Monte Carlo inversion of hydrogen and metal lines from QSO absorption   spectra
  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. HI, CII, SiII, CIV, SiIV, and OVI 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. 
Sergei A. Levshakov, Irina I. Agafonova (Ioffe Physico-Technical   Institute, St.Petersburg, Russia), and Wilhelm H. Kegel (...