Redshift distribution of Ly alpha lines and metal systems

The observed redshift distribution of Ly alpha lines and metal systems is e xamined in order to discriminate and to trace the evolution of structure el ements observed in the galaxy distribution, at small redshifts, and to test the theoretical description of structure evolution. We show that the expec ted 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 red shift distribution of weaker Ly alpha lines can be attributed to the popula tion 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.