Metal systems of the Lyman forest

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An extremely careful analysis of the forest of weak metal-line systems at z 2 has allowed the separation into individual `single-phase ionization' components with accurate parameters. The systems typically span several hundred km/s and within each the components show a strong coherence in their ionization properties. A general feature of the observed systems is the presence of high ionization broad components which co-exist in velocity space with more numerous, narrow, lower ionization components. From a sample of components extending to z 3.5, taken either individually or as system totals, no rapid evolution is found in the column density ratio N(Si IV)/N(C IV), contrary to previous indication of a large change near z = 3.1. Comparisons of component ion ratios including Si IV, C IV, C II and Si II from the sample at z 2 with CLOUDY derived values using several model ionizing spectra show the general dominance of the metagalactic ionizing background over local stellar radiation and give Si/C distributed 1-3 times the solar value. Indications of the evolution of structure are highlighted.