24 Micron properties of X-ray-selected active galactic nuclei

J. R. Rigby, G. H. Rieke, R. Maiolino, R. Gilli, C. Papovich, P. G. Pérez-Gonzàlez, A. Alonso-Herrero, E. Le Floc'h, C. W. Engelbracht, K. Gordon, D. C. Hines, J. L. Hinz, J. E. Morrison, J. Muzerolle, M. J. Rieke, K. Y.L. Su

Research output: Contribution to journalArticlepeer-review

36 Scopus citations


We examine the 24 μm to X-ray color of 157 X-ray-selected active galactic nuclei (AGNs) as a function of X-ray obscuration and optical classification in the Chandra Deep Field-South. The sample consists of the Chandra hard-band detections with 2-8 keV flux above 10-15 ergs s-1 cm-2. A deep 24 μm mosaic obtained with Spitzer provides mid-infrared fluxes for the sample. Since obscured AGNs locally have higher 24 μm/2-8 keV flux ratios than unobscured AGNs, and since X-ray background models predict a large population of obscured AGNs, we expect to find many X-ray-hard, IR-bright AGNs. Instead, we find that the 24 μm to X-ray flux ratio does not depend on X-ray hardness in the full sample, nor does it differ between narrow- and broad-line AGNs. We identify five nearly Compton-thick AGNs and find they have similar 24 μm to X-ray flux ratios compared to the full sample. We consider AGNs in the narrow redshift spikes at z ∼ 0.7; for these AGNs, there is some evidence that the flux ratio increases with X-ray hardness. The redshift slice also shows an odd trend that is also prominent in the full sample: a group of X-ray-hard AGNs with very low 24 μm to X-ray flux ratios.

Original languageEnglish (US)
Pages (from-to)160-165
Number of pages6
JournalAstrophysical Journal, Supplement Series
Issue number1
StatePublished - Sep 2004


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

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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