R E Mason, E Lopez-Rodriguez, C Packham, A Alonso-Herrero, N A Levenson, J Radomski, C Ramos Almeida, L Colina, M Elitzur, I Aretxaga, P F Roche, N Oi
We have obtained high-resolution mid-infrared (MIR) imaging, nuclear spectral
energy distributions (SEDs) and archival Spitzer spectra for 22 low-luminosity
active galactic nuclei (LLAGN; L_bol < 5 x 10^42 erg/s). Infrared (IR)
observations may advance our understanding of the accretion flows in LLAGN, the
fate of the obscuring torus at low accretion rates, and, perhaps, the star
formation histories of these objects. However, while comprehensively studied in
higher-luminosity Seyferts and quasars, the nuclear IR properties of LLAGN have
not yet been well-determined. In these proceedings we summarise the results for
the LLAGN at the relatively high-luminosity, high-Eddington ratio end of the
sample. Strong, compact nuclear sources are visible in the MIR images of these
objects, with luminosities consistent with or slightly in execss of that
predicted by the standard MIR/X-ray relation. Their broadband nuclear SEDs are
diverse; some resemble typical Seyfert nuclei, while others possess less of a
well-defined MIR ``dust bump''. Strong silicate emission is present in many of
these objects. We speculate that this, together with high ratios of silicate
strength to hydrogen column density, could suggest optically thin dust and low
dust-to-gas ratios, in accordance with model predictions that LLAGN do not host
a Seyfert-like obscuring torus.
View original:
http://arxiv.org/abs/1201.4209
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