  New optical and NIR K-band images of the inner 3 kpc region of the nearby
Virgo spiral M100 (NGC 4321) display remarkable morphological changes with
wavelength. While in the optical the light is dominated by a circumnuclear zone
of enhanced star formation, the features in the 2.2\mum image correspond to a
newly discovered kpc-size stellar bar, and a pair of leading arms situated
inside an ovally-shaped region. Only 5% of the K flux is emitted in
antisymmetric structures. This indicates that the morphology seen in the NIR is
dominated by a global density wave. Making a first-order correction for the
presence of localized dust extinction in K using the I-K image, we find that
the observed leading arm morphology is slightly hidden by dust. Possible
mechanisms responsible for the optical and NIR morphology are discussed, and
tests are proposed to discriminate between them. Conclusions are supported with
an evolutionary stellar population model reproducing the optical and NIR colors
in a number of star forming zones. We argue that this morphology is compatible
with the presence of a pair of inner Lindblad resonances in the region, and
show this explicitly in an accompanying paper by detailed numerical modeling.
The observed phenomena may provide insight into physical processes leading to
central activity in galaxies.
