6.7 GHz methanol masers selected from the blind Arecibo survey, from centimeter to submillimeter wavelengths. We combined our observations with existing data from various Galactic plane surveys to determine SEDs from centimeter to near-infrared wavelengths. We find that 70% of the masers do not have any associated radio continuum, with the rest of the sources being associated with hypercompact and ultracompact HII regions. Modeling the SEDs shows them to be consistent with rapidly accreting massive stars, with accretion rates well above 10^{-3} M_sun/yr. The upper limits on the radio continuum are also consistent with any ionized region being confined close to the stellar surface. This confirms the paradigm of 6.7 GHz methanol masers being signposts of early phases of massive star formation, mostly prior to the formation of a hypercompact HII region.

15 pages, 4 figures; Accepted by A&A

References in corpus (3)

• The Large APEX Bolometer Camera LABOCA
• The Arecibo Methanol Maser Galactic Plane Survey--I: Data
• The Arecibo Methanol Maser Galactic Plane Survey - II: Statistical and Multi-wavelength Counterpart Analysis

Cited by in corpus (12)

• ATLASGAL --- Environments of 6.7\,GHz methanol masers
• Confirmation of the exclusive association between 6.7-GHz methanol masers and high-mass star formation regions
• The Arecibo Methanol Maser Galactic Plane Survey-IV: Accurate Astrometry and Source Morphologies
• Discovery of the first methanol (CH3OH) maser in the Andromeda galaxy (M31)
• Simultaneous observation of water and class I methanol masers toward class II methanol maser sources
• A global view on star formation: The GLOSTAR Galactic plane survey III. 6.7 GHz methanol maser survey in Cygnus X
• EVN observations of 6.7 GHz methanol masers in clusters of massive young stellar objects
• Searching for new hypercompact HII regions
• The mid-infrared environments of 6.7 GHz Methanol Masers from the Methanol Multi-Beam Survey
• The first high-resolution observations of 19.9-GHz methanol masers
• Probing the early phases of high mass star formation with 6.7 GHz methanol masers
• Chemical environments of 6.7 GHz methanol maser sources