Abstract

The Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures (QUARKS) survey observed 139 infrared-bright (IR-bright) massive protoclusters at 1.3 mm wavelength with the Atacama Large Millimeter/submillimeter Array (ALMA). This study investigates clump-to-core fragmentation and searches for candidate high-mass starless cores within IR-bright clumps using combined ALMA 12 m (C-2) and Atacama Compact Array 7 m data, providing ?1? (?0.02 pc at 3.7 kpc) resolution and ?0.6 mJy beam?1 continuum sensitivity (?0.3 M? at 30 K). We identified 1562 compact cores from 1.3 mm continuum emission using getsf. Observed linear core separations (?obs) are significantly less than the thermal Jeans length (?J), with the ?obs/?J ratios peaking at ?0.2. This indicates that thermal Jeans fragmentation has taken place within the IR-bright protocluster clumps studied here. The observed low ratio of ?obs/?J ? 1 could be the result of evolving core separation or hierarchical fragmentation. Based on associated signatures of star formation (e.g., outflows and ionized gas), we classified cores into three categories: 127 starless, 971 warm, and 464 evolved cores. Two starless cores have masses exceeding 16 M?, and represent high-mass candidates. The scarcity of such candidates suggests that competitive accretion-type models could be more applicable than turbulent core accretion-type models in high-mass star formation within these IR-bright protocluster clumps. © 2025. The Author(s). Published by the American Astronomical Society.