Bowen fluoresence and He II lines in active galaxies and gaseous nebulae

It is pointed out that emission lines of ionized helium are among the most important diagnostic indicators in the spectrum of active galactic nuclei (AGNs) and other types of gaseous nebulae. Certain difficulties in some investigations are related to the line-continuum overlap problem. In this paper, a new formalism is introduced for handling this problem. The employed technique represents a pure 'escape probability method', involving only the solution of the (nonlinear) level population algebraic equations. The relevant expressions have been incorporated into existing photoionization codes which were utilized to investigate the general problem of ionization and excitation of He II, O III, and N III in gaseous nebulae, giving particular attention to AGN conditions. The new results are presented for ionization and line intensities under a large range of physical conditions, and the arising implications for models of AGNs and other gaseous nebulae are discussed.