NOAO >   Observing Info >   Approved Programs >   2007B-0074

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Proposal Information for 2007B-0074


PI: Tomoki Morokuma, National Astronomical Observatory of Japan, tmorokuma@ioa.s.u-tokyo.ac.jp
Address: Division of Optical and Infrared Astronomy, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan

CoI: Mamoru Doi, University of Tokyo
CoI: Naoki Yasuda, University of Tokyo
CoI: Masayuki Akiyama, National Astronomical Observatory of Japan
CoI: Kazuhiro Sekiguchi, National Astronomical Observatory of Japan
CoI: Tomonori Totani, Kyoto University
CoI: Yoshihiro Ueda, Kyoto University

Title: Unveiling the Nature of Optical-Variability-Selected AGN

Abstract: We propose 2-night WIYN/HYDRA spectroscopic observations in order to unveil the nature of active galactic nuclei (AGN) selected by optical variability. Using our large sample of faint variable objects, we have already succeeded in constructing a sample of X-ray undetected optically variable AGN. About half of these AGN have faint variable components (i_\rmvari~25 mag) in apparently normal bright (i~21 mag) galaxies and are expected to have low Eddington ratios. The photometric redshifts, z_\rmphoto~0.5, indicate that luminosity of these AGN is comparable to that of nearby Seyfert nuclei. Their flare-up-like variations can be interpreted as phenomena by radiatively inefficient accretion flow (RIAF). By taking optical spectra of these AGN with WIYN/HYDRA, we mainly investigate their redshift distributions. Considering correlations between bulge mass and supermassive black hole mass, these AGN may be almost at ending phases of mass accretion onto their black holes. Our results indicate that optical variability is a strong tracer for AGN, which is partly independent from and complementary with deep X-ray surveys.


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