Institute for Astro- and Particle Physics

Our institute is actively contributing to several large surveys, e.g. STAGES, the second largest mosaic ever observed with the Hubble Space Telescope. Here we study the evolution of thousands of galaxies in the environment of the galaxy supercluster Abell 901/902. The morphologies (shapes), sizes, stellar populations and many other parameters of the galaxies are analysed e.g. to understand why the mix of galaxy types has been different in earlier cosmic epochs than it is now. But not only the visible matter in this supercluster that extends over millions of light years, but also the dark matter is in our focus. Utilizing the so-called weak gravitational lensing effect, the spatial distribution of the dark matter has been derived with very high accuracy.

We also study the detailed evolution of disk galaxies  (like our own Galaxy) on time scales of billions of years, making extensive use of the worlds most powerful telescopes , e.g. the Very Large Telescope at Cerro Paranal, Chile, which is operated by the European Southern Observatory (ESO). In these studies we were able e.g. to derive the masses of the galaxies from the velocities with which they rotate. One of our most intriguing results is that visible and dark matter evolve in opposite ways. Dark matter evolves "hierarchically", with low-mass structures (so-called dark matter halos) forming first and high-mass structures forming last. But the stars (visible matter) form first inside the high-mass dark matter halos and only later inside the low-mass dark matter halos. This anti-hierarchical behaviour is still not very well understood.