http://arxiv.org/abs/1907.00564
Using the 870 $\mu$m APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) and the 850 $\mu$m JCMT Plane Survey (JPS), we have associated 257 class II 6.7 GHz methanol masers from the Methanol MultiBeam (MMB) survey with 246 submillimetre continuum sources in the Galactic region 20$^{\circ}$ < $\ell$ < 60$^{\circ}$ and $|b|$ < 1.5$^{\circ}$; this corresponds to 97% of methanol masers in the region. We combine these with a sample of 700 methanol masers associated with dense clumps reported in two previous studies. In total, we have identified the host clumps for 958 methanol masers across the Galactic plane between the longitude range 186$^{\circ}$ $\leq \ell \leq$ 60$^{\circ}$ and $|b|$ < 2$^{\circ}$; this corresponds to approximately 99% of the MMB catalogue. This sample is over 30% larger than the most complete maser-dust association sample to date. We use distances and physical properties drawn from the literature to investigate the correlations between the maser and clump properties, and investigate how the phase in a clumps evolution in which it host maser emission fits into the current theory of massive star formation. 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, both of which are consistent with the results of previous work.
S. Billington, J. Urquhart, C. Konig, et. al.
Tue, 2 Jul 19
16/79
Comments: 21 pages, 23 figures, 6 tables