He i lines in the spectra of QSOs and Seyfert galaxies

Detailed calculations of He i line strengths for several models of QSOs and Seyfert galaxy nuclei are given. It is shown that an enhancement of the He i lambda5876 and He i lambda7065 lines by a factor of approx.2-10, is caused near quasars in emission regions 1-3 pc in diameter (0.1-0.3 pc for Seyfert galaxies). Line enhancement is practically independent of the gas density as long as N/sub H/> or approx. =2 x 109 cm-3, and is a function of distance from the ionizing continuum source. The broad and strong He i lines observed in the spectrum of some active objects are discussed. It is argued that in the cases where the He i lambda5876 line shows a broader profile than Hβ, and possibly in other cases, the lines are formed in a gravitationally bound system, rather than in an atmosphere expanding under radiation pressure forces