Discovery of molecular hydrogen line emission associated with methanol maser emission

We report the discovery of H2 line emission associated with 6.67-GHz methanol maser emission in massive star-forming regions. In our UNSWIRF/AATobservations, H2 1–0 S(1) line emission was found associated with an ultracompact H II region IRAS 14567–5846 and isolated methanol maser sites in G318:95–0:20, IRAS 15278–5620 and IRAS 16076–5134. Owing to the lack of radio continuum in the latter three sources, we argue that their H2 emission is shock excited, while it is UV-fluorescently excited in IRAS 14567–5846. Within the positional uncertainties of 3arcsec, the maser sites correspond to the location of infrared sources. We suggest that 6.67-GHz methanol maser emission is associated with hot molecular cores, and propose an evolutionary sequence of events for the process of massive star formation.