Why X-ray-selected active galactic nuclei appear optically dull

J. R. Rigby, George H. Rieke, J. L. Donley, A. Alonso-Herrero, P. G. Pérez-González

Research output: Contribution to journalArticle

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Abstract

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/L IR ratios 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.

Original languageEnglish (US)
Pages (from-to)115-133
Number of pages19
JournalAstrophysical Journal
Volume645
Issue number1 I
DOIs
StatePublished - Jul 1 2006

Fingerprint

active galactic nuclei
x rays
galaxies
accretion
dust
luster
continuums
Seyfert galaxies
inclination
light emission
optical spectrum
causes

Keywords

  • Galaxies: active
  • Infrared: galaxies
  • X-rays: galaxies

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Rigby, J. R., Rieke, G. H., Donley, J. L., Alonso-Herrero, A., & Pérez-González, P. G. (2006). Why X-ray-selected active galactic nuclei appear optically dull. Astrophysical Journal, 645(1 I), 115-133. https://doi.org/10.1086/504067

Why X-ray-selected active galactic nuclei appear optically dull. / Rigby, J. R.; Rieke, George H.; Donley, J. L.; Alonso-Herrero, A.; Pérez-González, P. G.

In: Astrophysical Journal, Vol. 645, No. 1 I, 01.07.2006, p. 115-133.

Research output: Contribution to journalArticle

Rigby, JR, Rieke, GH, Donley, JL, Alonso-Herrero, A & Pérez-González, PG 2006, 'Why X-ray-selected active galactic nuclei appear optically dull', Astrophysical Journal, vol. 645, no. 1 I, pp. 115-133. https://doi.org/10.1086/504067
Rigby JR, Rieke GH, Donley JL, Alonso-Herrero A, Pérez-González PG. Why X-ray-selected active galactic nuclei appear optically dull. Astrophysical Journal. 2006 Jul 1;645(1 I):115-133. https://doi.org/10.1086/504067
Rigby, J. R. ; Rieke, George H. ; Donley, J. L. ; Alonso-Herrero, A. ; Pérez-González, P. G. / Why X-ray-selected active galactic nuclei appear optically dull. In: Astrophysical Journal. 2006 ; Vol. 645, No. 1 I. pp. 115-133.
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