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Currently ongoing PhD projects

 

Core fragmentation in filaments

Observations of the Herschel Space Observatory have shown that the sites of star-forming cores correlate with ubiquitous filamentary structures in molecular clouds. In order to develop a coherent model for star formation, it is essential to understand why and how filaments break up in cores. Several physical processes, such as external pressure, turbulence and magnetic fields, have been suggested to play a major role. Furthermore observations have revealed that supersonic filaments split up into subsonic, velocity coherent fibres. We use the grid code RAMSES to simulate fragmentation processes in filaments under different physical conditions and to develop models that can be used for future observations.

Stefan Heigl

Stellar Kinematics of Early-Type Galaxies

During the last decade, an extensive number of studies have been conducted investigating both the kinematic and the dynamic inner structure of early-type galaxies (ETGs). Within the ΛCDM paradigm galaxies grow in baryonic mass by early smooth accretion of cold gas, resulting in a triggering of insitu star formation. At lower redshifts, the growth is overwhelmingly driven by collisionless galactic mergers. While this two phase scenario represents a suitable picture of galaxy formation on cosmological timescales, the mechanisms determining the detailed inner structure of ETGs remain a matter of debate. Therefore we explore the connection between the stellar kinematical structure of ETGs and their respective formation pathways in a fully cosmological context utilising the hydrodynamic Magneticum Pathfinder simulations. Furthermore, we investigate the connection between the central stellar kinematics of ETGs and the kinematics of the stellar halo they reside in, since stellar halos encode valuable information about the formation of galaxies.

Felix Schulze

 

Orbital dynamics of galaxies in galaxy clusters

The effect of galactic orbits on a galaxy's internal evolution within a galaxy cluster environment has been the focus of heated debate in recent years. To disentangle this relationship, the velocity anisotropy, phase space and the orbital evolution of cluster satellites is investigated. Through the use of the hydrodynamic cosmological Magneticum Pathfinder simulations, we evaluate the orbits of subhalos associated with clusters from high redshift to the present. Through the inspection of different cluster masses and redshifts, we are able to achieve a diverse statistically relevant sample of subhalos inside clusters, which we further split into quiescent and star forming subhalos. This split allows us to observe the internal subhalo evolution and study its dependence on the velocity anisotropy parameter and the radial distance. 

Marcel Lotz

TAngular momentum properties of galaxies using the Magneticum Pathfinder simulations

Angular momentum properties of galaxies using the Magneticum Pathfinder simulations

We investigate the connection between the morphology and the angular momentum properties of galaxies using the Magneticum Pathfinder simulations. Furthermore, we test the dependency of the morphology on the environment. Finally, we will study the changes of galaxy/cluster properties in a ΛCDM universe including massive neutrinos as one of the DM components.

Adelheid Teklu

 
The engines of galaxies: towards a better understanding of active galactic nuclei

The engines of galaxies: towards a better understanding of active galactic nuclei

Almost every galaxy hosts a supermassive black hole. This black hole is located in the center of the galaxy and is fueled by in-falling gas, either from the galaxy itself or due to mergers with other galaxies or smaller substructures. Whether gas is accreted or not depends strongly on its properties such as the temperature or angular momentum. Only a fraction of the accreted matter leads to mass growth of the black hole, while the remaining energy is emitted by the black hole (AGN feedback) in the form of radiation and mechanical outflows (jets). In large cosmological simulations the gas properties and different types of AGN feedback are often neglected. To include such effects I develop sub-grid models and use the  Magneticum Pathfinder simulations at first to test the models and then to implement them in larger simulations. These simulations can be useful for making predictions i.e. for scaling relations between black holes and their host galaxies or to understand the clustering of AGN depending on their properties and environment. This can be used i.e. to estimate cluster masses from observables or to calibrate X-ray and SZ observables.

Lisa Steinborn

 
Origin and Properties of Giant Clumps in z=2 Disk Galaxies

Origin and Properties of Giant Clumps in z=2 Disk Galaxies

High resolution observations of disk galaxies at high-redshift e.g. with ESO's VLT reveal distinct differences when compared to present-day disk galaxies. Their structure is irregular with highly turbulent motions and high gas fractions of 30-80%. Stars form with enormous rates of a factor of 10-100 higher than in the Milky Way. The star formation is concentrated in a few gigantic clumps of molecular gas, about 1000 times larger than present day molecular clouds, and as big as dwarf galaxies. Numerical simulations of gravitationally unstable gas-rich disks show that fragmentation naturally leads to contracting and self-rotating clumps. However clear observational evidence for spinning clumps is still missing, which might either be caused by limited resolution or an alternative formation scenario. In order to gain a better understanding, we run idealized high resolution simulations of isolated gas-rich disks with the adaptive mesh refinement code RAMSES to follow the fragmentation process of gravitational instabilities from the beginning and the evolution up to a few orbital times. We also mock beam smearing effects to compare our results with observations.

Manuel Behrendt