J/A+A/658/A103 History independent tracers (Holdship+, 2022)
History independent tracers. Forgetful molecular probes of the physical
conditions of the dense interstellar medium.
Holdship J., Viti S.
<Astron. Astrophys. 658, A103 (2022)>
=2022A&A...658A.103H 2022A&A...658A.103H (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Molecular data
Keywords: methods: statistical - ISM: molecules - astrochemistry -
astronomical databases: miscellaneous - submillimeter: ISM -
ISM: general
Abstract:
Molecular line emission is a powerful probe of the physical conditions
of astrophysical objects but can be complex to model and it is often
unclear which transitions would be the best targets for observers who
wish to constrain a given parameter.
We produce a list of molecular species for which the gas history can
be ignored, removing a major modelling complexity. We then determine
the best of these species to observe in order to constrain various
physical parameters.
We use a large set of chemical models with different chemical
histories to determine which species have abundances at 1 MYr which
are insensitive to the initial conditions. We then use radiative
transfer modelling to produce the intensity of every transition of
these molecules. We finally compute the mutual information between the
physical parameters and all transitions and transition ratios in order
to rank their usefulness in determining the value of a given
parameter.
We find 48 species which are insensitive to the chemical history of
the gas, 23 of which have collisional data available. We produce a
ranked list of all transitions and ratios of these species by their
mutual information with various gas properties. We show mutual
information is an adequate measure of how well a transition can
constrain a physical parameter by recovering known probes and
demonstrating random forest regression models become more accurate
predictors when high scoring features are included. Therefore, this
list can be used to select target transitions for observations in
order to maximise knowledge about those physical parameters.
Description:
Mutual information scores between molecular lines or line ratios and
physical parameters. Calculated using line intensities from RADEX
calculations assuming a H2 ortho:para ratio of 3:1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
filters.dat 98 60830 Table of mutual information scores
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Byte-by-byte Description of file: filters.dat
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Bytes Format Units Label Explanations
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1- 24 A24 --- Feature Name of feature combining species and
transition frequency
26- 36 A11 --- Target Name of physical parameter for which mutual
information was calculated (1)
38- 55 F18.16 --- MutualInfo Mutual information score between the feature
and the target
57- 61 A5 --- Ratio [True /False] Flag for whether the feature
is a transition ratio
63- 67 A5 --- Mol1 Molecule to which the first (or only for
non-ratios) transition belongs
69- 73 A5 --- Mol2 Molecule to which the second transition
belongs for ratios otherwise None
75- 84 A10 --- Mols Combined list of molecules (Mol1-Mol2)
86- 91 F6.2 GHz Freq1 Rest frequency of first transition
93- 98 F6.2 GHz Freq2 Rest frequency of second transition
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Note (1): Physical parameter are Av, initialDens, initialTemp, radfield, rout
and zeta.
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Acknowledgements:
Jonathan Holdship, holdship(at)strw.leidenuniv.nl
(End) Patricia Vannier [CDS] 17-Dec-2021