Subgroup Prof. Michael Fellhauer
The Formation and Survival of Young Embedded Star Clusters:
The geometry of a young star forming region is usually not spherically symmetric as assumed in previous models but rather hierarchical in form of clumps and filaments. Our group models these more realistic initial conditions and investigates which effects govern the dynamics and which parameters are important for the survival (gas expulsion) of these SCs. With our simple models we can run hundreds of simulations and we obtain statistically relevant results.
We are also working on dynamical models to explain the slingshot mechanism, in which newborn stars get expelled from a single, oscillating filament. In this project we collaborate closely with the sub-group of Prof. Stutz.
In another new project together with the sub-group of Prof. Schleicher we investigate the formation of the very first star clusters and the influence of stellar collisions in these particular objects.
The Formation and Evolution of dSph Galaxies:
We investigate a new scenario for the formation of these faint dwarf galaxies. They are known to show features like distorted isophotes, off-centre nuclei or secondary density peaks. In our model we place dissolving star clusters (as we know: all stars form in SCs) inside the central area of a dark matter (DM) halo. The stars of the dissolving SCs are forming the faint luminous component of the dSph galaxy. Due to the fact that we are dealing with very low densities inside a very massive DM halo, our models reproduce all the features faint dSph galaxies.
We have now successfully implemented the different star formation histories of the dSph in our models. Furthermore, we are extending our models towards the regime of the ultra-faint dSph on one side and towards more massive dwarfs, which are rotationally supported on the other side.
project page 1
In terms of the evolution we have developed a new method to search for a best matching dark matter free progenitor and successfully applied this method for the ultra-faint dSph galaxies Ursa Minor II, Bootes, Hercules, Segue 1, Coma Berenice and Canes Venaticii I.
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The Formation and Evolution of Tidal Tails:
All objects (SCs and dSphs) orbiting the Milky Way (MW) are forming tidal tails. These tails align with time along the orbit and so it would be possible to deduce the orbit of the object from the location of the tails. Furthermore, these tails sometimes show density enhancements. In principle, having a large sample of tails, it should be possible to deduce the shape and strength of the MW potential from them. One needs a understanding of how certain parts of the MW (disc, bulge, halo) influence the tails and their over-densities. We are investigating how tails and their densities form in different environments and on different orbits and how they trace the Galactic potential. project page
Ultra-Compact Dwarf Galaxies (UCDs) Faint Fuzzies (FFs) and
compact Ellipticals (cEs):
We see that star formation happens not uniformly distributed but clustered in form of loose associations up to massive SC complexes (clusters of SC). Our group has developed a model to explain the formation of UCDs and FFs via the merging of SCs inside of SC complexes. Now we are extending these models to cEs. project page
- The importance of ram-pressure stripping and tidal harassment on dwarf galaxies, tidal dwarf galaxies and star cluster systems. Pre-processing of galaxies in the group environment before the infall into a galaxy cluster.
- Stellar dynamics in the MONDian context. Our group has
develloped one of the few N-body codes which can model MONDian
gravity -- RAyMOND.
We have furthermore deducted an extensive research if elliptical systems seen in the nearby Universe are explainable in the MONDian framework and assembled the largest catalogue of elliptical systems.
- We have researched the possibility of IMF variations (top or bottom heavy IMFs) in the context of UCDs and GCs.