ACCRETION RATE AND THE PHYSICAL NATURE OF UNOBSCURED ACTIVE GALAXIES
- Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany)
- Physics Department and Yale Center for Astronomy and Astrophysics, Yale University, New Haven, CT 06511 (United States)
- Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)
- Research Center for Space and Cosmic Evolution, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577 (Japan)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Astrophysical Observatory, Department of Engineering Science and Physics, City University of New York, College of Staten Island, 2800 Victory Blvd., Staten Island, NY 10314 (United States)
- European Southern Observatory, Karl-Schwarschild-Strasse 2, D-85748 Garching (Germany)
- California Institute of Technology, MC 105-24, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
We show how accretion rate governs the physical properties of a sample of unobscured broad-line, narrow-line, and lineless active galactic nuclei (AGNs). We avoid the systematic errors plaguing previous studies of AGN accretion rates by using accurate intrinsic accretion luminosities (L{sub int}) from well-sampled multiwavelength spectral energy distributions from the Cosmic Evolution Survey, and accurate black hole masses derived from virial scaling relations (for broad-line AGNs) or host-AGN relations (for narrow-line and lineless AGNs). In general, broad emission lines are present only at the highest accretion rates (L{sub int}/L{sub Edd} > 10{sup -2}), and these rapidly accreting AGNs are observed as broad-line AGNs or possibly as obscured narrow-line AGNs. Narrow-line and lineless AGNs at lower specific accretion rates (L{sub int}/L{sub Edd} < 10{sup -2}) are unobscured and yet lack a broad-line region. The disappearance of the broad emission lines is caused by an expanding radiatively inefficient accretion flow (RIAF) at the inner radius of the accretion disk. The presence of the RIAF also drives L{sub int}/L{sub Edd} < 10{sup -2} narrow-line and lineless AGNs to have ratios of radio-to-optical/UV emission that are 10 times higher than L{sub int}/L{sub Edd} > 10{sup -2} broad-line AGNs, since the unbound nature of the RIAF means it is easier to form a radio outflow. The IR torus signature also tends to become weaker or disappear from L{sub int}/L{sub Edd} < 10{sup -2} AGNs, although there may be additional mid-IR synchrotron emission associated with the RIAF. Together, these results suggest that specific accretion rate is an important physical 'axis' of AGN unification, as described by a simple model.
- OSTI ID:
- 21576762
- Journal Information:
- Astrophysical Journal, Vol. 733, Issue 1; Other Information: DOI: 10.1088/0004-637X/733/1/60; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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