The spectral energy distribution of the
central parsec-scaled region of AGN
Prieto, M. A., Reunanen, J., Beckert,
Th., Tristram, K.R.W., Neumayer, N., Fernandez-Ontiveros, J.A., Acosta,
J.
Talk presented at the Conference "The Central
Engine of Active Galactic Nuclei"
held in Xian, China on 16 - 21 October, 2006.
Conference proceedings ed. L. C. Ho and J.-M. Wang (San Francisco: ASP)
ASP Conference Series, Vol. 373, p.600 (2007)
Abstract
Genuine spectral energy distributions (SEDs) of the central few parsec
of the nearest and brightest active galaxies in the Southern Hemisphere
are presented. They are compiled from very high spatial resolution
observations in the radio (VLBA), the infrared (using adaptive optics
and interferometry) and the optical (HST). The SEDs are characterized
by two main emission bumps peaking in the X-rays and in the infrared
respectively, as it is known from optically obscured galactic nuclei.
Yet, the SED shape of the IR largely departs from the one derived from
large aperture data. It reveals two new features: (1) a very sharp
decay at wavelengths shortward of 2 $\mu$m, plausibly a consequence of
the heavy extinction towards the core region and (2) a flattening in
the 10-20 $\mu$m range as well as a downturn toward longer wavelengths.
Accordingly, the true bolometric luminosity of these core regions turns
out to be about an order of magnitude lower than previously estimated
on the basis of IRAS/ISO data. These findings indicate that large
aperture IR data are largely dominated by the contribution of the host
galaxy. They warn against over-interpretations of IR/X-ray and
IR/optical correlations based on large aperture IR data which are used
to differentiate AGN from normal galaxy populations.
The new derived IR bolometric luminosities still exceed the output
energy measured in the high energies by factors from 3 to 60. With the
expectation that both luminosities should be comparable within an order
of magnitude, the reduced factors between both suggests that the
derived IR luminosities are getting closer to the genuine power output
of the core.
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