Predicted Fe ii Emission‐Line Strengths from Active Galactic Nuclei

We present theoretical Fe II emission line strengths for physical conditions typical of active galactic nuclei with broad-line regions. The Fe II line strengths were computed with a precise treatment of radiative transfer using extensive and accurate atomic data from the Iron Project. Excitation mechanisms for the Fe II emission included continuum fluorescence, collisional excitation, self-fluorescence among the Fe II transitions, and fluorescent excitation by Lyα and Lyβ. A large Fe II atomic model consisting of 827 fine structure levels (including states to E ≈ 15 eV) was used to predict fluxes for approximately 23,000 Fe II transitions, covering most of the UV, optical, and IR wavelengths of astrophysical interest. Spectral synthesis for wavelengths from 1600 Å to 1.2 μm is presented. Applications of present theoretical templates to the analysis of observations are described. In particular, we discuss recent observations of near-IR Fe II lines in the 8500 Å-1 μm region which are predicted by the Lyα fluorescence mechanism. We also compare our UV spectral synthesis with an empirical iron template for the prototypical, narrow-line Seyfert galaxy I Zw 1. The theoretical Fe II template presented in this work should also be applicable to a variety of objects with Fe II spectra formed under similar excitation conditions, such as supernovae and symbiotic stars.