Reliability of NH3 as the temperature probe of cold cloud cores
| Autor: | Mika Juvela, Nathalie Ysard, T. Lunttila, Jorma Harju |
|---|---|
| Přispěvatelé: | Department of Physics [Helsinki], Falculty of Science [Helsinki], University of Helsinki-University of Helsinki, Institut d'astrophysique spatiale (IAS), Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), foreign laboratories (FL), CERN [Genève] |
| Jazyk: | angličtina |
| Rok vydání: | 2012 |
| Předmět: |
Mean kinetic temperature
Interstellar cloud FOS: Physical sciences Astrophysics Kinetic energy 01 natural sciences ISM: clouds Spectral line 0103 physical sciences 010306 general physics Spectroscopy 010303 astronomy & astrophysics Optical depth Astrophysics::Galaxy Astrophysics Line (formation) Physics radio lines: ISM stars: formation Astronomy and Astrophysics Astrophysics - Astrophysics of Galaxies ISM: molecules Computational physics 13. Climate action Space and Planetary Science radiative transfer [SDU]Sciences of the Universe [physics] Astrophysics of Galaxies (astro-ph.GA) Saturation (chemistry) |
| Zdroj: | Astronomy and Astrophysics-A&A Astronomy and Astrophysics-A&A, EDP Sciences, 2012, 538, pp.A133. ⟨10.1051/0004-6361/201118257⟩ |
| ISSN: | 0004-6361 |
| Popis: | The temperature is a central parameter affecting the chemical and physical properties of dense cores of interstellar clouds and their evolution to star formation. The chemistry and the dust properties are temperature dependent and the interpretation of observation requires the knowledge of the temperature and its variations. Measurement of the gas kinetic temperature is possible with molecular line spectroscopy, the ammonia molecule, NH3, being the most commonly used tracer. We want to determine the accuracy of the temperature estimates derived from ammonia spectra. The normal interpretation of NH3 observations assumes that all the hyperfine line components are tracing the same gas volume. In the case of temperature gradients they may be sensitive to different layers and cause errors in the optical depth and gas temperature estimates. We examine a series of spherical cloud models, 1.0 and 0.5 M_Sun Bonnor-Ebert spheres, with different radial temperature profiles. We calculate synthetic NH3 spectra and compare the derived column densities and temperatures to the true values. For high signal-to-noise observations, the estimated gas kinetic temperatures are within ~0.3 K of the real mass averaged temperature and the column densities are correct to within ~10%. When the S/N ratio of the (2,2) spectrum decreases below 10, the temperature errors are of the order of 1K but without a significant bias. When the density of the models is increased by a factor of a few, the results begin to show significant bias because of the saturation of the (1,1) main group. The ammonia spectra are found to be a reliable tracer of the mass averaged gas temperature. Because the radial temperature profiles of the cores are not well constrained, the central temperature could still differ from this value. If the cores are optically very thick, there are no guarantees of the accuracy. 7 pages, accepted to A&A |
| Databáze: | OpenAIRE |
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