  The nucleus of the nearby galaxy, NGC 1097, is known to host a young, compact
(r < 9 parsec) nuclear star cluster as well as a low-luminosity active galactic
nucleus (AGN). It has been suggested both that the nuclear stellar cluster is
associated with a dusty torus, and that low-luminosity AGN like NGC 1097 do not
have the torus predicted by the unified model of AGN. To investigate these
contradictory possibilities we have acquired Gemini/T-ReCS 11.7 micron and 18.3
micron images of the central few hundred parsecs of this galaxy at < 45 parsec
angular resolution, in which the nucleus and spectacular, kiloparsec-scale
star-forming ring are detected in both bands. The small-scale mid-infrared
(mid-IR) luminosity implies thermal emission from warm dust close to the
central engine of this galaxy. Fitting of torus models shows that the observed
mid-IR emission cannot be accounted for by dust heated by the central engine.
Rather, the principal source heating the dust in this object is the nuclear
star cluster itself, suggesting that the dust that we detect is not the torus
of AGN unified schemes (although it is also possible that the dusty starburst
itself could provide the obscuration invoked by the unified model). Comparison
of Spitzer/IRS and Gemini/GNIRS spectra shows that, although polyaromatic
hydrocarbon emission (PAH) bands are strong in the immediate circumnuclear
region of the galaxy, PAH emission is weak or absent in the central 19 parsecs.
The lack of PAH emission can probably be explained largely by
destruction/ionization of PAH molecules by hard photons from the nuclear star
cluster. If NGC 1097 is typical, PAH emission bands may not be a useful tool
with which to find very compact nuclear starbursts even in low-luminosity AGN.
