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Title:
Resolving the mid-infrared cores of local Seyferts
Authors:
Gandhi, P.; Horst, H.; Smette, A.; Hönig, S.; Comastri, A.; Gilli, R.; Vignali, C.; Duschl, W.
Affiliation:
AA(RIKEN Cosmic Radiation Lab, 2-1 Hirosawa, Wakoshi, Saitama 351-0198, Japan ), AB(Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel, Leibnizstr. 15, 24098 Kiel, Germany ; Zentrum für Astronomie, ITA, Universität Heidelberg, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany ; Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany), AC(European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago, Chile), AD(Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany), AE(Istituto Nazionale di Astrofisica (INAF) - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy), AF(Istituto Nazionale di Astrofisica (INAF) - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy), AG(Dipartimento di Astronomia, Università degli Studi di Bologna, via Ranzani 1, 40127 Bologna, Italy), AH(Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel, Leibnizstr. 15, 24098 Kiel, Germany)
Publication:
Astronomy and Astrophysics, Volume 502, Issue 2, 2009, pp.457-472 (A&A Homepage)
Publication Date:
08/2009
Origin:
EDP Sciences
Keywords:
galaxies: active, infrared: galaxies, X-rays: galaxies, galaxies: Seyfert, accretion, accretion disks
DOI:
10.1051/0004-6361/200811368
Bibliographic Code:
2009A&A...502..457G

Abstract

We present new photometry of 16 local Seyferts including 6 Compton-thick sources in N-band filters around 12-μm, obtained with the VISIR instrument on the 8-m Very Large Telescope. The near-diffraction-limited imaging provides the least-contaminated core fluxes for these sources to date. Augmenting these with our previous observations and with published intrinsic X-ray fluxes, we form a total sample of 42 sources for which we find a strong mid-infrared:X-ray (12.3 μm:2-10 keV) luminosity correlation. Performing a physically-motivated subselection of sources in which the Seyfert torus is likely to be best-resolved results in the correlation L_MIR ∝ L_X1.11± 0.07, with a reduction of the scatter in luminosities as compared to the full sample. Consideration of systematics suggests a range of 1.02-1.21 for the correlation slope. The mean 2-keV:12.3-μm spectral index (α_IX) is found to be -1.10 ± 0.01, largely independent of luminosity. Indirectly-computed 12-μm bolometric corrections range over ≈10-30 if a known luminosity trend of X-ray bolometric corrections is assumed. Comparison with ISO data spanning a wider luminosity range suggests that our correlation can be extended into the quasar regime. That unobscured, obscured, and Compton-thick sources all closely follow the same luminosity correlation has important implications for the structures of Seyfert cores. The typical resolution-limit of our imaging corresponds to ~70 pc at a median z=0.01, and we use the tightness of the correlation to place constraints on the dominance of any residual emission sources within these physical scales. An upper-limit for any contaminating star formation of ≈40% of the unresolved flux is inferred, on average. We suggest that uncontaminated mid-IR continuum imaging of AGN is an accurate proxy for their intrinsic power.

Based on observations carried out in ESO programme 080.B-0860.

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