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

A new method, based on the simulated annealing al- gorithm and aimed at the inverse problem in the analysis of in- tergalactic (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 Min- imization 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 syn- thetic spectra that emulate the up-to-date best quality data. H i, Cii ,S iii ,C iv ,S iiv, and Ovi lines, exhibiting complex pro- files, were fitted simultaneously. The adopted physical parame- ters have been recovered with a sufficiently high accuracy. The results obtained encourage the application of the proposed pro- cedure to the analysis of real observational data.