D Navarro-Almaida1, R Le Gal2, A Fuente1, P Rivière-Marichalar1, V Wakelam3, S Cazaux4, P Caselli5, Jacob C Laas5, T Alonso-Albi1, J C Loison6, M Gerin7, C Kramer8, E Roueff9, R Bachiller1, B Commerçon10, R Friesen11, S García-Burillo1, J R Goicoechea12, B M Giuliano5, I Jiménez-Serra13, J M Kirk14, V Lattanzi5, J Malinen15,16, N Marcelino12, R Martín-Domènech2, G M Muñoz Caro13, J Pineda5, B Tercero1, S P Treviño-Morales17, O Roncero12, A Hacar18, M Tafalla1, D Ward-Thompson14. 1. Observatorio Astronómico Nacional (OAN), Alfonso XII, 3, 28014, Madrid, Spain. 2. Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA. 3. Laboratoire d'Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France. 4. Faculty of Aerospace Engineering, Delft University of Technology, Delft, The Netherlands; University of Leiden, P.O. Box 9513, NL, 2300 RA, Leiden, The Netherlands. 5. Centre for Astrochemical Studies, Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748, Garching, Germany. 6. Institut des Sciences Moléculaires (ISM), CNRS, Univ. Bordeaux, 351 cours de la Libération, F-33400, Talence, France. 7. Observatoire de Paris, PSL Research University, CNRS, École Normale Supérieure, Sorbonne Universités, UPMC Univ. Paris 06, 75005, Paris, France. 8. Instituto Radioastronomía Milimétrica (IRAM), Av. Divina Pastora 7, Nucleo Central, 18012, Granada, Spain. 9. Sorbonne Université, Observatoire de Paris, Université PSL, CNRS, LERMA, F-92190, Meudon, France. 10. École Normale Supérieure de Lyon, CRAL, UMR CNRS 5574, Université Lyon I, 46 Allée d'Italie, 69364, Lyon Cedex 07, France. 11. National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville VA USA 22901. 12. Instituto de Física Fundamental (CSIC), Calle Serrano 123, 28006, Madrid, Spain. 13. Centro de Astrobiología (CSIC-INTA), Ctra. de Ajalvir, km 4, Torrejón de Ardoz, 28850, Madrid, Spain. 14. Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK. 15. Department of Physics, University of Helsinki, PO Box 64, 00014, Helsinki, Finland. 16. Institute of Physics I, University of Cologne, Cologne, Germany. 17. Chalmers University of Technology, Department of Space, Earth and Environment, SE-412 93 Gothenburg, Sweden. 18. Leiden Observatory, Leiden University, PO Box 9513, 2300-RA, Leiden, The Netherlands.
Abstract
CONTEXT: Sulphur is one of the most abundant elements in the Universe. Surprisingly, sulphuretted molecules are not as abundant as expected in the interstellar medium and the identity of the main sulphur reservoir is still an open question. AIMS: Our goal is to investigate the H2S chemistry in dark clouds, as this stable molecule is a potential sulphur reservoir. METHODS: Using millimeter observations of CS, SO, H2S, and their isotopologues, we determine the physical conditions and H2S abundances along the cores TMC 1-C, TMC 1-CP, and Barnard 1b. The gas-grain model Nautilus is used to model the sulphur chemistry and explore the impact of photo-desorption and chemical desorption on the H2S abundance. RESULTS: Our modeling shows that chemical desorption is the main source of gas-phase H2S in dark cores. The measured H2S abundance can only be fitted if we assume that the chemical desorption rate decreases by more than a factor of 10 when n H > 2 × 104. This change in the desorption rate is consistent with the formation of thick H2O and CO ice mantles on grain surfaces. The observed SO and H2S abundances are in good agreement with our predictions adopting an undepleted value of the sulphur abundance. However, the CS abundance is overestimated by a factor of 5 - 10. Along the three cores, atomic S is predicted to be the main sulphur reservoir. CONCLUSIONS: The gaseous H2S abundance is well reproduced, assuming undepleted sulphur abundance and chemical desorption as the main source of H2S. The behavior of the observed H2S abundance suggests a changing desorption efficiency, which would probe the snowline in these cold cores. Our model, however, highly overestimates the observed gas-phase CS abundance. Given the uncertainty in the sulphur chemistry, we can only conclude that our data are consistent with a cosmic elemental S abundance with an uncertainty of a factor of 10.
CONTEXT: Sulphur is one of the most abundant elements in the Universe. Surprisingly, sulphuretted molecules are not as abundant as expected in the interstellar medium and the identity of the main sulphur reservoir is still an open question. AIMS: Our goal is to investigate the H2S chemistry in dark clouds, as this stable molecule is a potential sulphur reservoir. METHODS: Using millimeter observations of CS, SO, H2S, and their isotopologues, we determine the physical conditions and H2S abundances along the cores TMC 1-C, TMC 1-CP, and Barnard 1b. The gas-grain model Nautilus is used to model the sulphur chemistry and explore the impact of photo-desorption and chemical desorption on the H2S abundance. RESULTS: Our modeling shows that chemical desorption is the main source of gas-phase H2S in dark cores. The measured H2S abundance can only be fitted if we assume that the chemical desorption rate decreases by more than a factor of 10 when n H > 2 × 104. This change in the desorption rate is consistent with the formation of thick H2O and CO ice mantles on grain surfaces. The observed SO and H2S abundances are in good agreement with our predictions adopting an undepleted value of the sulphur abundance. However, the CS abundance is overestimated by a factor of 5 - 10. Along the three cores, atomic S is predicted to be the main sulphur reservoir. CONCLUSIONS: The gaseous H2S abundance is well reproduced, assuming undepleted sulphur abundance and chemical desorption as the main source of H2S. The behavior of the observed H2S abundance suggests a changing desorption efficiency, which would probe the snowline in these cold cores. Our model, however, highly overestimates the observed gas-phase CS abundance. Given the uncertainty in the sulphur chemistry, we can only conclude that our data are consistent with a cosmic elemental S abundance with an uncertainty of a factor of 10.
Authors: Jean-Christophe Loison; Valentine Wakelam; Pierre Gratier; Kevin M Hickson; Aurore Bacmann; Marcelino Agùndez; Nuria Marcelino; José Cernicharo; Viviana Guzman; Maryvonne Gerin; Javier R Goicoechea; Evelyne Roueff; Franck Le Petit; Jérome Pety; Asunción Fuente; Pablo Riviere-Marichalar Journal: Mon Not R Astron Soc Date: 2019-02-27 Impact factor: 5.287
Authors: Duncan V Mifsud; Péter Herczku; Richárd Rácz; K K Rahul; Sándor T S Kovács; Zoltán Juhász; Béla Sulik; Sándor Biri; Robert W McCullough; Zuzana Kaňuchová; Sergio Ioppolo; Perry A Hailey; Nigel J Mason Journal: Front Chem Date: 2022-09-26 Impact factor: 5.545