ATLASGAL -- physical parameters of dust clumps associated with 6.7 GHz
  methanol masers
  We have constructed the largest sample of dust-associated class II 6.7 GHz
methanol masers yet obtained. New measurements from the the Methanol MultiBeam
(MMB) Survey were combined with the 870 $\mu$m APEX Telescope Large Area Survey
of the Galaxy (ATLASGAL) and the 850 $\mu$m JCMT Plane Survey (JPS). Together
with two previous studies we have now identified the host clumps for 958
methanol masers across the Galactic Plane, covering approximately 99% of the
MMB catalogue and increasing the known sample of dust-associated masers by over
30%. We investigate correlations between the physical properties of the clumps
and masers using distances and luminosities drawn from the literature. Clumps
hosting methanol masers are significantly more compact and have higher volume
densities than the general population of clumps. We determine a minimum volume
density threshold of $n$(H$_2$) $\geq 10^4$ cm$^{-3}$ for the efficient
formation of intermediate- and high-mass stars. We find 6.7 GHz methanol masers
are associated with a distinct part of the evolutionary process ($L_{\rm
bol}$/$M_{\rm fwhm}$ ratios of between 10$^{0.6}$ and 10$^{2.2}$) and have well
defined turning on and termination points. We estimate the lower limit for the
mass of embedded objects to be $\geq$ 6 M$_{\odot}$ and the statistical
lifetime of the methanol maser stage to be $\sim$ 3.3$\times$10$^{4}$ yrs. This
suggests that methanol masers are indeed reliable tracers of high mass star
formation, and indicates that the evolutionary period traced by this marker is
relatively rapid.
