Abstract
The effects of a finite correlation length of a turbulent velocity field on the line formation process are considered for hydrogen absorption lines observed in quasar spectra. It is shown that both thermal and large-scale stochastic motions with a finite correlation length (0<l<∞) lead in general tosmaller equivalent widths of hydrogen lines than in the case when macroscopic motions are assumed to be completely uncorrelated (l≡0). Different influence of this effect on optically thin and thick absorption lines allows us to measure eventually turbulent characteristics of the gas in the Lyα forest clouds. It is emphasized that possible measurements of the deuterium abundance in the early Universe could yield systematically higher ratios of D/H if the finite-correlation-length effects are ignored.
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