Frequency and impact of galaxy mergers and interactions over the last 7 Gyr

We explore the history and impact of galaxy mergers and interactions over z Ëœ 0.24-0.80, based on HST ACS, Combo-17, and Spitzer 24 mum data of Ëœ4500 galaxies in the GEMS survey. Using visual and quantitative parameters, we identify galaxies with strong distortions indicative of recent strong interactions and mergers versus normal galaxies (E/S0, Sa, Sb-Sc, Sd/Irr). Our preliminary results are: (1) The observed fraction F of strongly disturbed systems among high mass (M >= 2.5 × 10^{10} M_{o}) galaxies is Ëœ9% to 12% in every Gyr bin over zËœ0.24-0.80. The corresponding merger rate is Ëœ a few × 10^{-4} galaxies Gyr^{-1} Mpc^{-3}. The fraction F shows fair agreement with the merger fraction of mass ratio >= 1:10 predicted by several LambdaCDM-based simulations. (2) For M >= 1.0 × 10^{9} M_{o} systems, the average star formation rate (SFR) of strongly disturbed systems is only modestly enhanced with respect to normal galaxies. In fact, over z Ëœ 0.24-0.8, strongly disturbed systems only account for a small fraction (