THE NATURE OF OPTICALLY DULL ACTIVE GALACTIC NUCLEI IN COSMOS
- Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)
- Research Center for Space and Cosmic Evolution, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577 (Japan)
- Max Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Max Planck Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- California Institute of Technology, MC 105-24, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
- Institute for Astronomy, 2680 Woodlawn Dr., University of Hawaii, Honolulu, HI 96822 (United States)
- Dipartimento di fisica, Universita di Roma La Sapienza, P.le A. Moro 2, 00185 Roma (Italy)
- Observatories of the Carnegie Institute of Washington, Santa Barbara Street, Pasadena, CA 91101 (United States)
- European Southern Observatory, Karl-Schwarschild-Strasse 2, D-85748 Garching (Germany)
We present infrared, optical, and X-ray data of 48 X-ray bright, optically dull active galactic nuclei (AGNs) in the COSMOS field. These objects exhibit the X-ray luminosity of an AGN but lack broad and narrow emission lines in their optical spectrum. We show that despite the lack of optical emission lines, most of these optically dull AGNs are not well described by a typical passive red galaxy spectrum: instead they exhibit weak but significant blue emission like an unobscured AGN. Photometric observations over several years additionally show significant variability in the blue emission of four optically dull AGNs. The nature of the blue and infrared emission suggest that the optically inactive appearance of these AGNs cannot be caused by obscuration intrinsic to the AGNs. Instead, up to approx70% of optically dull AGNs are diluted by their hosts, with bright or simply edge-on hosts lying preferentially within the spectroscopic aperture. The remaining approx30% of optically dull AGNs have anomalously high f{sub X} /f{sub O} ratios and are intrinsically weak, not obscured, in the optical. These optically dull AGNs are best described as a weakly accreting AGN with a truncated accretion disk from a radiatively inefficient accretion flow.
- OSTI ID:
- 21378142
- Journal Information:
- Astrophysical Journal, Vol. 706, Issue 1; Other Information: DOI: 10.1088/0004-637X/706/1/797; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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