Seyfert-type dependences of narrow emission-line ratios and physical properties of high-ionization nuclear emission-line regions in Seyfert galaxies

Tohru Nagao, Takashi Murayama, Yoshiaki Taniguchi

研究成果: Article査読

19 被引用数 (Scopus)

抄録

In order to examine how narrow emission-line flux ratios depend on the Seyfert type, we compiled various narrow emission-line flux ratios of 355 Seyfert galaxies from the literature. We present in this paper that the intensity of the high-ionization emission lines, [Fe VII]λ6087, [Fe x]λ6374, and [Ne v]λ3426, tend to be stronger in Seyfert 1 galaxies than in Seyfert 2 galaxies. In addition to these lines, [O III]λ4363 and [Ne III]λ3869, whose ionization potentials are not high (< 100eV), but whose critical densities are significantly high (≳ 107 cm-3), also exhibit the same tendency. On the other hand, the emission-line flux ratios among low-ionization emission lines do not show such a tendency. We point out that the most plausible interpretation of these results is that the high-ionization emission lines arise mainly from highly-ionized, dense gas clouds, which are located very close to nuclei, and thus can be hidden by dusty tori. To examine the physical properties of these highly-ionized dense gas clouds, photoionization model calculations were performed. As a result, we find that the hydrogen density and the ionization parameter of these highly-ionized dense gas clouds are constrained to be nH > 106 cm-3 and U > 10-22, respectively. These lower limits are almost independent both from the metallicity of gas clouds and from the spectral energy distribution of the nuclear ionizing radiation.

本文言語English
ページ(範囲)629-645
ページ数17
ジャーナルPublications of the Astronomical Society of Japan
53
4
DOI
出版ステータスPublished - 2001

ASJC Scopus subject areas

  • 天文学と天体物理学
  • 宇宙惑星科学

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