  Why are the nuclei of some galaxies more active than others? If most galaxies
harbor a central massive black hole, the main difference is probably in how
well it is fueled by its surroundings. We investigate the hypothesis that such
a difference can be seen in the detailed circumnuclear morphologies of galaxies
using several quantitatively defined features, including bars, isophotal
twists, boxy and disky isophotes, and strong non-axisymmetric features in
unsharp masked images. These diagnostics are applied to 250 high-resolution
images of galaxy centers obtained in the near-infrared with NICMOS on HST. To
guard against the influence of possible biases and selection effects, we have
carefully matched samples of Seyfert 1, Seyfert 2, LINER, starburst and normal
galaxies in their basic properties, taking particular care to ensure that each
was observed with a similar average scale (10-15 parsecs per pixel). Several
morphological differences among our five different spectroscopic
classifications emerge from the analysis. The HII/starburst galaxies show the
strongest deviations from smooth elliptical isophotes, while the normal
galaxies and LINERS have the least disturbed morphology. The Seyfert 2 galaxies
have significantly more twisted isophotes than any other category, and the
early-type Seyfert 2s are significantly more disturbed than the early-type
Seyfert 1s. The morphological differences between Seyfert 1s and 2s suggest
that more is at work than simply the viewing angle of the central engine. They
may correspond to different evolutionary stages.
