On the origin of broad Fe Kα and H I Hα lines in active galactic nuclei

We examine the properties of the Fe emission lines that arise near 6.4 keV in the ASCA spectra of AGNs. Our emphasis is on the Seyfert 1 galaxies where broad and apparently complex Fe K alpha emission is observed. We consider various origins for the line but focus on the pros and cons for line-emitting accretion disk models. We develop a simple model of an illuminated disk capable of producing both X-ray and optical lines. The model is able to reproduce the observed Fe K alpha FWHM ratio as well as the radii of maximum emissivity implied by the profile redshifts. The overall profile shapes, however, do not fit well the predictions of our disk illumination model nor do we derive always consistent disk inclinations for the two lines. We conclude that the evidence for and against an accretion disk origin for the Fe K alpha emission is equivocal. The bulk of the data requires a very disparate set of line fits, shedding little light on a coherent physical model. We briefly consider alternatives to disk-emission and show that a simple bicone model can reproduce the Fe line profiles equally well.