High-redshift QSO absorbing clouds and the background ionizing source

Abstract

Echelle spectra of the high-redshift QSO PKS 2000-330 have been analyzed to provide redshifts, H I column densities, and velocity dispersions of Lyman line absorbing systems in the redshift range of 3.02-3.75. The H I column density distribution function may not be well approximated by a power law, as had been suggested in earlier work, but instead shows a possible flattening towards lower values of the H I column density. For simple uniform cloud models, the redshift evolution of this distribution could in principle be used to infer the redshift dependence of the density of the gas within the clouds. It is found that the source of ionization of these clouds cannot be the integrated light from background quasars, if the quasar density distribution cuts off between z of about 2 and z of about 4 as is commonly thought. 25 references.