2017ApJ...836...59C

We explored the implication of the association (or lack of it) of 6.7 GHz class II methanol (CH₃OH) masers with massive dense cores (MDCs) detected (within a sample of ATLASGAL selected infrared quiet massive clumps) at 0.9 mm with Atacama Large Millimeter/submillimeter array. We found 42 out of the 112 cores (37.5%) detected with the Atacama Compact Array (ACA) to be associated with 6.7 GHz CH₃OH masers. The lowest mass core with CH₃OH maser association is ∼12 M_☉. The angular offsets of the ACA cores from the 6.7 GHz CH₃OH maser peak positions range from 0.''17 to 4.''79, with a median value of 2.''19. We found a weak correlation between the 0.9 mm continuum (MDCs) peak fluxes and the peak fluxes of their associated methanol multibeam (MMB) 6.7 GHz CH₃OH masers. About 90% of the cores associated with 6.7 GHz CH₃OH masers have masses of >40 M_☉. The CH₃OH maser containing cores are candidates for embedded high-mass protostellar objects in their earliest evolutionary stages. With our ACA 0.9 continuum data compared with the MMB 6.7 GHz CH₃OH maser survey, we have constrained the cores already housing massive protostars based on their association with the radiatively pumped 6.7 GHz CH₃OH masers.