Searching for Fly-by Encounters of Galaxies in Cosmological Simulations

Sung-Ho An (Yonsei University)

Fly-by encounters of galaxies are believed to be far more frequent than direct mergers, playing an important role in galaxy evolution. Using cosmological N-body simulations, we have investigated the statistical properties of the fly-by interactions as functions of halo masses and ambient environments. We use a tree-particle-mesh code GOTPM, and discern impulsive fly-by pairs from eventual merger candidates based on the total energy of the two halos of interest. The results are summarized as follows: (1) Halos in the cluster environment experience more frequent mergers and fly-by encounters than those in the field region; (2) Both merger and fly-by fractions for the massive halos evolve more dramatically with time than those for dwarfs; and (3) The fly-by fraction decreases as approaching to z = 0, while the merger fraction increases.

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