Interactions and mergers at higher redshift
  In models of hierarchical structure formation, interactions and mergers at high redshift play a key role in the formation and evolution of galaxies. Numerical modeling and observations of nearby systems explore the detailed physics of galaxy interactions, but applying these results to the high redshift universe remains complicated. Evolution in the properties of galaxies over cosmic history may lead to differences in interaction-induced star formation as a function of redshift. High redshift interacting galaxies may be more prone to extreme, disk-wide starburst activity than are low redshift systems. Also, while activity in nearby clusters seems to be largely diminished, at higher redshift we observe galaxies falling into clusters for the first time. A variety of processes, including interactions and mergers, can drive strong evolution in cluster galaxies at higher redshift. 
Chris Mihos (Case Western Reserve University)