A computer program for fast non-LTE analysis of interstellar line spectra With diagnostic plots to interpret observed line intensity ratios

By F. V. D. Tak, J. Black, F. Schoeier, D. Jansen, E. Dishoeck. 2007

1,163 citations recorded by the source corpus.

Abstract: The large quantity and high quality of modern radio and infrared line observations require efficient modeling techniques to infer physical and chemical parameters such as temperature, density, and molecular abundances. We present a computer program to calculate the intensities of atomic and molecular lines produced in a uniform medium, based on statistical equilibrium calculations involving collisional and radiative processes and including radiation from background sources. Optical depth effects are treated with an escape probability method. The program is available on the World Wide Web at http://www.sron.rug.nl/~vdtak/radex/index.shtml . The program makes use of molecular data files maintained in the Leiden Atomic and Molecular Database (LAMDA), which will continue to be improved and expanded. The performance of the program is compared with more approximate and with more sophisticated methods. An Appendix provides diagnostic plots to estimate physical parameters from line intensity ratios of commonly observed molecules. This program should form an important tool in analyzing observations from current and future radio and infrared telescopes. Note: Accepted by AA 18 A4 pages, 11 figures;

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/dfdbc3807d1130ea7f573eef3fbc21610e29d228

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In Astronomy and Astrophysics

1. M. Cappellari
2. Mark R. Krumholz
3. P. Hopkins
4. L. Hernquist
5. Ralf Klessen
6. T. Naab
7. N. Evans II
8. F. Walter

In Atmospheric Science

1. Ralf Klessen
2. S. Glover
3. P. Caselli
4. E. Bergin
5. M. Tafalla
6. E. Dishoeck
7. J. Jørgensen
8. Simon Bruderer

In Spectroscopy

1. P. Caselli
2. Ralf Klessen
3. Simon Bruderer
4. E. Bergin
5. Y. Shirley
6. E. Dishoeck
7. M. Heyer
8. S. Glover

Citations in the corpus

• A Herschel [C ii] Galactic plane survey - I. The global distribution of ISM gas components (2013, methodology): “Pineda et al. (2010a) used the RADEX (van der Tak et al. 2007) excitation/radiative transfer code to predict line intensities from a gas with conditions similar to those of mask CO1 in the envelope of the Taurus molecular cloud.”
• An ALMA study of the Orion Integral Filament: I. Evidence for narrow fibers in a massive cloud (2018, result): “We have compared our estimates with the radiative transfer predictions provided by RADEX (van der Tak et al. 2007).”
• The warm gas atmosphere of the HD 100546 disk seen by Herschel - Evidence of a gas-rich, carbon-poor atmosphere? (2012, methodology): “In this work, we employ an approximation similar to the escape probability method (e.g. van der Tak et al. 2007).”
• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers (2015, methodology): “We shall use the radiative transfer code RADEX (van der Tak et al. 2007) with the escape probability formalism for a static, uniform density sphere, with the CMB as the only background radiation field, and with H2 as the dominant collision partner for all calculations.”
• FILAMENTARY ACCRETION FLOWS IN THE EMBEDDED SERPENS SOUTH PROTOCLUSTER (2013, methodology): “We ran several simple tests with the online non-LTE radiative transfer calculator, Radex13 (Van der Tak et al 2007) to check that the fitted values are reasonable.”
• Modelling CO emission – I. CO as a column density tracer and the X factor in molecular clouds (2010, methodology): “(8) Other functional forms of the escape probability can be defined for different scenarios (e.g. slab or spherical symmetry, see van der Tak et al. 2007).”
• Molecular Clouds in the Milky Way (2015, methodology): “Using the RADEX code (van der Tak et al. 2007) with N CO/δv ∼ 1017 cm−2 (km s−1)−1, the VHRG gas requires temperatures in excess of 40 K and densities greater than 104–5 cm−3.”
• ON THE EFFECT OF THE COSMIC MICROWAVE BACKGROUND IN HIGH-REDSHIFT (SUB-)MILLIMETER OBSERVATIONS (2013, methodology): “Some general aspects of CO excitation Here we summarize some of the main aspects of CO excitation; more details can be found e.g. in Spitzer (1978) or van der Tak et al. (2007).”
• First detection of CO in a high-redshift damped Lyman-α system (2008, methodology): “We ran the statistical equilibrium radiative transfer code RADEX, available on line (van der Tak et al. 2007), and found that for the kinetic temperature, T = 105 K, derived from H2, the collisional contributions to T01 and T12 are ≤5% and ≤2% for nH2 ≤ 25 cm−3.”
• The multi-phase winds of Markarian 231: from the hot, nuclear, ultra-fast wind to the galaxy-scale, molecular outflow (2015, methodology): “Modeling with RADEX non-LTE radiative transport models (van der Tak et al. 2007) to reproduce flux of CO and HCN, suggests instead that H13CN(4 − 3) is optically thin.”
• Water in star-forming regions with Herschel (WISH). II. Evolution of 557 GHz 110-101 emission in low-mass protostars (2012, methodology): “The non-LTE statistical equilibrium radiative transfer code RADEX (van der Tak et al. 2007) is used to estimate the abundance of H2O with respect to CO in the optically thin limit.”
• Global collapse of molecular clouds as a formation mechanism for the most massive stars (2013, methodology): “SDC335 is well enough characterised that we can estimate the HCO+ abundance using the 1D non-LTE RADEX radiative transfer code (van der Tak et al. 2007).”
• OBSERVATIONS OF Arp 220 USING HERSCHEL-SPIRE: AN UNPRECEDENTED VIEW OF THE MOLECULAR GAS IN AN EXTREME STAR FORMATION ENVIRONMENT (2011, methodology): “We used the full observed CO SLED from J = 1-0 to J = 13-12, with the exception of the J = 10-9 line, which is blended with a water line (see Figure 2 (f)), to model the CO excitation and radiative transfer using a variant of the non-LTE code, RADEX (van der Tak et al. 2007).”
• THE RELATION BETWEEN GAS AND DUST IN THE TAURUS MOLECULAR CLOUD (2010, methodology): “We use the RADEX program (van der Tak et al. 2007), using the LVG approximation, and the collision cross sections from the Leiden Atomic and Molecular Database (LAMDA; Schöier et al. 2005), to compute line intensi- ties.”
• Ammonia from cold high-mass clumps discovered in the inner Galactic disk by the ATLASGAL survey (2012, methodology): “To investigate the deviation of the excitation temperature from the kinetic temperature, we used the non LTE molecular radiative transfer program RADEX (van der Tak et al. 2007).”
• A Herschel/PACS Far-infrared Line Emission Survey of Local Luminous Infrared Galaxies (2017, methodology): “We have used the statistical equilibrium radiative transfer code RADEX (van der Tak et al. 2007), to model the variation of the [O i]63/[C ii] PDR 158 ratio as a function of the kinetic temperature of the gas (T kingas ), assuming T kin gas = η Tdust.”
• Dense gas in the Galactic central molecular zone is warm and heated by turbulence (2015, methodology): “We use RADEX (van der Tak et al. 2007) and a related solver (Fujun Du’s myRadex; https://github.com/fjdu/ myRadex) to create model grids for the p-H2CO lines over a grid of 20 densities (n = 102.5-107 cm−3), a fixed assumed5 line gradient of 5 km s−1pc−1, 30 H2CO column densities N(H2CO) = 1 × 1011…”