Bibcode
Prieto, M. A.; Reunanen, J.; Beckert, Th.; Tristram, K.; Neumayer, N.; Fernandez, J. A.; Acosta, J.
Bibliographical reference
The Central Engine of Active Galactic Nuclei, ASP Conference Series, Vol. 373, proceedings of the conference held 16-21 October, 2006 at Xi'an Jioatong University, Xi'an, China. Edited by Luis C. Ho and Jian-Min Wang, p.600
Advertised on:
10
2007
Citations
3
Refereed citations
2
Description
Genuine spectral energy distributions (SED) of the central few parsec
region of the nearest and brightest active galaxies in the southern
hemisphere are presented. These are compiled from very high-spatial
resolution data taken from radio (VLBA), IR adaptive optics and
interferometry, and optical (HST) observations. The new SEDs are
characterized by two main emission bumps, each peaking in the X-ray and
IR, respectively, as it is known from optically obscured galactic
nuclei. Yet, the shape of the IR SED largely departs from that derived
from large-aperture data. They reveal two new features: (1) a very sharp
decay at wavelengths shortward of 2 μm, plausibly a consequence of
the heavy extinction towards the core region; and (2) a flattening in
the 10-20 μm range and a further turnover toward longer wavelengths.
Moreover, the true bolometric luminosity of these few parsec 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 may be largely dominated by the
host galaxy contribution, and warn over interpretations of IR/X-ray and
IR/optical correlations based on large-aperture IR data that have been
used to differentiate AGN from normal galaxy populations.
The newly derived IR bolometric luminosities still exceed the output
energy measured in the high energies by factors 3 to 60. On 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. Due to the apparent SED emission turnover in the mid-IR region, an
extrapolation of the VLBA core emission towards shorter wavelengths
closely meets the IR data. In Cen A, NGC 1068 and NGC 5506, this
extrapolation fits a power law with exponent around 1/3. This indicates
that the IR emission may not be so much dust-dominated as previously
thought but includes an important nonthermal component.