He II Lyman-alpha radiation transfer and Bowen fluorescence in Seyfert galaxies and quasars

The He II Ly-alpha transfer problem and the related O III and N III Bowen fluorescence mechanisms have been investigated for detailed photoionization models of emission-line clouds in Seyfert galaxies and quasars. Transfer results and/or predicted relative intensities of He II or O III far-ultraviolet lines are presented for calculations employing various atomic densities, ionizing radiation characteristics, ionization parameters, chemical abundances, and gas velocity structures. Diagrammed information concerning the fate of diffuse He II Ly-alpha photons should facilitate reasonably accurate model calculations without careful attention to the line transfer. It is also demonstrated that the mean escape probability formalism of Kallman and McCray (1980) compares well with the detailed transfer solution, especially for high-density clouds. The computed average population of the He(+) n = 2 level in these models is consistent with previous estimates used in arguments favoring a recombination origin for the He II lines.