The Subaru/XMM-Newton Deep Survey (SXDS). VI. Properties of active galactic nuclei selected by optical variability

Tomoki Morokuma, Mamori Doi, Naoki Yasuda, Masayuki Akiyama, Kazuhiro Sekiguchi, Hisanori Furusawa, Yoshihiro Ueda, Tomonori Totani, Takeshi Oda, Tohru Nagao, Nobunari Kashikawa, Takashi Murayama, Masami Quchi, Mike G. Watson

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


We present the properties of active galactic nuclei (AGN) selected by optical variability in the Subaru/XMM-Newton Deep Field (SXDF). Based on the locations of variable components and light curves, 211 optically variable AGNs were reliably selected. We made three AGN samples; X-ray-detected optically nonvariable AGNs (XAs), X-raydetected optically variable AGNs (XVAs), and X-ray-undetected optically variable AGNs (VAs). In the VA sample, we found a bimodal distribution of the ratio between the variable component flux and the host flux. One of these two components in the distribution, a class of AGNs with a faint variable component i′vari ∼ 25 mag in bright host galaxies i′ ∼ 21 mag, is not seen in the XVA sample. These AGNs are expected to have low Eddington ratios if we naively consider a correlation between bulge luminosity and black hole mass. These galaxies have photometric redshifts Zphoto ∼ 0.5 and we infer that they are low-luminosity AGNs with radiatively inefficient accretion flows (RIAFs). The properties of the XVA and VA objects and the differences from those of the XA objects can be explained within the unified scheme for AGNs. Optical variability selection for AGNs is an independent method and could provide a complementary AGN sample which even deep X-ray surveys have not found.

Original languageEnglish
Pages (from-to)121-130
Number of pages10
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 2008 Mar 20
Externally publishedYes


  • Galaxies: active

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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