Evolutionary Processes in Interacting Galaxies

The evolution of galaxy clusters is driven by various processes, which affect the cluster galaxies as well as the intra-cluster medium. In particular the interaction between (sub)clusters and the galaxies within them play an important role. Building on the results of our simulations and observations and using our unique, modular simulation code we plan to perform a quantitative analysis of the various interaction processes in particular with respect to metal enrichment. Particular emphasis will be put on two topics: (1) ram-pressure stripping - which has turned out to be a very common and efficient process - and (2) star formation - which is induced by various interaction processes. In addition we will perform calculations of non-thermal effects in connection with magnetic fields. We will refine and extend our method of calculating ``observed model clusters`` to even more observable parameters like e.g. different star formation indicators for direct comparison with observations. An important component of the programme will be multi-wavelengths observations for which Austria`s recent accession to ESO and our expertise in data analysis in multi-wavelengths puts us in a good situation. In addition to the use of existing facilities VLT, XMM, VLA, ATCA we prepare for upcoming facilities like ALMA and LOFAR.

The evolution of the largest bound structures in the universe clusters of galaxies is determined by various processes. These processes influence both the galaxies and the gas between the galaxies, the intra-cluster medium. Two aspects are of special importance: (1) stripping of galaxy gas: galaxies are moving with high velocity through the intra-cluster medium and feel the pressure of the intra-cluster medium similar to a headwind. When the pressure is high enough, it pushes the galaxy gas together and it is even partly stripped off. We were able to show that this stripping is a common phenomenon in galaxy clusters. Even in the outskirts of clusters it plays an important role. Its effects are distorted shapes of galaxies. Also the colours of galaxies are changing, when there is no or little gas present in the galaxies. The gas that has been stripped off, is mixing with the original intra-cluster medium and hence influences its composition. The other important aspect is star formation (2). New stars form in galaxies when gas is present. Various processes like e.g. the above mentioned external pressure or the approach of a second galaxy compress the gas and hence increase its density. In denser gas the probability to form star is considerably increased at least during the interaction. In the case that gas has been stripped off the probability decreases of course strongly. We were able to show that such kind of interaction processes happen often in galaxy clusters and that they can be detected in different ways. Of special relevance is the comparison of computer generated models with observations of real galaxy clusters in various wavelengths. In particular observations with ESO telescopes (European Southern Observatory) are important. While observations are only snapshots of clusters due to their long evolutionary times of billions of years, only computers can follow the evolution in a kind of fast forward mode. In order to get realistic model they always have to be compared with reality. A close connection of both research methods - observations and modelling - are therefore very advantageous.