The High-Ionization Nuclear Emission-Line Region of Seyfert Galaxies

Abstract

Recently Murayama & Taniguchi proposed that a significant part of the high-ionization nuclear emission-line region (HINER) in Seyfert nuclei arises from the inner wall of dusty tori because type 1 Seyfert nuclei (S1s) show the excess HINER emission with respect to type 2 Seyfert ones (S2s). This means that the radiation from the HINER has the anisotropic property and thus statistical properties of the HINER emission can be used to investigate the viewing angle toward dusty tori for various types of Seyfert nuclei. In order to investigate viewing angles toward various types of Seyferys, we apply this HINER test to them. Our main results are as follows. (1) The NLS1s are viewed from a more face-on view toward dusty tori than the S2s. However, the HINER properties of the NLS1s are indistinguishable from those of the S1s. (2) The type 1.5 Seyferts appear to comprise heterogeneous populations. (3) The type 1.8 and 1.9 Seyferts and the objects showing either a broad Pa_beta line or polarized broad Balmer lines are seen from a large inclination angle and the emission from the BLRs of such objects reaches us through optically-thin parts of dusty tori. These three results support strongly the current unified model of Seyfert nuclei. And, (4) the line ratios of [Fe X]6374 to the low-ionization emission-lines have rather isotropic property than those of [Fe VII]6087. Therefore it is suggested that the [Fe X] emission is not useful investigating the viewing angle toward the dusty torus in Seyfert nuclei. The most plausible reason seems that the [Fe X] emission is spatially extended and thus its strength tends to show less viewing angle dependence.