The GUAPOS project

VI. The chemical inventory of shocked gas

¹ Centro de Astrobiología (CAB), CSIC-INTA, Ctra. de Ajalvir, km. 4, Torrejón de Ardoz, 28850 Madrid, Spain
² Departamento de Física de la Tierra y Astrofísica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
³ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁴ Institut de Ciències de l’Espai (ICE, CSIC), Carrer de Can Magrans, s/n, 08193 Bellaterra, Barcelona, Spain
⁵ Institut d’Estudis Espacials de Catalunya (IEEC), Barcelona, Spain
⁶ INAF-IAPS, via del Fosso del Cavaliere 100, 00133 Roma, Italy
⁷ Leiden Observatory, Leiden University, Huygens Laboratory, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
⁸ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 12 August 2025
Accepted: 15 September 2025

Abstract

The study of the chemical composition of star-forming regions is key to understanding the chemical ingredients available during the formation of planetary systems. Because the chemical inventory of interstellar dust grains in the prestellar phases might be altered by protostellar warming, an alternative to inferring the chemical composition of the grains might be to observe regions that are affected by shocks associated with molecular outflows. These shocks are able to desorb the molecules and might produce less chemical processing because the timescales are shorter. We present a detailed study of the chemical reservoir of a shocked region located in the G31.41+0.31 protocluster using data from the G31.41+0.31 Unbiased ALMA sPectral Observational Survey (GUAPOS). We report the detection of 30 molecular species (plus 18 isotopologs) and derived the column densities. We compared the molecular ratios in the shocked region with those derived toward the hot core of G31.41+0.31. They are poorly correlated, with the exception of N-bearing species. Our results confirm observationally that a different level of chemical alteration is present in hot cores and in shocks. While the former likely alter the molecular ratios by thermal processing during longer timescales, the latter might represent freshly desorbed material that constitutes a better proxy of the composition of the ice mantle. The similarity of the molecular ratios of the N-bearing species in the G31.41+0.31 shock and the hot core suggests that these species are predominantly formed at early evolutionary stages. Interestingly, the abundances in the G31.41+0.31 shock are better correlated with other shock-dominated regions (two protostellar outflows and a molecular cloud in the Galactic center). This suggests that gas-phase chemistry after shock-induced ejection from grains is negligible and that the composition of the ice mantle is similar regardless of the Galactic environment.