Towards a better understanding of ice mantle desorption by cosmic rays
arXiv:2207.14005 · doi:10.1093/mnras/stac2154
Abstract
The standard model of cosmic ray heating-induced desorption of interstellar ices is based on a continuous representation of the sporadic desorption of ice mantle components from classical (0.1 micron) dust grains. This has been re-evaluated and developed to include tracking the desorption through (extended) grain cooling profiles, consideration of grain size-dependencies and constraints to the efficiencies. A model was then constructed to study the true, sporadic, nature of the process with possible allowances from species co-desorption and whole mantle desorption from very small grains. The key results from the study are that the desorption rates are highly uncertain, but almost certainly significantly larger than have been previously determined. For typical interstellar grain size distributions it is found that the desorption is dominated by the contributions from the smallest grains. The sporadic desorption model shows that, if the interval between cosmic ray impacts is comparable to, or less than, the freeze-out timescale, the continuous representation is inapplicable; chemical changes may occur on very long timescales, resulting in strong gas phase chemical enrichments that have very non-linear dependences on the cosmic ray flux. The inclusion of even limited levels of species co-desorption and/or the contribution from very small grains further enhances the rates, especially for species such as H2O. In general we find that cosmic-ray heating is the dominant desorption mechanism in dark environments. These results may have important chemical implications for protostellar and protoplanetary environments.
19 pages with 3 figures, MNRAS accepted 28 July 2022
References in corpus (11)
- Water in star-forming regions (WISH): Physics and chemistry from clouds to disks as probed by Herschel spectroscopy
- Desorption From Interstellar Ices
- Impulsive Spot Heating and Thermal Explosion of Interstellar Grains Revisited
- A Revised Description of the Cosmic Ray-Induced Desorption of Interstellar Ices
- Effect of grain size distribution and size-dependent grain heating on molecular abundances in starless and pre-stellar cores
- The connection between warm carbon chain chemistry and interstellar irradiation of star-forming cores
- Chemical significance of different temperature regimes for cosmic-ray-induced heating of whole interstellar grains
- Ice mantles on dust grains: dramatic variation of thickness with grain size
- Evaporative cooling of icy interstellar grains II. Key parameters
- Evaporative cooling of icy interstellar grains. I. Basic characterization
- Water Ice Deposition and Growth in Molecular Clouds