ATLASGAL -- Relationship between dense star forming clumps and
  interstellar masers
  We have used catalogues from several Galactic plane surveys and dedicated
observations to investigate the relationship between various maser species and
Galactic star forming clumps, as identified by the ATLASGAL survey. The maser
transitions of interest are the 6.7 & 12.2 GHz methanol masers, 22.2 GHz water
masers, and the masers emitting in the four ground-state hyperfine structure
transitions of hydroxyl. We find clump association rates for the water,
hydroxyl and methanol masers to be 56, 39 and 82 per cent respectively, within
the Galactic longitude range of 60{\deg} > $l$ > -60{\deg}. We investigate the
differences in physical parameters between maser associated clumps and the full
ATLASGAL sample, and find that clumps coincident with maser emission are more
compact with increased densities and luminosities. However, we find the
physical conditions within the clumps are similar for the different maser
species. A volume density threshold of $n$(H$_{2}$) > 10$^{4.1}$ cm$^{-3}$ for
the 6.7 GHz methanol maser found in our previous study is shown to be
consistent across for all maser species investigated. We find limits that are
required for the production of maser emission to be 500 L$_{\odot}$ and 6
M$_{\odot}$ respectively. The evolutionary phase of maser associated clumps is
investigated using the L/M ratio of clumps coincident with maser emission, and
these have similar L/M ranges (~10$^{0.2}$ - 10$^{2.7}$
L$_{\odot}$/M$_{\odot}$) regardless of the associated transitions. This implies
that the conditions required for the production of maser emission only occur
during a relatively narrow period during a star's evolution. Lower limits of
the statistical lifetimes for each maser species are derived, ranging from ~0.4
- 2 x 10$^{4}$ yrs and are in good agreement with the "straw man" evolutionary
model previously presented.
