Ice mantles on dust grains: dramatic variation of thickness with grain size

Abstract

We compute the desorption rate of icy mantles on dust grains as a function of the size and composition of both the grain and the mantle. We combine existing models of cosmic ray (CR) related desorption phenomena with a model of CR transport to accurately calculate the desorption rates in dark regions of molecular clouds. We show that different desorption mechanisms dominate for grains of different sizes, and in different regions of the cloud. We then use these calculations to investigate a simple model of the growth of mantles, given a distribution of grain sizes. We find that modest variations of the desorption rate with grain size lead to a strong dependence of mantle thickness on grain size. Furthermore, we show that freeze-out is almost complete in the absence of an external UV field, even when photodesorption from CR produced UV is taken into consideration. Even at gas densities of $10^4$ $\mathrm{c}{\mathrm{m}}^{-3}$, less than 30\% of the CO remains in the gas phase after $3\times 10^5$ years for standard values of the CR ionization rate.

arXiv commentAccepted to MNRAS

References in corpus (51)

• Dust Grain Size Distributions and Extinction in the Milky Way, LMC, and SMC
• Observations of the Icy Universe
• Infrared Emission from Interstellar Dust. I. Stochastic Heating of Small Grains
• A three-phase chemical model of hot cores: the formation of glycine
• Scattering by Interstellar Dust Grains. II. X-Rays
• Tracing the Mass during Low-Mass Star Formation. II. Modelling the Submillimeter Emission from Pre-Protostellar Cores
• Water, O2 and Ice in Molecular Clouds
• N2H+ and C18O Depletion in a Cold Dark Cloud
• Investigating the Cosmic-Ray Ionization Rate in the Galactic Diffuse Interstellar Medium through Observations of H3+
• Gas and grain chemical composition in cold cores as predicted by the Nautilus 3-phase model
• Thermal Desorption of Water-Ice in the Interstellar Medium
• Photodesorption of Ices II: H2O and D2O
• Observing the gas temperature drop in the high-density nucleus of L 1544
• On the Formation of CO2 and Other Interstellar Ices
• Dust coagulation and fragmentation in molecular clouds. I. How collisions between dust aggregates alter the dust size distribution
• Interstellar Carbon in Translucent Sightlines
• Formation of Complex Molecules in Prestellar Cores: a Multilayer Approach
• Coulomb Explosion and Thermal Spikes
• First detection of water vapor in a pre-stellar core
• A census of dense cores in the Aquila cloud complex: SPIRE/PACS observations from the Herschel Gould Belt survey
• Cosmic-ray ionisation in circumstellar discs
• Dynamics and Depletion in Thermally Supercritical Starless Cores
• The dust temperature distribution in prestellar cores
• CO ice photodesorption: A wavelength-dependent study
• UV photodesorption of methanol in pure and CO-rich ices: desorption rates of the intact molecule and of the photofragments
• Desorption of CO and O2 interstellar ice analogs
• Vacuum-UV spectroscopy of interstellar ice analogs. I. Absorption cross-sections of polar-ice molecules
• Decoupling of Magnetic Fields in Collapsing Protostellar Envelopes and Disk Formation and Fragmentation
• On Cosmic Ray-Driven Grain Chemistry in Cold Core Models
• Composition of Primary Cosmic-Ray Nuclei at High Energies
• Efficient Production of S${}_8$ in Interstellar Ices: The effects of cosmic ray-driven radiation chemistry and non-diffusive bulk reactions
• High sensitivity maps of molecular ions in L1544: I. Deuteration of N2H+ and HCO+ and first evidence of N2D+ depletion
• Impulsive Spot Heating and Thermal Explosion of Interstellar Grains Revisited
• Efficiency of non-thermal desorptions in cold-core conditions. Testing the sputtering of grain mantles induced by cosmic rays
• Parameterizing the interstellar dust temperature
• Vacuum-UV spectroscopy of interstellar ice analogs. II. Absorption cross-sections of nonpolar ice molecules
• Effect of Grain Size on Differential Desorption of Volatile Species and on Non-ideal MHD Diffusivity
• Penetration of cosmic rays into dense molecular clouds: role of diffuse envelope
• Dust coagulation feedback on magnetohydrodynamic resistivities in protostellar collapse
• On Simulating the Proton-Irradiation of O${}_2$ and H${}_2$O Ices Using Astrochemical-type Models, with Implications for Bulk Reactivity
• Cosmic ray sputtering yield of interstellar H2O ice mantles : Ice mantle thickness dependence
• Hydrodynamics with gas-grain chemistry and radiative transfer: comparing dynamical and static models
• Episodic Explosions in Interstellar Ices
• Rapid Elimination of Small Dust Grains in Molecular Clouds
• Magnetic Mirroring and Focusing of Cosmic Rays
• Monte Carlo radiative transfer in molecular cloud cores
• The effect of selective desorption mechanisms during interstellar ice formation
• Effect of grain size distribution and size-dependent grain heating on molecular abundances in starless and pre-stellar cores
• Cosmic ray sputtering yield of interstellar ice mantles: CO and CO2 ice thickness dependence
• Cosmic ray tracks in astrophysical ices: Modeling with the Geant4-DNA Monte Carlo Toolkit
• Connecting planet formation and astrochemistry: C/O and N/O of warm giant planets and Jupiter-analogs

Cited by in corpus (6)

• Icy molecule desorption in interstellar grain collisions
• The Effects of Cosmic Rays on the Chemistry of Dense Cores
• Towards a better understanding of ice mantle desorption by cosmic rays
• A multigrain-multilayer astrochemical model with variable desorption energy for surface species
• The Cosmic-Ray Induced Sputtering Process On Icy Grains
• The cosmic journey of dust grains -- from nucleation to planetary system