Theoretical Fei–iiiEmission‐Line Strengths from Active Galactic Nuclei with Broad‐Line Regions

Abstract

We present theoretical iron emission line strengths for physical conditions typical of active galactic nuclei (AGNs) with broad-line regions. The non–local thermodynamic equilibrium (NLTE) models include a new and extensive treatment of radiative transfer in the Fe iii ion, complementing the Fe ii emission line strengths predicted in our earlier works. We also briefly present preliminary results for the Fe i emission from AGNs using a reduced atom model. We can satisfactorily reproduce the empirical UV Fe iii emission line template of Vestergaard & Wilkes for the prototypical narrow-line Seyfert 1 galaxy I Zw 1, both in terms of the general Fe iii flux distribution and the relative strength of the Fe iii and Fe ii emission. However, a number of detailed features are still not matched; the most prominent example is the strongest single Fe iii feature observed in the I Zw 1 spectrum, UV47: it is predicted to be strong only in models suppressing Fe-H charge exchange reactions. We examine the role of variations in cloud turbulent velocity and iron abundance and carry out Monte Carlo simulations to demonstrate the effect of uncertainties in atomic data on the computed spectra. Subject headingg s: atomic data — line: formation — line: identification — quasars: emission lines — supernovae: general