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

¹ School of Physics and Astronomy, Yunnan University, Kunming 650091, PR China
² Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
³ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi 831399, China
⁴ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, PR China
⁵ Department of Astronomy, School of Physics, Peking University, Beijing 100871, PR China
⁶ Center for Astrophysics, Guangzhou University, Guangzhou 510006, PR China
⁷ Institute of Astrophysics, School of Physics and Electronic Science, Chuxiong Normal University, Chuxiong 675000, PR China
⁸ I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
⁹ Research Center for Intelligent Computing Platforms, Zhejiang Laboratory, Hangzhou 311100, PR China

^★ Corresponding authors; lichuanshou2021@163.com; qin@ynu.edu.cn; liutie@shao.ac.cn

Received: 30 October 2024
Accepted: 25 February 2025

Abstract

Context. Acetone (CH₃COCH₃) 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.