Redshift distribution of Lyα lines and metal systems

The observed redshift distribution of Ly alpha lines and metal systems is examined in order to discriminate and to trace the evolution of structure elements observed in the galaxy distribution, at small redshifts, and to test the theoretical description of structure evolution. We show that the expected evolution of a filamentary component of structure describes quite well the redshift distribution of metal systems and stronger Ly alpha lines with log(N-HI)greater than or equal to 14, at z less than or equal to3. The redshift distribution of weaker Ly alpha lines can be attributed to the population of poorer structure elements (Zel'dovich pancakes), which were formed at high redshifts from the invisible dark matter and non-luminous baryonic matter, and which at lower redshifts are mainly merged and dispersed.