Class II 6.7 GHz Methanol Maser Association with Young Massive Cores Revealed by ALMA.

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 . 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. [ABSTRACT FROM AUTHOR]