The ALMA-QUARKS Survey: Hot Molecular Cores Are a Long-standing Phenomenon in the Evolution of Massive Protostars

Abstract We present an analysis of the QUARKS survey sample, focusing on protoclusters where hot molecular cores (HMCs; traced by CH 3 CN (12–11)) and HC/UC H ii regions (traced by H30 α /H40 α ) coexist. Using the high-resolution, high-sensitivity 1.3 mm data from the QUARKS survey, we identify 125 hot molecular fragments (HMFs), which represent the substructures of HMCs at higher resolution. From line integrated intensity maps of CH 3 CN (12 3 –11 3 ) and H30 α , we resolve the spatial distribution of HMFs and HC/UC H ii regions. By combining with observations of 12 CO (2–1) outflows and 1.3 mm continuum, we classify HMFs into four types: HMFs associated with jetlike outflow, wide-angle outflow, and nondetectable outflow and shell-like HMFs near HC/UC H ii regions. This diversity possibly indicates that the hot core could be a polymorphic and long-standing phenomenon in the evolution of massive protostars. The separation between HMFs and H30 α /H40 α emission suggests that sequential high-mass star formation within young protoclusters is not likely related to feedback mechanisms.