Southern class I methanol masers at 36 and 44 GHz
  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 HII regions, dark clouds, shocks traced by the 4.5-micron
emission and 8.0-micron filaments. More than 700 maser component features were
found at each of the two methanol transitions, but with only 23 per cent
recognisable at both transitions; the morphology of class I 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 blue-shifted 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 blue
shift asymmetry of -0.57 km/s (uncertainties are 0.06 and 0.07 km/s 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 for the 36- and 44-GHz masers, respectively.
