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