Probing the early phases of high mass star formation with 6.7 GHz
  methanol masers
  Methanol masers at 6.7 GHz are the brightest of class II methanol masers and
have been found exclusively towards massive star forming regions. These masers
can thus be used as a unique tool to probe the early phases of massive star
formation. We present here a study of the spectral energy distributions of 320
6.7 GHz methanol masers chosen from the MMB catalogue, which fall in the Hi-GAL
range ($|l| \le 60^{\circ}$, $|b| \le 1^{\circ}$). The spectral energy
distributions are constructed from $870 - 70~\mu$m using data from the ATLASGAL
and Hi-GAL surveys. The emission from cold dust is modelled by a single grey
body component fit. We estimate the clump properties such as mass, FIR
luminosity and column density using the best fit parameters of the SED fits.
Considering the Kauffman criteria for massive star formation, we find that all
but a few maser hosts have the potential to harbour at least one high mass
star. The physical properties of the methanol maser hosts are also discussed.
The evolutionary stages of 6.7 GHz maser sources, explored using the mass
luminosity diagram, suggests that they are predominantly associated with high
mass stars with the majority being in the accretion phase. However, we observe
a small number of sources that could possibly be related to intermediate or
low-mass stars.
