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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 (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:
FileName Lrecl Records Explanations
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
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.
See also: J/A+A/574/A127 : Photodissociation with mechanical heating (Kazandjian+, 2015) Byte-by-byte Description of file: tablea1.dat
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 --- 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
Byte-by-byte Description of file: tablea2.dat
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
Byte-by-byte Description of file: tablea3.dat
Bytes Format Units Label Explanations
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
Byte-by-byte Description of file: tablea4.dat
Bytes Format Units Label Explanations
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
Byte-by-byte Description of file: tablea5.dat
Bytes Format Units Label Explanations
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
Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
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
Note (1): TimeM corresponds to a time when the temperature of the gas reaches its maximum, which is different among models.
Byte-by-byte Description of file: table2.dat table3.dat
Bytes Format Units Label Explanations
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
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
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)
Byte-by-byte Description of file: table5.dat table6.dat
Bytes Format Units Label Explanations
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
Byte-by-byte Description of file: table7.dat table8.dat
Bytes Format Units Label Explanations
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
Byte-by-byte Description of file: table9.dat table10.dat
Bytes Format Units Label Explanations
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
Byte-by-byte Description of file: table11.dat
Bytes Format Units Label Explanations
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
Acknowledgements: Serena Viti, sv(at)star.ucl.ac.uk
(End) Patricia Vannier [CDS] 06-Sep-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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