Astronomy and Astrophysics, volume 502, 457-472 (2009/8-1)
Resolving the mid-infrared cores of local Seyferts.
GANDHI P., HORST H., SMETTE A., HOENIG S., COMASTRI A., GILLI R., VIGNALI C. and DUSCHL W.
Abstract (from CDS):
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 (12.3µm:2-10keV) luminosity correlation. Performing a physically-motivated subselection of sources in which the Seyfert torus is likely to be best-resolved results in the correlation LMIR∝LX1.11±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 (αIX) 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 ∼70pc 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.
galaxies: active - infrared: galaxies - X-rays: galaxies - galaxies: Seyfert - accretion, accretion disks
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