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

The association of 6.7 GHz class II methanol (CH₃OH) masers with ATLASGAL/ ALMA 0.9 mm massive dense cores is presented in this work from a statistical viewpoint. 42 of the 112 cores (37.5%) detected with the Atacama Compact Array (ACA) excite 6.7 GHz CH₃OH masers. ACA cores have offsets 0\rlap.''17 to 4\rlap.''79 from the methanol multibeam survey (MMB), with a median of 2.''19. Approximately 90% of the MMB-associated cores are of masses > 40 M_⊙. Because all the cores show evidence of outflow activity, and only a fraction of the cores excited CH₃OH masers, we suggest that outflows precede the emergence of maser emission. This first ALMA survey of massive dense cores combined with the MMB survey along with other maser specie surveys is a promising tool to trace the evolutionary sequence of high-mass stars.