New aspects of absorption-line formation in intervening turbulent clouds — III. The inverse problem in the study of H+D profiles

A new method, based on a reverse Monte Carlo technique and aimed at the inverse problem in the analysis of intergalactic (interstellar) H+D absorption profiles, is presented. We consider the process of line formation in media with a stochastic velocity field accounting for correlation effects (mesoturbulence). This approach generalizes the standard microturbulent approximation, which is commonly used to model the formation of absorption spectra in turbulent media. The method allows one to estimate, from an observed spectrum, both the physical parameters of the absorbing gas and an appropriate structure of the distribution of the velocity component parallel to 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. The H+D Lyα, Lyβ and H i Ly-14 lines were fitted simultaneously. The confidence regions calculated for the ‘NH i-D/H’ plane show that the difference between the recovered and adopted values does not exceed the 3σ level.