Impacts of a power-law non-thermal electron tail on the ionization and recombination rates

Free access article

Issue		A&A Volume 373, Number 3, July III 2001


Page(s)		1110 - 1124
Section		Physical and chemical processes
DOI		http://dx.doi.org/10.1051/0004-6361:20010667

A&A 373, 1110-1124 (2001)
DOI: 10.1051/0004-6361:20010667

Impacts of a power-law non-thermal electron tail on the ionization and recombination rates

D. Porquet, M. Arnaud and A. Decourchelle

CEA/DSM/DAPNIA, Service d'Astrophysique, C.E. Saclay, 91191 Gif-sur-Yvette Cedex, France

(Received 6 March 2001 / Accepted 27 April 2001 )

Abstract
We have investigated the effects of a non-thermal electron population on the ionization and recombination rates. The considered electron distribution is defined as a Maxwellian function below a break energy E_b and as a power-law function of index $\alpha$ above this energy. We have calculated the collisional (direct and excitation autoionization) ionization coefficient rates as well as the (radiative and dielectronic) recombination rates. Practical methods are given to calculate these rates in order to be easily included in a computer code. The ionization rates are very sensitive to the non-thermal electron population and can be increased by several orders of magnitude depending on the temperature and parameters of the power-law function ( E_b and $\alpha$ ). The non-thermal electrons have a much weaker effect on the (radiative and dielectronic) recombination rates. We have determined the mean electric charge of elements C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni for different values of the break energy and power-law index. The ionization balance is affected significantly, whereas the effect is smaller in ionizing plasmas.

Key words: acceleration of particles -- atomic data -- atomic processes -- radiation mechanisms: non -- thermal -- shock waves -- ISM: supernova remnants

Offprint request: D. Porquet, dporquet@cea.fr

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