EDP Sciences
Free Access
Volume 418, Number 2, May I 2004
Page(s) 465 - 473
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361:20035838
Published online 09 April 2004

A&A 418, 465-473 (2004)
DOI: 10.1051/0004-6361:20035838

The relation between AGN hard X-ray emission and mid-infrared continuum from ISO spectra: Scatter and unification aspects

D. Lutz1, R. Maiolino2, H. W. W. Spoon3 and A. F. M. Moorwood4

1  Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
2  Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
    e-mail: maiolino@arcetri.astro.it
3  Cornell University, Dept. of Astronomy, 219 Space Science Building, Ithaca, NY 14853-6801, USA
    e-mail: spoon@isc.astro.cornell.edu
4  European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
    e-mail: amoor@eso.org

(Received 10 December 2003 / Accepted 26 January 2004 )

We use mid-infrared spectral decomposition to separate the 6  $\mu$m mid-infrared AGN continuum from the host emission in the ISO low resolution spectra of 71 active galaxies and compare the results to observed and intrinsic 2-10 keV hard X-ray fluxes from the literature. We find a correlation between mid-infrared luminosity and absorption corrected hard X-ray luminosity, but the scatter is about an order of magnitude, significantly larger than previously found with smaller statistics. Main contributors to this scatter are likely variations in the geometry of absorbing dust, and AGN variability in combination with non-simultaneous observations. There is no significant difference between type 1 and type 2 objects in the average ratio of mid-infrared and hard X-ray emission, a result which is not consistent with the most simple version of a unified scheme in which an optically and geometrically thick torus dominates the mid-infrared AGN continuum. Most probably, significant non-torus contributions to the AGN mid-IR continuum are masking the expected difference between the two types of AGN.

Key words: galaxies: active -- galaxies: Seyfert -- infrared: galaxies -- X-rays: galaxies

Offprint request: D. Lutz, lutz@mpe.mpg.de

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