Institute for Astro- and Particle Physics

Galaxy clusters are the largest gravitationally bound systems in the universe. Besides all different types of galaxies they contain plasma, which emits radiation in the X-ray regime of the spectrum. This plasma is called Intra-Cluster Medium (ICM) and represents the major mass contribution to the baryonic mass content in these millions of light-years large structures. The mean temperature of the ICM is in the range of several million degrees and it has up to five times more mass than all galaxies in a galaxy cluster.
Since the first X-ray satellites it is evident that the ICM does contain higher order elements (e.g. Fe, Mg, O, Si, Ni), which are produced in the late evolutionary states of stars. The factories of heavy elements (stars) reside in the galaxies of a galaxy cluster, so the question arises: What are the mechanisms, that transport several 10³⁰ kg of mass per year into the ICM?

A researcher group at the Astro- and Particle Physics Institute models the formation and evolution of galaxy clusters in complex numerical simulations with a special emphasis on the transport mechanism. The results of the simulations can then be directly compared with X-ray observations of galaxy clusters.

With the help of these combined N-body/hydrodynamic high resolution galaxy cluster simulations and multi-wavelength observations the team was able to find out that the two main transport processes are galactic winds and ram-pressure stripping. Galactic winds are powered by supernova explosions of stars within cluster galaxies. These explosions accelerate the surrounding gas to escape velocities and mix the gas with heavy elements. Ram-Pressure Stripping is a passive transport mechanism. As galaxies move through the ICM, they feel the pressure of the ICM on their gas. In the inner parts of galaxy clusters the densities of the ICM and the relative velocities are so high that the galaxies start to peel away their outer gas layers, which contain processed gas with heavy elements.

With the help of the simulations the astrophysicists were able to study the strength and the time dependence of the two processes in detail. The lower right image gives an example of the results of such simulations. The temperature (red-orange colour map) and the iron nuclei distribution (blue isosurface) in a simulated galaxy cluster are shown. With the help of Mock observations of the simulated galaxy cluster the results can be directly compared with observations. This leads to a deep insight into the evolution and the interactions of the different processes in galaxy clusters.