Class II (6.7 GHz and 12.2 GHz) methanol masers are widespread in the Galaxy, and more than 1000 sources have been detected to data. In addition, Class II methanol masers are unique observed toward high-mass star formation regions and can faithfully reflect the evolutionary phase of massive star formation. Hence, methanol masers have gained increasing importance. Researchers from Purple Mountain Observatory (PMO) and Max-Planck-Institut für Radioastronomie have undertaken multi-line mapping observations of various molecular lines, including the NH3(1,1), (2,2), (3,3), (4,4) and 12CO (1-0) transitions, towards a sample of 9 low-luminosity 6.7-GHz masers, and 12CO (1-0) observations towards a sample of 8 high-luminosity 6.7-GHz masers by using PMO 13.7 m telescope and Effelsberg 100 m telescope. Comparative analysis of the physical quantities reveals marked distinctions between the low-luminosity and high-luminosity groups: in general, cores associated with high-luminosity 6.7-GHz masers are larger and more massive than those traced by low-luminosity 6.7-GHz masers; regions traced by the high-luminosity masers have larger column densities but lower densities than those of the low-luminosity maser regions. This work will be published in the Astrophysical Journal (refer to http://arxiv.org/abs/1007.1854). |
