An Empirical Ultraviolet Template for Iron Emission in Quasars as Derived from I Zwicky 1

We present an empirical template spectrum suitable for fitting/subtractingand studying the FeII and FeIII line emission in the restframe UV spectra ofactive galatic nuclei (AGNs), the first empirical UV iron template to cover thefull 1250 - 3090 A range. Iron emission is often a severe contaminant inoptical--UV spectra of AGNs. Its presence complicates and limits the accuracyof measurements of both strong and weak emission lines and the continuumemission, affecting studies of line and continuum interrelations, theionization structure, and elemental abundances in AGNs. Despite the wealth ofwork on modeling the AGN FeII emission and the need to account for it inobserved AGN spectra, there is no UV template electronically available to aidthis process. The iron template we present is based on HST spectra of theNarrow Line Seyfert 1, IZw1. Its intrinsic narrow lines (~900 km/s) and richiron spectrum make the template particularly suitable for use with most AGNspectra. The iron emission spectrum and the line identifications andmeasurements are presented and compared with the work of Laor et al. Weillustrate the application of the derived FeII and FeIII templates by fittingand subtracting the iron emission from UV spectra of four high-z quasars and ofthe nearby quasar, 3C273. We briefly discuss the small discrepancies betweenthis observed iron emission and the UV template, and compare the template withpreviously published ones. We discuss the advantages and limitations of thetemplates and of the template fitting method. We conclude that the templateswork sufficiently well to be a valuable and important tool for eliminating andstudying the iron emission in AGNs, at least until accurate theoretical ironemission models are developed. (Abridged)