A Catalog of Methanol Masers in Massive Star-forming Regions. III. The Molecular Outflow Sample

TL;DR

This study surveys 69 star-forming regions for 44 GHz methanol masers, revealing their prevalence in evolved objects and their association with molecular outflows, suggesting diverse shock-tracing roles in star formation.

Contribution

It provides the first interferometric survey of methanol masers in a large sample, highlighting their distribution relative to outflows and evolutionary stages.

Findings

Higher detection rates in more evolved objects.

Masers often located at outflow interfaces or bases.

Narrower linewidths compared to previous studies.

Abstract

We present an interferometric survey of the 44 GHz class I methanol maser transition toward a sample of 69 sources consisting of High Mass Protostellar Object candidates and Ultracompact (UC) H II regions. We found a 38% detection rate (16 of 42) in the HMPO candidates and a 54% detection rate (13 of 24) for the regions with ionized gas. This result indicates that class I methanol maser emission is more common toward more evolved young stellar objects of our sample. Comparing with similar interferometric data sets, our observations show narrower linewidths, likely due to our higher spatial resolution. Based on a comparison between molecular outflow tracers and the maser positions, we find several cases where the masers appear to be located at the outflow interface with the surrounding core. Unlike previous surveys, we also find several cases where the masers appear to be located close to the base of the molecular outflow, although we can not discard projection effects. This and other surveys of class I methanol masers not only suggest that these masers may trace shocks at different stages, but may even trace shocks arising from a number of different phenomena occurring in star-forming regions: young/old outflows, cloud-cloud collisions, expanding H II regions, among others.