2006ApJ...645..115R -
Astrophys. J., 645, 115-133 (2006/July-1)
Why X-ray-selected active galactic nuclei appear optically dull.
RIGBY J.R., RIEKE G.H., DONLEY J.L., ALONSO-HERRERO A. and PEREZ-GONZALEZ P.G.
Abstract (from CDS):
We investigate why half of X-ray-selected active galactic nuclei (AGNs) in deep surveys lack signs of accretion in their optical spectra. The majority of these ``optically dull'' AGNs are no more than ∼6 times fainter than their host galaxies in rest-frame R band; as such, AGN lines are unlikely to be overwhelmed by stellar continuum in at least half the sample. We find that optically dull AGNs have the mid-infrared emission and LX/LIRratios characteristic of local Seyfert galaxies, suggesting that the cause of optical dullness is not missing UV-optical continua. We compare the morphologies of 22 optically dull and 9 optically active AGNs at 0.5<z<0.8 and find that optically dull AGNs show a wide range of axis ratio, but optically active AGNs have only very round axis ratios. We conclude that hard X-rays select AGNs in host galaxies with a wide range of inclination angle, but only those AGNs in the most face-on or spheroidal host galaxies show optical emission lines. Thus, extranuclear dust in the host galaxy plays an important role in hiding the emission lines of optically dull AGNs.
Abstract Copyright:
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Journal keyword(s):
Galaxies: Active - Infrared: Galaxies - X-Rays: Galaxies
Simbad objects:
97
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