D. Asmus, S. F. Hönig, P. Gandhi, A. Smette, W. J. Duschl
We present ground-based high-spatial resolution mid-infrared (MIR)
observations of 20 nearby low-luminosity AGN (LLAGN) with VLT/VISIR and the
preliminary analysis of a new sample of 10 low-luminosity Seyferts observed
with Gemini/Michelle. LLAGN are of great interest because these objects are the
most common among active galaxies, especially in the nearby universe. Studying
them in great detail makes it possible to investigate the AGN evolution over
cosmic timescale. Indeed, many LLAGN likely represent the final stage of an
AGN's lifetime. We show that even at low luminosities and accretion rates
nuclear unresolved MIR emission is present in most objects. Compared to lower
spatial resolution Spitzer/IRS spectra, the high-resolution MIR photometry
exhibits significantly lower fluxes and different PAH emission feature
properties in many cases. By using scaled Spitzer/IRS spectra of typical
starburst galaxies, we show that the star formation contribution to the 12
micron emission is minor in the central parsecs of most LLAGN. Therefore, the
observed MIR emission in the VISIR and Michelle data is most likely emitted by
the AGN itself, which, for higher luminosity AGN, is interpreted as thermal
emission from a dusty torus. Furthermore, the 12 micron emission of the LLAGN
is strongly correlated with the absorption corrected 2-10 keV luminosity and
the MIR--X-ray correlation found previously for AGN is extended to a range from
10^40 to 10^45 erg/s. This correlation is independent of the object type, and
in particular the low-luminosity Seyferts observed with Michelle fall exactly
on the power-law fit valid for brighter AGN. In addition, no dependency of the
MIR--X-ray ratio on the accretion rate is found. These results are consistent
with the unification model being applicable even in the probed low-luminosity
regime.
View original:
http://arxiv.org/abs/1112.1417
No comments:
Post a Comment