Nautilus multi-grain model: Importance of cosmic-ray-induced desorption in determining the chemical abundances in the ISM

Wasim Iqbal 1 Valentine Wakelam 1
1 AMOR 2018
LAB - Laboratoire d'Astrophysique de Bordeaux [Pessac]
Abstract : Species abundances in the interstellar medium (ISM) strongly depend on the chemistry occurring at the surfaces of the dust grains. To describe the complexity of the chemistry, various numerical models have been constructed. In most of these models, the grains are described by a single size of 0.1$\mu$m. We study the impact on the abundances of many species observed in the cold cores by considering several grain sizes in the Nautilus multi-grain model. We used grain sizes with radii in the range of $0.005\mu$m to $0.25\mu$m. We sampled this range in many bins. We used the previously published, MRN and WD grain size distributions to calculate the number density of grains in each bin. Other parameters such as the grain surface temperature or the cosmic-ray-induced desorption rates also vary with grain sizes. We present the abundances of various molecules in the gas phase and also on the dust surface at different time intervals during the simulation. We present a comparative study of results obtained using the single grain and the multi-grain models. We also compare our results with the observed abundances in TMC-1 and L134N clouds. We show that the grain size, the grain size dependent surface temperature and the peak surface temperature induced by cosmic ray collisions, play key roles in determining the ice and the gas phase abundances of various molecules. We also show that the differences between the MRN and the WD models are crucial for better fitting the observed abundances in different regions in the ISM. We show that the small grains play a very important role in the enrichment of the gas phase with the species which are mainly formed on the grain surface, as non-thermal desorption induced by collisions of cosmic ray particles is very efficient on the small grains.
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Astronomy and Astrophysics, EDP Sciences, 2018, accepted for publication in A&A 2018
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Contributeur : Marie-Paule Pomies <>
Soumis le : mercredi 7 mars 2018 - 08:22:40
Dernière modification le : mardi 29 mai 2018 - 12:51:09

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Wasim Iqbal, Valentine Wakelam. Nautilus multi-grain model: Importance of cosmic-ray-induced desorption in determining the chemical abundances in the ISM. Astronomy and Astrophysics, EDP Sciences, 2018, accepted for publication in A&A 2018. 〈hal-01725052〉

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