Unveiling Galaxy Interactions: Watching the Tides Roll
  I set the stage for discussion of the stellar populations in interacting
galaxies by looking back over the slow development of our understanding of
these systems. From early anecdotal collections, to systematic cataloging, and
finally to increasingly sophisticated n-body calculations, we have seen how
gravity in distributed systems can produce the stunning variety of structures
we see. At the same time, measures across the spectrum have made it clear that
galaxy interactions are linked to star formation, albeit with the physical
mechanisms much less clear. Improved data sets, including HST imaging, deep IR
data, and large samples with well-defined selection criteria, have started to
reveal correlations with dynamical parameters pointing to detailed histories of
starbirth during collisions. The merger hypothesis for elliptical galaxies has
broadened into seeing interactions and mergers as important parts of the
overall evolution of galaxies. The connection becomes more important as we look
to higher redshift, where more frequent interactions can drive the evolution of
galaxies in multiple ways. Links between the properties of central black holes
and surrounding galaxies makes it important likewise to understand the
connections between AGN and interactions, which has remained more ambiguous due
to the strong role of sample selection. Finally, contemporary data reach deep
enough to show that most galaxies have interacted in the observable past; we
must consider these events to be a normal part of galaxy history.
