Relations between the Optical Fe II Emission and Ultraviolet Spectra in Active Galactic Nuclei

Abstract

Optical Fe II emission is a general characteristic of most active galactic nuclei, but the physical conditions in the Fe II-emitting region are not yet understood. The current photoionization models underpredict the total Fe II intensity as well as optical Fe II/Hβ ratio. In this paper, we report the results of a statistical analysis of the relation between the optical Fe II strength from the literature and the UV spectra from IUE. We find that Fe II/Hβ is strongly correlated with I(λ1400 I(C IV) and I(C iv)/I(Lyα). The equivalent widths of optical Fe II and C IV are significantly anticorrelated. While no firm conclusions have been reached, the Fe II strength might be expected to be influenced by (1) the inclination of the accretion disk, (2) the spectrum of the ionizing continuum, and (3) the volume and column densities of the emission-line gas.