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Astron. Astrophys. 356, 1149-1156 (2000)

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Free-free and recombination radiation from massive star-forming regions

T. Beckert 1,2, W.J. Duschl 1,3 and P.G. Mezger 3

1 Institut für Theoretische Astrophysik, Tiergartenstrasse 15, 69121 Heidelberg, Germany
2 Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
3 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received 26 August 1999 / Accepted 25 February 2000

Abstract

The contribution of free-free and recombination radiation to the IR emission from regions of massive star formation is investigated. A method for calculating Gaunt factors for free-free emission from a hydrogenic non-relativistic gas is employed and the results are compared with approximation formula from the literature. While the cooling of ionized star forming regions due to free-free and free-bound transitions emerges in the MIR, which is dominated by dust emission, the overall cooling is mainly provided by line emission of heavier elements. Only in metal-free and therefore dust-free H II regions can free-free and free-bound radiation become dominant. We investigate the global energy balance of those regions and determine temperatures of the ionized gas, which are in general 2 to 8 times larger than found in present day star forming regions of massive stars.

Key words: radiation mechanisms: thermal – ISM: H ii regions – infrared: ISM: continuum – radio continuum: general – radio continuum: ISM

Send offprint requests to: W.J. Duschl, Institut für Theoretische Astrophysik, Tiergartenstrasse 15, 69121 Heidelberg, Germany (wjd@ita.uni-heidelberg.de)

Correspondence to: W.J. Duschl, Institut für Theoretische Astrophysik, Tiergartenstrasse 15, 69121 Heidelberg, Germany (wjd@ita.uni-heidelberg.de)

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© European Southern Observatory (ESO) 2000

Online publication: April 17, 2000
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