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Astron. Astrophys. 360, 833-845 (2000)

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Monte Carlo inversion of hydrogen and metal lines from QSO absorption spectra *

S.A. Levshakov 1, I.I. Agafonova 1 and W.H. Kegel 2

1 Department of Theoretical Astrophysics, A.F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, Russia
2 Institut für Theoretische Physik der Universität Frankfurt am Main, 60054 Frankfurt/Main 11, Germany

Received 6 March 2000 / Accepted 23 June 2000


A new method, based on the simulated annealing algorithm and aimed at the inverse problem in the analysis of intergalactic (interstellar) complex spectra of hydrogen and metal lines, is presented. We consider the process of line formation in clumpy stochastic media accounting for fluctuating velocity and density fields (mesoturbulence). This approach generalizes our previous Reverse Monte Carlo and Entropy-Regularized Minimization methods which were applied to velocity fluctuations only. The method allows one to estimate, from an observed system of spectral lines, both the physical parameters of the absorbing gas and appropriate structures of the velocity and density distributions along the line of sight. The validity of the computational procedure is demonstrated using a series of synthetic spectra that emulate the up-to-date best quality data. H I , C II , Si II , C IV , Si IV , and O VI lines, exhibiting complex profiles, were fitted simultaneously. The adopted physical parameters have been recovered with a sufficiently high accuracy. The results obtained encourage the application of the proposed procedure to the analysis of real observational data.

Key words: line: formation – line: profiles – galaxies: quasars: absorption lines – galaxies: quasars: individual: APM 08279+5255

* Based in part on data obtained at the W. M. Keck Observatory, which is jointly operated by the California Institute of Technology, the University of California and the National Aeronautics and Space Administration.

Send offprint requests to: S.A. Levshakov (lev@astro.ioffe.rssi.ru)

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© European Southern Observatory (ESO) 2000

Online publication: August 23, 2000