ALMA observations of CH₃COCH₃ and the related species CH₃CHO, CH₃OH, and C₂H₅CN in line-rich molecular cores

Context . Acetone (CH 3 COCH 3 ) is a carbonyl-bearing complex organic molecule, yet interstellar observations of acetone remain limited. Studying the formation and distribution of CH 3 COCH 3 in the interstellar medium can provide valuable insights into prebiotic chemistry and the evolution of interstellar molecules. Aims . We explore the spatial distribution of CH 3 COCH 3 and its correlation with the O-bearing molecules acetaldehyde (CH 3 CHO) and methanol (CH 3 OH), as well as the N-bearing molecule ethyl cyanide (C 2 H 5 CN), in massive protostellar clumps. Methods . We observed 11 massive protostellar clumps using ALMA at 345 GHz, with an angular resolution of 0.7′′−1.0′′. Spectral line transitions were identified using the eXtended CASA Line Analysis Software Suite. We constructed integrated intensity maps of CH 3 COCH 3 , CH 3 CHO, CH 3 OH, and C 2 H 5 CN and derived their rotation temperatures, column densities, and abundances under the assumption of local thermodynamic equilibrium. Results . CH 3 COCH 3 is detected in 16 line-rich cores from 9 massive protostellar clumps: 12 high-mass cores (core mass >8 M ⊙ ), 3 intermediate-mass cores (2–8 M ⊙ ), and 1 low-mass core (<2 M ⊙ ). CH 3 CHO and CH 3 OH are also detected in all 16 cores, while C 2 H 5 CN is detected in 15. The integrated intensity maps reveal similar spatial distributions for CH 3 COCH 3 , CH 3 CHO, CH 3 OH, and C 2 H 5 CN. The line emission peaks of all four molecules coincide with the continuum emission peaks in regions without ultra-compact H II regions. Significant correlations are observed in the abundances of these molecules, which also exhibit similar average temperatures. Conclusions . Our observational results, supported by chemical models, suggest that CH 3 COCH 3 , CH 3 CHO, and CH 3 OH originate from the same gas. The observed temperatures and abundances of CH 3 COCH 3 are consistent with model predictions involving grain surface chemistry.