J/A+A/624/A108 Modeling interstellar sulfur depletion (Laas+, 2019)
Modeling sulfur depletion in interstellar clouds.
Laas J.C., Caselli P.
<Astron. Astrophys. 624, A108 (2019)>
=2019A&A...624A.108L 2019A&A...624A.108L (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Models
Keywords: astrochemistry - molecular processes - ISM: molecules
Abstract:
The elemental depletion of interstellar sulfur from the gas phase has
been a recurring challenge for astrochemical models. Observations show
that sulfur remains relatively non-depleted with respect to its cosmic
value throughout the diffuse and translucent stages of an interstellar
molecular cloud, but its atomic and molecular gas-phase constituents
cannot account for this cosmic value toward lines of sight containing
higher-density environments.
We have attempted to address this issue by modeling the evolution of
an interstellar cloud from its pristine state as a diffuse atomic
cloud to a molecular environment of much higher density, using a
gas-grain astrochemical code and an enhanced sulfur reaction network.
A common gas-grain astrochemical reaction network has been
systematically updated and greatly extended based on previous
literature and previous sulfur models, with a focus on the grain
chemistry and processes. A simple astrochemical model was used to
benchmark the resulting network updates, and the results of the model
were compared to typical astronomical observations sourced from the
literature.
Our new gas-grain astrochemical model is able to reproduce the
elemental depletion of sulfur, whereby sulfur can be depleted from the
gas-phase by two orders of magnitude, and that this process may occur
under dark cloud conditions if the cloud has a chemical age of at
least 106 years. The resulting mix of sulfur-bearing species on the
grain ranges across all the most common chemical elements (H/C/N/O),
not dissimilar to the molecules observed in cometary environments.
Notably, this mixture is not dominated simply by H2S, unlike all other
current astrochemical models.
Despite our relatively simple physical model, most of the known
gas-phase S-bearing molecular abundances are accurately reproduced
under dense conditions, however they are not expected to be the
primary molecular sinks of sulfur. Our model predicts that most of the
"missing" sulfur is in the form of organo-sulfur species that are
trapped on grains.
Description:
We have used an updated gas/grain astrochemical model to study the
elemental depletion of interstellar sulfur within an evolving
molecular cloud. The updates to the underlying chemical model includes
updates to both the thermochemistry of all grain surface species, as
well as revised data of previously-considered chemical
processes/reactions and new reactions based on recent laboratory and
theoretical studies. We provide here in these CDS tables the full
tables associated with Table A.1 and Table B.4 from the manuscript.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 59 288 Thermochemistry for all grain species
tableb4.dat 145 635 New sulfur reactions
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Name Grain surface molecular species
16- 20 I5 K Ebind Grain surface binding energy
24- 30 F7.2 kcal/mol delH_f ? Heat of formation
35- 59 A25 --- Remarks Remark/reference about tabulated values (1)
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Note (1): We include here either the literature reference to an updated value or
the explicit formula based on the additive property derived from other
species. In cases of no references/remarks, it is implied that the value
remains the same as the previous OSU model, presented in Garrod et al.
(2008ApJ...682..283G 2008ApJ...682..283G).
References as follows:
1 = Schuurman et al. (2004JChPh.12011586S 2004JChPh.12011586S)
2 = He et al. (2014PCCP...16.3493H 2014PCCP...16.3493H)
3 = Wakelam et al. (2017MolAs...6...22W 2017MolAs...6...22W)
4 = Martin-Domenech et al. (2014A&A...564A...8M 2014A&A...564A...8M)
5 = Jing et al. (2012ApJ...756...98J 2012ApJ...756...98J)
6 = Etim et al. (2016EPJP..131..448E 2016EPJP..131..448E)
7 = Riley et al. (2007JPCA..111.6044R 2007JPCA..111.6044R)
8 = Pozzo et al. (2008PhRvB..77j4103P 2008PhRvB..77j4103P)
9 = Cioslowski et al. (2000JChPh.113.9377C 2000JChPh.113.9377C)
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19 = Benson (1978, DOI: 10.1021/cr60311a003)
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Byte-by-byte Description of file: tableb4.dat
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Bytes Format Units Label Explanations
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1- 50 A50 --- Reaction Full chemical reaction
56- 57 I2 --- rtype Reaction type (1)
66- 73 E8.3 --- alpha α reaction coefficient
81- 85 F5.2 --- beta β reaction coefficient
94-100 F7.2 --- gamma γ reaction coefficient
106-145 A40 --- Remarks Remark/reference about tabulated values (2)
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Note (1): The "rtype" of each reaction can be used to look up their respective
rate coefficient using the listing shown in Appendix B.1.
Note (2): The following 28 sources are referenced in the table:
1 = Isoniemi et al. (1999CPL...311...47I 1999CPL...311...47I)
2 = Jimenez-Escobar et al. (2012ApJ...751L..40J 2012ApJ...751L..40J)
3 = Vidal et al. (2017MNRAS.469..435V 2017MNRAS.469..435V)
4 = Savage et al. (2004ApJ...608L..73S 2004ApJ...608L..73S)
5 = Shannon et al. (2014, DOI: 10.1039/C4RA03036B)
6 = Loison et al. (2012MNRAS.421.1476L 2012MNRAS.421.1476L)
7 = Majumdar et al. (2016MNRAS.458.1859M 2016MNRAS.458.1859M)
8 = Atkinson et al. (2004ACP.....4.1461A 2004ACP.....4.1461A)
9 = Glarborg et al. (2014JPCA..118.6798G 2014JPCA..118.6798G)
10 = Sendt et al. (2002, DOI: 10.1016/S1540-7489(02)80297-8)
11 = Andreazza et al. (2005ApJ...624.1121A 2005ApJ...624.1121A)
12 = Montaigne et al. (2005ApJ...631..653M 2005ApJ...631..653M)
13 = Heays et al. (2017A&A...602A.105H 2017A&A...602A.105H)
14 = Garozzo et al. (2010A&A...509A..67G 2010A&A...509A..67G)
15 = Yamada et al. (2002A&A...395.1031Y 2002A&A...395.1031Y)
16 = Ferrante et al. (2008ApJ...684.1210F 2008ApJ...684.1210F)
17 = Zhou et al. (2013, DOI: 10.1016/j.proci.2012.05.083)
18 = Cheng et al. (1996, DOI: 10.1021/jp9604960)
19 = Zhou et al. (2009JPCA..113.8299Z 2009JPCA..113.8299Z)
20 = Jimenez-Escobar et al. (2014MNRAS.443..343J 2014MNRAS.443..343J)
21 = Moore et al. (2007Icar..189..409M 2007Icar..189..409M)
22 = Ballester et al. (2008, DOI: 10.1002/kin.20340)
23 = Glarborg et al. (2013, DOI: 10.1002/kin.20778)
24 = Steudel et al. (2003, DOI: 10.1007/b12110)
25 = Sheraton et al. (1981, DOI: 10.1139/v81-397)
26 = Cruz-Diaz et al. (2014A&A...562A.119C 2014A&A...562A.119C)
27 = Hollenbach et al. (2009ApJ...690.1497H 2009ApJ...690.1497H)
28 = Fuente et al. (2017, DOI: 10.3847/2041-8213/aaa01b)
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Acknowledgements:
Jacob Laas, jclaas(at)mpe.mpg.de
(End) Jacob Laas [MPE, Germany], Patricia Vannier [CDS] 11-Mar-2019