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 ∼ 0.24–0.80, based on HST ACS, Combo-17, and Spitzer 24 μm data of ∼ 4500 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 M⊙) galaxies is ∼ 9% to 12% in every Gyr bin over z ∼ 0.24–0.80. The corresponding merger rate is ∼ a few ×10 galaxies Gyr Mpc. The fraction F shows fair agreement with the merger fraction of mass ratio ≥ 1:10 predicted by several LCDM-based simulations. (2) For M ≥ 1.0 × 10 M⊙ systems, the average SFR of strongly disturbed systems is only modestly enhanced with respect to normal galaxies. In fact, over z ∼ 0.24–0.8, strongly disturbed systems only account for a small fraction (< 30%) of the total SFR density. This suggest that the behaviour of the cosmic SFR density over z ∼ 0.24–0.80 is predominantly shaped by normal galaxies. University of Texas at Austin, Austin, TX 78712-0259 Max-Planck-Institut für Astronomie, Heidelberg, Germany The University of Nottingham, Nottingham NG7 2RD, UK Laboratoire d’Astrophysique, EPFL, 1290 Sauverny, Switzerland University of Innsbruck, A-6020 Innsbruck, Austria Johns Hopkins University, Baltimore, MD 21218 University of Texas, McDonald Observatory, Fort Davis TX, 79734 USA University of British Columbia, Vancouver, V6T 1Z1, Canada University of Massachusetts, Amherst, MA 01003, USA University of Arizona, Steward Observatory, Tucson, AZ 85721 NRC Herzberg Institute of Astrophysics, Victoria, Canada Centro Astronmico Hispano Alemn, Calar Alto, E-04004 Almeria, Spain Astrophysikalisches Institut Potsdam, D-14482 Potsdam, Germany University of Oxford, Keble Road, Oxford OX1 3RH, U.K. Institut d’Astrophysique de Paris, 75014 Paris, France