Scattered X-rays in obscured active galactic nuclei and their implications for geometrical structure and evolution

Kazuhisa Noguchi, Yuichi Terashima, Yukiko Ishino, Yasuhiro Hashimoto, Michael Koss, Yoshihiro Ueda, Hisamitsu Awaki

Research output: Contribution to journalArticlepeer-review

32 Citations (Scopus)


We construct a new sample of 32 obscured active galactic nuclei (AGNs) selected from the Second XMM-Newton Serendipitous Source Catalogue to investigate their multiwavelength properties in relation to the "scattering fraction," the ratio of the soft X-ray flux to the absorption-corrected direct emission. The sample covers a broad range of the scattering fraction (∼0.1%-10%). A quarter of the 32 AGNs have a very low scattering fraction (≤ 0.5%), which suggests that they are buried in a geometrically thick torus with a very small opening angle. We investigate correlations between the scattering fraction and multiwavelength properties. We find that AGNs with a small scattering fraction tend to have low [O III]λ5007/X-ray luminosity ratios. This result agrees with the expectation that the extent of the narrow-line region is small because of the small opening angle of the torus. There is no significant correlation between scattering fraction and far-infrared luminosity. This implies that a scale height of the torus is not primarily determined by starburst activity. We also compare scattering fraction with black hole mass or Eddington ratio and find a weak anti-correlation between the Eddington ratio and scattering fraction. This implies that more rapidly growing supermassive black holes tend to have thicker tori.

Original languageEnglish
Pages (from-to)144-156
Number of pages13
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 2010


  • Galaxies: Seyfert
  • Galaxies: active
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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