Modelling methanol and hydride formation in the JWST Ice Age era
Year: 2025
Type: article
Abstract: Context. Recent JWST observations have measured the ice chemical composition towards two highly extinguished background stars, NIR38 and J110621, in the Chamaeleon I molecular cloud. The observed excess of extinction on the long-wavelength side of the H 2 O ice band at 3 μm has been attributed to a mixture of CH 3 OH with ammonia hydrates NH 3 ·H 2 O), which suggests that CH 3 OH ice in this cloud could have formed in a water-rich environment with little CO depletion. Laboratory experiments and quantum chemical calculations suggest that CH 3 OH could form via the grain surface reactions CH 3 + OH and/or C + H 2 O in water-rich ices. However, no dedicated chemical modelling has been carried out thus far to test their efficiency. In addition, it remains unexplored how the efficiencies of the proposed mechanisms depend on the astrochemical code employed. Aims. We modelled the ice chemistry in the Chamaeleon I cloud to establish the dominant formation processes of CH 3 OH, CO, CO 2 , and of the hydrides CH 4 and NH 3 (in addition to H 2 O). By using a set of state-of-the-art astrochemical codes (MAGICKAL, MONACO, Nautilus, U CLCHEM , and KMC simulations), we can test the effects of the different code architectures (rate equation vs. stochastic codes) and of the assumed ice chemistry (diffusive vs. non-diffusive). Methods. We consider a grid of models with different gas densities, dust temperatures, visual extinctions, and cloud-collapse length scales. In addition to the successive hydrogenation of CO, the codes’ chemical networks have been augmented to include the alternative processes for CH 3 OH ice formation in water-rich environments (i.e. the reactions CH 3 + OH → CH 3 OH and C + H 2 O → H 2 CO). Results. Our models show that the JWST ice observations are better reproduced for gas densities ≥10 5 cm −3 and collapse timescales ≥10 5 yr. CH 3 OH ice formation occurs predominantly (>99%) via CO hydrogenation. The contribution of reactions CH 3 + OH and C + H 2 O is negligible. The CO 2 ice may form either via CO + OH or CO + O depending on the code. However, KMC simulations reveal that both mechanisms are efficient despite the low rate of the CO + O surface reaction. CH 4 is largely underproduced for all codes except for U CLCHEM , for which a higher amount of atomic C is available during the translucent cloud phase of the models. Large differences in the predicted abundances are found at very low dust temperatures (T dust <12 K) between diffusive and non-diffusive chemistry codes. This is due to the fact that non-diffusive chemistry takes over diffusive chemistry at such low T dust . This could explain the rather constant ice chemical composition found in Chamaeleon I and other dense cores despite the different visual extinctions probed.
Source: Astronomy and Astrophysics
Authors: Izaskun Jiménez-Serra, Andrés Megías, Joseph Salaris, Herma Cuppen, Angèle Taillard, Miwha Jin, Valentine Wakelam, Anton I. Vasyunin, Paola Caselli, Yvonne J. Pendleton, Emmanuel Dartois, Jennifer A. Noble, Serena Viti, Katerina Borshcheva, Robin T. Garrod, Thanja Lamberts, Helen Fraser, Gary Melnick, Melissa McClure, Will Rocha, Maria N. Drozdovskaya, Dariusz C. Lis
Institutions: Centro de Astrobiología, Radboud University Nijmegen, Goddard Space Flight Center, Catholic University of America, Centre National de la Recherche Scientifique, Laboratoire d'Astrophysique de Bordeaux, Ural Federal University, Max Planck Institute for Extraterrestrial Physics, University of Central Florida, Institut des Sciences Moléculaires d'Orsay, Aix-Marseille Université, Physique des interactions ioniques et moléculaires, Leiden University, University of Bonn, Leiden Observatory, University College London, Institute of Astronomy, University of Virginia, The Open University, Center for Astrophysics Harvard & Smithsonian, Physikalisch-Meteorologisches Observatorium Davos, Jet Propulsion Laboratory
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
SDG: Climate action
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Science Foundation, National Aeronautics and Space Administration, California Institute of Technology, Ministerio de Ciencia, Innovación y Universidades, European Commission, Centre National d’Etudes Spatiales, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, Centre National de la Recherche Scientifique, Holcim Stiftung zur Förderung der Wissenschaftlichen Fortbildung, Jet Propulsion Laboratory, HORIZON EUROPE Framework Programme, Science and Technology Facilities Council, European Regional Development Fund, Agencia Estatal de Investigación, Planetary Science Division, European Social Fund
Awards: G1105844351, G1175115578, Dynamical and chemical modeling of low-mass star-forming cores, G1507096846, G1622782223, G1743472294, G2048821276, G210041235, G2262748287, G2274405149, Astronomy at The Open University 2023-2026 (Consolidated Grant), G2469010403, G2601397997, G2650114919, G2676722403, G300979063, G3055077951, G3123695474, Dutch Astrochemistry in the era of JWST (DAN-III), G34346518, G3452655474, G3480869486, G3648211085, G3681454997, G3702198118, G4042783231, G410571670, G4212894969, G425668148, G434337789, G451917667, G4526231891, G491712853, G5080475149, G5180915604, G5195188938, G5404395142, G546199279, G5539308778, G5635532810, G5817380855, G5967599077, G6218905885, G624877701, G6344031981, G6445425049, G7084143925, G7097722406, Spotting Ice! (SPICE): infrared light-field tracking of icy particles, Light-Field Motion Tracking in Laboratory Studies of Planet Formation, G7805626310, G7863371703, G8118709007, G830101876, G8497050386, G8888022036, G929308097
OpenAlex ID: W4408098932