The impact of environment on distant spiral galaxy evolution: velocity fields and Tully-Fisher relation of intermediate-redshift cluster galaxies; observations and numerical simulations
Final Report Abstract
Galaxy clusters play a fundamental role for the understanding of structure growth in the Universe. Besides the expected assembly of galaxies via mergers in the CDM theory, other interaction phenomena are important in the cluster environment (among galaxies but also hydrodynamic processes between the Intracluster Medium and the galaxy gas, and the influence of a cluster as a whole). To test the importance of these processes we studied the stellar populations (sizes, luminosities, morphologies) that heavily depend on the current star formation activity, but also the total gravitational potential via their internal kinematics which are influenced by both luminous and dark matter. We looked for tracers of possible interaction mechanisms of galaxies in 4 clusters at 0.3 < z < 0.6 by their signatures in structure (with our HST/ACS images) and in the full 2-dimensional velocity field (with our VLT 3D– spectroscopy). For the latter, we developed a new technique that allows efficient spatially resolved spectroscopy of distant galaxies. The velocity fields were analyzed with kinemetry and we conceived 3 quantitative parameters to examine irregularities. The distant galaxies were found to be more often disturbed than a local comparison sample. There is also a high percentage of distorted field galaxies, for which we postulate that we witness the ongoing growth of galaxy disks via accretion and minor merging. To disentangle the various interaction mechanisms and their importance for the evolution of the cluster population, we compared our observations directly with N-body/hydrodynamic simulations we performed both on galaxy scales and cluster scales. We followed the evolution of model galaxies undergoing fly-bys, merging, and ram-pressure stripping, and analyzed them in the same way as the observed ones thereby revealing distinct features for different processes. In addition, systematic effects from instrumentational constraints were examined with the simulations.
