Lyα Fluorescent Excitation of Fe II in Active Galactic Nuclei

We have calculated Fe II emission-line strengths for active galactic nuclei broad-line regions using precise radiative transfer and Iron Project atomic data. We improve the treatment of all previously considered excitation mechanisms for the Fe II emission, continuum fluorescence, collisional excitation, fluorescence by self-overlap among the iron lines, and fluorescent excitation by Lyα. We demonstrate that Lyα fluorescence is of fundamental importance in determining the strength of the Fe II emission. In addition to enhancing the ultraviolet and optical Fe II flux, Lyα fluorescence also results in significant near-infrared Fe II emission in the 8500-9500 Å wavelength range. New observations are suggested to probe this effect in strong Fe II-emitting quasars.