Astron. Astrophys. 357, 823-838 (2000)

A code for optically thick and hot photoionized media

A.-M. Dumont, A. Abrassart and S. Collin

Observatoire de Paris, Section de Meudon, Place Janssen, 92195 Meudon, France

Received 1 July 1999 / Accepted 4 February 2000

Abstract

We describe a code designed for hot media (T  a few 10⁴ K), optically thick to Compton scattering. It computes the structure of a plane-parallel slab of gas in thermal and ionization equilibrium, illuminated on one or on both sides by a given spectrum. Contrary to the other photoionization codes, it solves the transfer of the continuum and of the lines in a two stream approximation, without using the local escape probability formalism to approximate the line transfer. We stress the importance of taking into account the returning flux even for small column densities (10²² cm^-2), and we show that the escape probability approximation can lead to strong errors in the thermal and ionization structure, as well as in the emitted spectrum, for a Thomson thickness larger than a few tenths. The transfer code is coupled with a Monte Carlo code which allows to take into account Compton and inverse Compton diffusions, and to compute the spectrum emitted up to MeV energies, in any geometry. Comparisons with cloudy show that it gives similar results for small column densities. Several applications are mentioned.

Key words: radiative transfer galaxies: active ultraviolet: galaxies X-rays: galaxies

Send offprint requests to: Anne-Marie Dumont (Observatoire de Meudon)

© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000

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