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Resolving the mid-infrared cores of local Seyferts | P. Gandhi
; H. Horst
; A. Smette
; S. Hoenig
; A. Comastri
; R. Gilli
; C. Vignali
; W. Duschl
; | Date: |
16 Feb 2009 | Abstract: | We present new photometry of 16 local Seyferts including 6 Compton-thick
sources in N-band filters around 12-microns, 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 micron:2-10 keV) luminosity correlation. Performing a
physically-motivated sub-selection of sources in which the Seyfert torus is
likely to be best-resolved results in the correlation L_{MIR} ~
L_X^{1.11+/-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 micron spectral index (alpha_IX)
is found to be -1.10+/-0.01, largely independent of luminosity. Observed
12-micron bolometric corrections range over ~10-30 if a known luminosity trend
of intrinsic X-ray bolometric corrections is assumed. Comparison with ISO data
spanning a larger luminosity range suggests that our correlation can be
extended into the quasar regime. The fact 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
the tightness of the correlation constrains any residual star-formation within
these physical scales, for which we infer a mean upper-limit of <~40% of the
remaining unresolved flux. We suggest that uncontaminated mid-IR continuum
imaging of AGN is an accurate proxy for their intrinsic power. | Source: | arXiv, 0902.2777 | Services: | Forum | Review | PDF | Favorites |
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