"Formation & Evolution of Galaxies"

The main scope of the new chair for extragalactic astrophysics and cosmology is to explore and understand the formation of galaxies and their evolution in different environments. We have now good evidence that within the first 1 billion years after the Big Bang, the first population of stars emerged out of the initial pool of particles and assembled in large systems – the galaxies. However, the details of the origins of stars and galaxies and how they have evolved over the subsequent 12 billion years until today are largely unknown. Our research contributes to understand these fundamental issues by investigating mass assembly, star formation, and galaxy interactions.

The majority of our studies is based on quantitative observations of very distant galaxies that appear small and dim even through the biggest telescopes. Since the more distant the observed galaxies are, the more we look back in time, we, thus, assess the objects when they were much younger than today. The measured physical properties probe the evolutionary status at different cosmological epochs so that we directly determine galaxy evolution and provide strong constraints on galaxy formation models.

Galaxies can interact with other objects during their cosmic evolution with the rate of such interactions strongly depending on the environment, that is the space density of galaxy neighbours. One important aspect of our work is, therefore, to observe a large number of galaxies not only in the field but also in groups and clusters of galaxies. There is a whole variety of processes that affect the stellar populations and alter galaxy evolution; even structural transformations changing the overall shape are observed. Our studies investigate the impact of such mechanisms like merging and tidal harassment on a stellar system, and the efficiency of hydrodynamic interactions between interstellar gas and the hot plasma medium in clusters. In order to reveal more details of such events, some of our projects focus also on nearby objects in the local Universe.

For our quantitative observations we mainly utilize the new generation of ground-based 10m-class telescopes (like the Very Large Telescope of the European Southern Observatory) that allows us to conduct spectroscopy even of the faint and small very distant galaxies. The spectra reveal the internal kinematics of the galaxies (i.e. the motion of all the stars within a respective galaxy), from which their mass can be derived, the properties of their stellar populations, and their chemistry. Complementary to the terrestrial observatories, we also conduct observations with satellites like the Hubble Space Telescope that enables us to spatially resolve the small galaxies to measure their sizes and shape (morphology). With the new and powerful instruments we are able to quantitatively explore the light and mass evolution of galaxies over cosmological timescales.