SIMBAD references

To study the evolution of the absorbing clouds in the so-called Lyman forest in the spectra of high redshift QSOs, a sample of 50 well studied objects is collected from the literature together with some new data. The statistical analysis of the redshift distribution of the Lyman-α lines supports a strong increase of the line densities at high redshifts (if dN/dz ∝(1+z)^γ, γ=2.44±0.24). In addition, a flattening in the line distribution is indicated at the lowest redshifts accessible from the ground (z<2.3), consistent with recent HST observations. If at all, there is only a very weak indication of the so-called inverse effect, attributed to the Stroemgren sphere of the QSO under study. A behaviour similar to this effect may be generated by a flattening of the distribution of Lyman-lines at low redshifts.