Journal Article

Frying doughnuts: what can the reprocessing of X-rays to IR tell us about the AGN environment?

B. McKernan, K. E. S. Ford, N. Chang and C. S. Reynolds

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 394, issue 1, pages 491-500
Published in print March 2009 | ISSN: 0035-8711
Published online March 2009 | e-ISSN: 1365-2966 | DOI:
Frying doughnuts: what can the reprocessing of X-rays to IR tell us about the AGN environment?

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Active galactic nuclei (AGN) produce vast amounts of high-energy radiation deep in their central engines. X-rays either escape the AGN or are absorbed and re-emitted mostly as infrared (IR). By studying the dispersion in the ratio of observed mid-IR luminosity to observed 2–10 keV X-ray luminosity (RIR/X) in AGN, we can investigate the reprocessing material (possibly a torus or donut of dust) in the AGN central engine, independent of model assumptions.

We studied the ratio of observed mid-IR and 2–10 keV X-ray luminosities in a heterogeneous sample of 245 AGN from the literature. We found that when we removed AGN with prominent jets, ∼90 per cent of type I AGN lay within a very tight dispersion in luminosity ratio (1 < RIR/X < 30). This implies that the AGN central engine is extremely uniform and models of the physical AGN environment (e.g. cloud cover, turbulent disc, opening angle of absorbing structures such as dusty tori) must span a very narrow range of parameters. We also found that the far-IR (100 μm) to mid-IR (12 μm) observed luminosity ratio is an effective discriminator between heavily obscured AGN and relatively unobscured AGN.

Keywords: galaxies: active; galaxies: individual; galaxies: Seyfert; techniques: spectroscopic

Journal Article.  8899 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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