Iron is not Depleted in High-Ionization Nuclear Emission-Line Regions of Active Galactic Nuclei

摘要

In order to examine whether or not high-ionization nuclear emission-lineregions (HINERs) in narrow-line regions of active galactic nuclei are dusty, wefocus on two high-ionization forbidden emission lines, [Fe VII]6087 and [NeV]3426. We perform photoionization model calculations to investigate possibledependences of the flux ratio of [Fe VII]6087/[Ne V]3426 on various gasproperties, in order to investigate how useful this flux ratio to explore thedust abundances in HINERs. Based on our photoionization model calculations, weshow that the observed range of the flux ratio of [Fe VII]6087/[Ne V]3426 isconsistent with the dust-free models while that is hard to be explained by thedusty models. This suggests that iron is not depleted at HINERs, which impliesthat the HINERs are not dusty. This results is consistent with the idea thatthe HINERs are located closer than the dust-sublimation radius (i.e., innerradius of dusty tori) and thus can be hidden by dusty tori when seen from aedge-on view toward the tori, which has been also suggested by the AGN-typedependence of the visibility of high-ionization emission lines.