Infrared Properties of High Redshift and X-ray Selected AGN Samples
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Infrared Properties of High Redshift and X-ray Selected AGN Samples

  • Author(s): Wilkes, BJ
  • Hooper, EJ
  • McLeod, KK
  • Elvis, MS
  • Hughes, DH
  • Impey, CD
  • Kuraszkiewicz, JK
  • Lonsdale, CS
  • Malkan, MA
  • McDowell, JC
  • et al.

The NASA/ISO Key Project on active galactic nuclei (AGN) seeks to better understand the broad-band spectral energy distributions (SEDs) of these sources from radio to X-rays, with particular emphasis on infrared properties. The ISO sample includes a wide variety of AGN types and spans a large redshift range. Two subsamples are considered herein: 8 high-redshift (1 < z < 4.7) quasars; and 22 hard X-ray selected sources. The X-ray selected AGN show a wide range of IR continuum shapes, extending to cooler colors than the optical/radio sample of Elvis et al. (1994). Where a far-IR turnover is clearly observed, the slopes are < 2.5 in all but one case so that non-thermal emission remains a possibility. The highest redshift quasars show extremely strong, hot IR continua requiring ~ 100 solar masses of 500 - 1000 Kelvin dust with ~ 100 times weaker optical emission. Possible explanations for these unusual properties include: reflection of the optical light from material above/below a torus; strong obscuration of the optical continuum; or an intrinsic deficit of optical emission.

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