  Hubble Space Telescope images of the galaxies NGC 2207 and IC 2163 show star
formation and dust structures in a system that has experienced a recent grazing
encounter. Tidal forces from NGC 2207 compressed and elongated the disk of IC
2163, forming an oval ridge of star formation. Gas flowing away from this ridge
has thin parallel dust filaments transverse to the direction of motion.
Numerical models suggest that the filaments come from flocculent spiral arms
that were present before the interaction. A dust lane at the outer edge of the
tidal tail is a shock front where the flow abruptly changes direction. A spiral
arm of NGC 2207 that is backlit by IC 2163 is seen to contain several parallel,
knotty filaments that are probably shock fronts in a density wave. Blue
clusters of star formation inside these dust lanes show density wave triggering
by local gravitational collapse. Spiral arms inside the oval of IC 2163 could
be the result of ILR-related orbits in the tidal potential that formed the
oval. Their presence suggests that tidal forces alone may initiate a temporary
nuclear gas flow and eventual starburst without first forming a stellar bar.
Several emission structures resembling jets 100-1000 pc long appear. There is a
dense dark cloud with a conical shape 400 pc long and a bright compact cluster
at the tip, and with a conical emission nebula of the same length that points
away from the cluster in the other direction. This region coincides with a
non-thermal radio continuum source that is 1000 times the luminosity of Cas A
at 20 cm.
