The Intergalactic Medium and the Energy Distribution of Quasars

Abstract

The ionizing spectral energy distribution of quasars is known to exhibit a steepening of the distribution short-ward of 1050Å. It has been assumed that this change of power-law index from -1 to -2 is intrinsic to the quasars. We study an alternative interpretation, in which a tenuous absorption screen is responsible for the change of index. A successful spectral fit is obtained using a total hydrogen density distribution decreasing with redshift as $\sim (1+z)^ξ$ with $ξ$ of the order -3.5 if we suppose that the ionization state of the intervening gas is controlled by the line-of-sight quasar. This interpretation is not compatible, however, with the relative weakness of the observed quasar intensities with respect to that of the local background metagalactic radiation. Therefore, our interpretation in its present form cannot be sustained.