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Issue A&A
Volume 392, Number 3, September IV 2002
Page(s) 827 - 839
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20020951



A&A 392, 827-839 (2002)
DOI: 10.1051/0004-6361:20020951

Radiative transfer with finite elements

II. Ly $\alpha$ line transfer in moving media
E. Meinköhn1, 2 and S. Richling1

1  Institut für Theoretische Astrophysik, Universität Heidelberg, Tiergartenstr. 15, 69121 Heidelberg
2  Institut für Angewandte Mathematik, Universität Heidelberg, Im Neuenheimer Feld 294, 69120 Heidelberg

(Received 8 May 2002 / Accepted 24 June 2002 )

Abstract
A finite element method for solving the resonance line transfer problem in moving media is presented. The algorithm works in three spatial dimensions on unstructured grids which are adaptively refined by means of an a posteriori error indicator. Frequency discretization is implemented via a first-order Euler scheme. We discuss the resulting matrix structure for coherent isotropic scattering and complete redistribution. The solution is performed using an iterative procedure, where monochromatic radiative transfer problems are successively solved. The present implementation is applicable for arbitrary model configurations with an optical depth up to 103-4. Results of Ly $\alpha$ line transfer calculations for a spherically symmetric model, a disk-like configuration, and a halo containing three source regions are discussed. We find the characteristic double-peaked Ly $\alpha$ line profile for all models with an optical depth $\ga$1. In general, the blue peak of the profile is enhanced for models with infall motion and the red peak for models with outflow motion. Both velocity fields produce a triangular shape in the two-dimensional Ly $\alpha$ spectra, whereas rotation creates a shear pattern. Frequency-resolved Ly $\alpha$ images may help to find the number and position of multiple Ly $\alpha$ sources located in a single halo. A qualitative comparison with observations of extended Ly $\alpha$ halos associated with high redshift galaxies shows that even models with lower hydrogen column densities than required from profile fitting yield results which reproduce many features in the observed line profiles and two-dimensional spectra.


Key words: line: formation -- radiative transfer -- scattering -- methods: numerical -- galaxies: high-redshift

Offprint request: S. Richling, richling@ita.uni-heidelberg.de

SIMBAD Objects in preparation



© ESO 2002


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