INTERGALACTIC ABSORPTION DUE TO EXTENDED GASEOUS CLOUDS AT HIGH REDSHIFTS

In order to examine the line-blanketing effect due to gaseous clouds a t high redshifts, we have calculated the ionization states of gas clou ds of subgalactic mass scale exposed to a UV radiation field that can reproduce the ionization states of the Lyman limit systems (LLSs) alon g the line of sight to quasar HS 1700 + 6416. We also adopted the inte grated UV radiation from the observed quasars modified by the interven ing absorption due to the Lyman a forest and LLSs as an ionizing spect rum. Our photoionization models can explain the observed H I column-de nsity distribution, the observed C IV/H I ratio and the observed optic al depths of H I and He II. We conclude that the integrated UV backgro und models can well explain the ionization states of both the IGM and Lyman alpha clouds at z similar to 2-3. The gaseous mass of the Lyman alpha clouds follows a power-law form as dn/dM(c) proportional to Mc(- delta) with delta similar to 2-2.5 in the 10(8)-10(11) M(.) range. The majority of the dary baryon probably consists of the IGM.