A New Dual-Component Photoionization Model for the NarrowEmission Line Regions in Active Galactic Nuclei

Having found that type 1 Seyfert nuclei have excess [FeVII]6087 emission withrespect to type 2s, Murayama & Taniguchi have proposed that the high-ionizationnuclear emission-line region (HINER) traced by the [FeVII]6087 emission residesin the inner wall of dusty tori. The covering factor of the torus is usuallylarge (e.g., ~ 0.9). Further, electron density in the tori (e.g., ~ 10^7-10^8cm-3) is considered to be higher significantly than that (e.g., ~ 10^3-10^4cm^-3) in the narrow-line region (NLR). Therefore it is expected that the torusemission contributes to the majority of the higher-ionization emission lines.Taking this HINER component into account, we have constructed newdual-component (i.e., a typical NLR with a HINER torus) photoionization models.Comparison of our model with the observations show that that if the torusemission contributes ~ 10 % of the NLR emission, our dual-component model canexplain the observed high [FeVII]6087/[OIII]5007 intensity ratios of theSeyfert 1s without invoking any unusual assumptions (e.g., the overabundance ofiron).Comment: 12 pages (aaspp4.sty), 2 postscript figures. Accepted for publication in Astrophysical Journal Letter