Photoionization and the Emission-Line Spectra of Quasi-Stellar Objects

Abstract

Detailed photoionization calculations are used to examine the information conveyed by relative emission-line intensities in QSO spectra. It is found that the elemental abundances cannot be estimated with any assurance; but if “conventional” values are assumed, then certain restrictions may be placed on the ionizing spectra and gas densities. In particular, the ratio between radiation density and gas density is determined. Narrow filaments or sheets of ionized gas seem to be indicated; these may be compressed regions behind shock fronts.