VLT diffraction-limited imaging at 11 and 18 micron of the nearest
  active galactic nuclei
  Mid-infrared imaging at resolutions of 300 mas of the central kpc region of
13 nearby, well-known active galaxies is presented. The bulk of the mid-IR
emission is concentrated on an unresolved central source within a size of less
than 5 to 130 pc, depending on the object distance. Further resolved emission
is detected in 70% of the sample in the form of circumnuclear star-forming
rings or diffuse nuclear extended emission. In the three cases with
circumnuclear star formation, the stellar contribution is at least as important
as that of the AGN. In those with extended nuclear emission -- a third of the
sample -- this emission represents a few per cent of the total measured;
however, this contribution may be underestimated because of the chopped nature
of these observations. This extended emission is generally collimated in a
preferential direction often coinciding with that of the extended ionized gas
or the jet.
  In all cases, the nuclear fluxes measured at 11.8 and 18.7 micron represent a
minor contribution of the flux levels measured by large aperture IRAS data at
the nearest energy bands of 12 and 25 micron. This contribution ranges from 30%
to less than 10%. In only three cases do the AGN fluxes agree with IRAS to
within a factor of 2. In the AGNs with strong circumnuclear star formation,
this component can well account for most of the IRAS flux measured in these
objects. But in all other cases, either a low surface brightness component
extending over galactic scales or strong extra-nuclear IR sources -- e.g. HII
regions in spiral arms -- have to be the main source of the IRAS emission. In
either case, the contribution of these components dwarfs that of the AGN at
mid-IR wavelengths.
