Galaxy Mergers and Interactions at High Redshift

In this review we discuss the evidence for galaxy interactions and mergers in the distant universe and the role of mergers in forming galaxies. Observations show that the fraction of massive (M > M∗) galaxies involved in major mergers is roughly 5-10% at z ∼ 1. The merger fraction however increases steeply for the most massive galaxies up to z ∼ 3, where the merger fraction is 50±20%. Using N-body models of the galaxy merger process at a variety of merger conditions, merger mass ratios, and viewing angles this merger fraction can be converted into a merger rate, and mass accretion rate due to mergers. A simple integration of the merger rate shows that a typical massive galaxy at z ∼ 3 will undergo 4-5 major mergers between z ∼ 3 and z ∼ 0, with most of this activity, and resulting mass assembly, occurring at z > 1.5.