The effects of X-ray absorption on the spectra of distant objects.

The X-ray absorption spectrum above 0.1 keV that would be introduced into the continuous X-ray spectrum of a quasar by an intervening uniform, hot intergalactic gas with a small admixture of atoms of C, N, O, Ne, Mg, Si, S and Fe has been calculated in detail. This work is relevant to the well-known search for cosmologically distributed missing mass. The results indicate that soft X-ray absorption can be appreciable for all quasar X-ray sources, from the most distant to the very nearby, for a significant range of IGM temperatures, densities, heavy-element abundances, and observed photon energies. A brief comparison with the preliminary results of the Einstein Observatory quasar sample is made. The possibility that gas 'clumped' on noncosmological scales produces observable absorption lines and/or edges in quasar X-ray spectra is also considered.