[138.01] The Far-Infrared$-$X-ray Spectral Energy Distributions of X-ray-selected Active Galaxies.

AAS 201st Meeting, January, 2003
Session 138. X-Ray Observations of Quasars and AGNs
Oral, Thursday, January 9, 2003, 2:00-3:30pm, 616-617

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[138.01] The Far-Infrared-X-ray Spectral Energy Distributions of X-ray-selected Active Galaxies.

B. Wilkes, J. Kuraszkiewicz (Harvard-Smithsonian CfA), E. Hooper (UT), K. Wood (St. Andrews), J. Bjorkman (Ritter), K. Delain (UMN), M. Elvis (Harvard-Smithsonian CfA), D. Hughes (INAOE), C. Impey (UofA), C. J. Lonsdale (IPAC), M. Malkan (UCLA), K. McLeod (Wellesley), J. McDowell (Harvard-Smithsonian CfA), B. Whitney (SSI)

Hard X-ray selection is, arguably, the optimal method for defining a representative sample of active galactic nuclei (AGN). Hard X-rays are unbiased by the affects of obscuration and re-processing along the line-of-sight intrinsic/external to the AGN which result in unknown fractions of the population being missed from traditional optical/soft-X-ray samples. We present the far-infrared (IR) observations of 22 hard X-ray selected AGN from the HEAO-1 A2 sample observed with the Infrared Space Observatory (ISO). The sample also shows a wider range of optical/UV shapes than the optically/radio-selected samples, extending to redder near-IR colors. The redder AGN are mostly intermediate or type 2 Seyferts. We find that the mid-IR colors of type 1 and 2 AGNs are similar, indicating column densities, log N_H ~22, lower than those of standard optically thick torus models for AGN. Our results support more complex models in which the amount of obscuring material increases with viewing angle and may be clumpy. Such a scenario, already suggested by differing optical/near-IR spectroscopic and X-ray AGN classifications, allows for different amounts of obscuration of the continuum emission in different wavebands and of the broad emission line region. The lower optical depth of the obscuring material also allows the AGN to heat more dust at larger radial distances. We show that an AGN-heated, flared, dusty disk with mass ~10⁹ {{\rm M_\odot}} and size ~00 - 300 pc can reproduce the wide range of optical-far-IR spectral energy distributions (SEDs) present in our sample with no need for an additional starburst component to generate the long-wavelength, cooler part of the IR continuum. We gratefully acknowledge the financial support of NASA grant number: NAG5-8847 (ISO)

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