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

Abstract

Context. Acetone (CH_{3COCH3) is a carbonyl-bearing complex organic molecule, yet interstellar observations of acetone remain limited. Studying the formation and distribution of CH3COCH3 in the interstellar medium can provide valuable insights into prebiotic chemistry and the evolution of interstellar molecules.Aims. We explore the spatial distribution of CH3COCH3 and its correlation with the O-bearing molecules acetaldehyde (CH3CHO) and methanol (CH3OH), as well as the N-bearing molecule ethyl cyanide (C2H5CN), 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 CH3COCH3, CH3CHO, CH3OH, and C2H5CN and derived their rotation temperatures, column densities, and abundances under the assumption of local thermodynamic equilibrium.Results. CH3COCH3 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⊙). CH3CHO and CH3OH are also detected in all 16 cores, while C2H5CN is detected in 15. The integrated intensity maps reveal similar spatial distributions for CH3COCH3, CH3CHO, CH3OH, and C2H5CN. The line emission peaks of all four molecules coincide with the continuum emission peaks in regions without ultra-compact HII 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 CH3COCH3, CH3CHO, and CH3OH originate from the same gas. The observed temperatures and abundances of CH3COCH3 are consistent with model predictions involving grain surface chemistry.}