The CFHTLS-Deep Catalog of Interacting Galaxies. I. Merger Rate Evolution to z = 1.2

We present the rest-frame optical galaxy merger fraction between 0.2 < z < 1.2, as a function of stellar mass and optical luminosity, as observed by the Canada-France-Hawaii Telescope Legacy Deep Survey (CFHTLS-Deep). We developed a new classification scheme to identify major galaxy-galaxy mergers based on the presence of tidal tails and bridges. These morphological features are signposts of recent and ongoing merger activity. Through the visual classification of all galaxies, down to i{sub vega} 4sigma level of confidence. A mild trend, where by massive galaxies with M{sub *}>10{sup 10.7} M{sub sun} are undergoing fewer mergers than less massive systems (M{sub *} approx 10{sup 10} M{sub sun}), consistent with the expectations of galaxy assembly downsizing is observed. Our results also show that interacting galaxies have on average SFRs double that found in non-interacting field galaxies. We conclude that (1) the optical galaxy merger fraction does evolve with redshift, (2) the merger fraction depends mildly on stellar mass, with lower mass galaxies having higher merger fractions at z < 1, and (3) star formation is triggered at all phases of a merger, with larger enhancements at later stages, consistent with N-body simulations.