High-Ionization Nuclear Emission-Line Region in the Seyfert Galaxy Tololo 0109−383

Abstract

We present a detailed optical spectroscopic analysis of the high-ionization Seyfert galaxy Tololo 0109-383, which was classified originally as a type 2 Seyfert nucleus. The high-ionization nuclear emission-line region (HINER) (traced by e.g., [Fe X] λ6374) of this galaxy is found to be spatially extended. Although the total radial extent of the HINER amounts to ~1.1 kpc, ~70% of the HINER emission is concentrated in the inner 220 pc in radius. The inner HINER in Tololo 0109-383 can be interpreted by the photoionization model of Ferguson, Korista, & Ferland, while the extended HINER suggests that low-density interstellar medium is also photoionized by high-energy continuum emission as described by Korista & Ferland. We find an extended low-ionization emission line region traced by Hα, [N II], and [S II] emission lines with very narrow widths (<200 km s-1) at ~2.2 kpc east of the nucleus. This region is characterized by (1) the observed [N II]/Hα ratio, which is ~0.8; (2) no measurable [O III] emission; and (3) a low ionization parameter, U ~ 6 × 10-5. These properties can also be interpreted in terms of a photoionization model. As well as confirmation of the presence of broad emission in both Hα and Hβ lines, we also find optical Fe II emission features in our spectra. Since the optical Fe II emission is one of the important characteristics of type 1 active galactic nuclei, it is shown that Tololo 0109-383 harbors a type 1 central engine in its nucleus. Since the soft X-ray–to–infrared (60 μm) luminosity ratio of Tololo 0109-383 is higher than those of typical type 2 Seyfert nuclei, we consider that blocking by a dusty torus may be incomplete and thus we are able to observe the type 1 nature of Tololo 0109-383.