The role of galaxy-galaxy interactions in Galaxy evolution

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The nearby universe contains striking examples of galaxies which are interacting with one another. This process gravitationally disrupts one or both galaxies, and may result in a merger. At the same time, these close encounters can both trigger the formation of new generations of stars and (later) quench star formation in these galaxies. The study of interacting galaxies has greatly improved our understanding of these processes in recent years, though much remains to be learned. A crucial challenge is to relate the observations of these interacting galaxies to more typical (isolated) galaxies, which may nevertheless have undergone relatively recent interactions that have profoundly altered their evolutionary histories. The proposed research program will build on our recent contributions in this field, and will employ an extraordinary set of data and environmental classifications that we have assembled for this purpose. We have used this database to identify large numbers of galaxies in close pairs and compact groups, which provide ideal but distinct environments within which to detect ongoing, recent and imminent interactions. We will address our science goals by measuring a wide range of properties for galaxies in pairs and compact groups, by comparing these properties to galaxies in well defined control samples, by relating close pairs to wide pairs, and by relating compact group galaxies to those in their surroundings. With metrics such as the size-luminosity relation, the mass-metallicity relation, the colour-colour diagram, and star formation histories, we are poised to greatly improve our understanding of the role of interactions in galaxy evolution. Our existing samples of galaxy pairs and compact groups are unparalleled in terms of the number of galaxies, the quality and breadth of indices measured, the use of sophisticated control samples, and the ability to directly relate interacting galaxies to those which are not currently undergoing interactions. Moreover, we have the expertise in place to exploit these resources for many years to come, and to continue to involve postdocs, graduate students, and undergraduate students in this exciting collaborative endeavour.