J/A+A/607/A118 Models for molecular transitions (Viti, 2017)
Molecular transitions as probes of the physical conditions of extragalactic
environments.
Viti S.
<Astron. Astrophys. 607, A118 (2017)>
=2017A&A...607A.118V 2017A&A...607A.118V (SIMBAD/NED BibCode)
ADC_Keywords: Models ; Molecular clouds ; Abundances
Keywords: galaxies: active - astrochemistry - molecular processes -
radiative transfer
Abstract:
We present a method to interpret molecular observations and molecular
line ratios in nearby extragalactic regions.
Ab initio grids of time dependent chemical models, varying in gas
density, temperature, cosmic ray ionization rate, and radiation field,
are used as input to RADEX calculations. Tables of abundances, column
densities, theoretical line intensities, and line ratios for some of
the most used dense gas tracers are provided. The degree of
correlation as well as degeneracy inherent in molecular ratios is
discussed. Comparisons of the theoretical intensities with example
observations are also provided.
We find that, within the parameters space explored, chemical
abundances can be constrained by a well defined set of gas density-gas
temperature-cosmic ray ionization rate for the species we investigate
here. However, line intensities, as well as, more importantly, line
ratios, from different chemical models can be very similar leading to
a clear degeneracy. We also find that the gas subjected to a galactic
cosmic ray ionization rate will not necessarily have reached steady
state by 1 million years. The species most affected by time dependency
effects are HCN and CS, both high density tracers. We use our ab
initio method to fit an example set of data from two galaxies (M82
and, NGC 253). We find that (i) molecular line ratios can be easily
matched even with erroneous individual line intensities; (ii) no set
of species can be matched by a one-component ISM; (iii) a species may
be a good tracer of an energetic process but only under specific
density and temperature conditions.
We provide tables of chemical abundances and line intensities ratios
for some of the most commonly observed extragalactic tracers of dense
gas for a grid of models. We show that by taking into consideration
the chemistry behind each species and the individual line intensities,
many degeneracies that arise by just using molecular line ratios can
be avoided. Finally we show that using a species or a ratio as a
tracer of an individual energetic process (e.g. cosmic rays, UV) ought
to be done with caution.
Description:
We present a grid of chemical models and provides the abundances, the
abundance ratios and column densities of the some of the most common
tracers for a large parameter space in gas density, temperature,
cosmic ray ionization rate, and radiation field (Tables 1-6). The
theoretical abundances are then used as inputs to a radiative transfer
code to derive the theoretical intensities for the parameter space
investigated by the chemical models (Tables 7, 8, 10-16).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 62 67 Grid of chemical models and molecular abundances
of selected species
tablea2.dat 94 67 Grid of chemical models, molecular column
densities and ratios of selected species
tablea3.dat 34 32 Column densities at 106yrs for Models showing
changes between 1 and 10 million years
tablea4.dat 26 67 Column densities at 107yrs for other
selected species
tablea5.dat 42 30 Column densities at 106yrs for other
selected species
table1.dat 43 3 CH3OH and HNCO column densities at two
different times 106yrs for shock models only
table2.dat 43 670 *Theoretical integrated line intensities for
final time step (107yrs)
table3.dat 43 310 *Theoretical integrated line intensities for
chemical models at 106 yrs
table4.dat 62 67 Theoretical HCN/HCO+ ratios
table5.dat 28 67 *SiO theoretical integrated line intensities for
chemical models at 107 yrs
table6.dat 28 31 *SiO theoretical integrated line intensities for
chemical models at 106yrs
table7.dat 40 67 *Selected SO theoretical integrated line intensities
for chemical models at 107 yrs
table8.dat 40 31 *Selected SO theoretical integrated line intensities,
for chemical models at 106yrs
table9.dat 28 67 *Selected HNC theoretical integrated line intensities
for chemical models at 107 yrs
table10.dat 28 31 *Selected HNC theoretical integrated line intensities,
for chemical models at 106yrs
table11.dat 48 30 *Selected HNCO theoretical integrated line intensities
for chemical models at 106yrs
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Note on table2.dat: The intensities were computed using the column densities,
temperatures and gas densities from the chemical models at the final time
step (107yrs) as input to RADEX. The models are for a linewidth of 100km/s.
Note on table3.dat: The intensities were computed using the column densities,
temperatures and gas densities from the chemical models at 106yrs, using a
linewidth of 100km/s.
Note on table5.dat, table7.dat table9.dat: computed using the column
densities, temperatures and gas densities from the chemical models at 107yrs,
using a linewidth of 100km/s.
Note on table6.dat table8.dat table10.dat table11.dat: computed using the
column densities, temperatures and gas densities from the chemical models
at 106yrs, using a linewidth of 100km/s.
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See also:
J/A+A/574/A127 : Photodissociation with mechanical heating (Kazandjian+, 2015)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- M [1/67] Model number
4- 9 I6 --- zeta [1-100000] Cosmic ray ionization rate
(1, 10, 500, 5000 or 100000) in standard
galactic cosmic ray ionization field zeta0
11- 13 I3 --- chi [1-500]? Radiation field (1, 10 or 500) in
Draine unit (1 Draine = 1.69G0, G0=1
corresponds to 1.2uW/m2)
15- 17 I3 K T [50-200]? Gas temperature (50, 100 or 200)
18- 22 A5 --- n_T [shock ] No temperature value at shock
24- 27 E4.1 cm-3 nH [1e+4/1e+6] Gas density
29- 30 I2 mag AV Initial visual extinction before the passage
of the shock
32- 38 E7.2 --- X(CO) CO abundance
40- 46 E7.2 --- X(HCO+) HCO+ abundance
48- 54 E7.2 --- X(HCN) HCN abundance
56- 62 E7.2 --- X(CS) CS abundance
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- M [1/67] Model number
4- 9 I6 --- zeta [1-100000]? Cosmic ray ionization rate
(1, 10, 500, 5000 or 100000) in standard
galactic cosmic ray ionization field zeta0
11- 13 I3 --- chi [1-500] Radiation field (1, 10 or 500) in
Draine unit (1 Draine = 1.69G0, G0=1
corresponds to 1.2uW/m2)
15- 17 I3 K T [50-200]? Gas temperature (50, 100 or 200)
18- 22 A5 --- n_T [shock ] No temperature value at shock
24- 27 E4.1 cm-3 nH [1e+4/1e+6] Gas density
29- 30 I2 mag AV Initial visual extinction before the passage
of the shock
32- 38 E7.2 cm-2 N(CO) CO column density
40- 46 E7.2 cm-2 N(HCO+) HCO+ column density
48- 54 E7.2 cm-2 N(HCN) HCN column density
56- 62 E7.2 cm-2 N(CS) CS column density
64- 70 E7.2 --- HCN/HCO+ HCN/HCO+ line ratio
72- 78 E7.2 --- HCN/CO HCN/CO line ratio
80- 86 E7.2 --- HCO+/CO HCO+/CO line ratio
88- 94 E7.2 --- CS/CO HS/CO line ratio
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Byte-by-byte Description of file: tablea3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- M [1/67] Model number
4- 10 E7.2 cm-2 N(CO) CO column density
12- 18 E7.2 cm-2 N(HCO+) HCO+ column density
20- 26 E7.2 cm-2 N(HCN) HCN column density
28- 34 E7.2 cm-2 N(CS) CS column density
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Byte-by-byte Description of file: tablea4.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- M [1/67] Model number
4- 10 E7.2 cm-2 N(SiO) SiO column density
12- 18 E7.2 cm-2 N(HNC) HNC column density
20- 26 E7.2 cm-2 N(SO) SO column density
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Byte-by-byte Description of file: tablea5.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- M [1/67] Model number
4- 10 E7.2 cm-2 N(CH3OH) CH3OH column density
12- 18 E7.2 cm-2 N(SiO) SiO column density
20- 26 E7.2 cm-2 N(HNC) HNC column density
28- 34 E7.2 cm-2 N(SO) SO column density
36- 42 E7.2 cm-2 N(HNCO) HNCO column density
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- M [1/67] Model number
4- 6 I3 yr TimeM Time when the temperature of the gas reaches
its maximum (1)
8- 14 E7.2 cm-2 N(CH3HO)M CH3OH column density at TimeM
16- 22 E7.2 cm-2 N(HNCO)M HNCO column density at TimeM
24- 27 E4.1 yr Time [1E+5] Second time
29- 35 E7.2 cm-2 N(CH3HO) CH3OH column density at Time
37- 43 E7.2 cm-2 N(HNCO) HNCO column density at Time
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Note (1): TimeM corresponds to a time when the temperature of the gas reaches
its maximum, which is different among models.
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Byte-by-byte Description of file: table2.dat table3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- M [1/67] Model number
4- 5 I2 --- Ju Upper level
7 I1 --- Jl Lower level
9- 16 E8.3 K.km/s I(CO) CO theoretical integrated line intensity
at (Ju, Jl) transition
18- 25 E8.3 K.km/s I(HCO+) HCO+ theoretical integrated line intensity
at (Ju, Jl) transition
27- 34 E8.3 K.km/s I(HCN) ?=- HCN theoretical integrated line intensity
at (Ju, Jl) transition
36- 43 E8.3 K.km/s I(CS) CS theoretical integrated line intensity
at (Ju, Jl) transition
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- M [1/67] Model number
4- 8 E5.1 --- R10 ?=- HCN/HCO+ line ratio for transition (1, 0)
10- 14 E5.1 --- R21 HCN/HCO+ line ratio for transition (2,1)
16- 20 E5.1 --- R32 ?=- HCN/HCO+ line ratio for transition (3, 2)
22- 26 E5.1 --- R43 ?=- HCN/HCO+ line ratio for transition (4, 3)
28- 32 E5.1 --- R54 ?=- HCN/HCO+ line ratio for transition (5, 4)
34- 38 E5.1 --- R65 HCN/HCO+ line ratio for transition (6, 5)
40- 44 E5.1 --- R76 HCN/HCO+ line ratio for transition (7, 6)
46- 50 E5.1 --- R87 HCN/HCO+ line ratio for transition (8, 7)
52- 56 E5.1 --- R98 HCN/HCO+ line ratio for transition (9, 8)
58- 62 E5.1 --- R109 HCN/HCO+ line ratio for transition (10, 9)
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Byte-by-byte Description of file: table5.dat table6.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- M [1/67] Model number
4 I1 --- Ju1 Upper level
6 I1 --- Jl1 Lower level
8- 15 E8.3 K.km/s I(SiO)1 Theoretical SiO integrated line intensity
for Ju1, Jl1 transition
17 I1 --- Ju2 Upper level
19 I1 --- Jl2 Lower level
21- 28 E8.3 K.km/s I(SiO)2 Theoretical SiO integrated line intensity for
Ju2, Jl2 transition
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Byte-by-byte Description of file: table7.dat table8.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- M [1/67] Model number
4- 7 A4 --- Ju1 Upper level
9- 12 A4 --- Jl1 Lower level
14- 21 E8.3 K.km/s I(SO)1 ?=- Theoretical SO integrated line intensity
for Ju1, Jl1 transition
23- 26 A4 --- Ju2 Upper level
28- 31 A4 --- Jl2 Lower level
33- 40 E8.3 K.km/s I(SO)2 ?=- Theoretical SO integrated line intensity
for Ju2, Jl2 transition
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Byte-by-byte Description of file: table9.dat table10.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- M [1/67] Model number
4 I1 --- Ju1 Upper level
6 I1 --- Jl1 Lower level
8- 15 E8.3 K.km/s I(HNC)1 Theoretical HNC integrated line intensity
for Ju1, Jl1 transition
17 I1 --- Ju2 Upper level
19 I1 --- Jl2 Lower level
21- 28 E8.3 K.km/s I(HNC)2 Theoretical HNC integrated line intensity
for Ju2, Jl2 transition
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Byte-by-byte Description of file: table11.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- M [1/67] Model number
4- 9 A6 --- Ju1 Upper level
11- 16 A6 --- Jl1 Lower level
18- 25 E8.3 K.km/s I(HNCO)1 ?=- Theoretical HNCO integrated line intensity
for Ju1, Jl1 transition
27- 32 A6 --- Ju2 Upper level
34- 39 A6 --- Jl2 Lower level
41- 48 E8.3 K.km/s I(HNCO)2 ?=- Theoretical HNCO integrated line intensity
for Ju2, Jl2 transition
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Acknowledgements:
Serena Viti, sv(at)star.ucl.ac.uk
(End) Patricia Vannier [CDS] 06-Sep-2017