Currently ongoing PhD projects

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

 
The Galactic Center cloud G2 as an outflow from a central star

The Galactic Center cloud G2 as an outflow from a central star

The gas and dust cloud G2 is orbiting around SgrA* on a very eccentric orbit and it has been passing pericenter in the early 2014 (Gillessen et al., 2012, 2013a,b, Pfuhl et al., 2015). Its discovery has triggered a large interest in the astronomical community, with several speculations on its fate, in its interaction with the hot surrounding gas and with the supermassive black hole in the Center of the Milky Way. However, the nature of G2 is still a matter of debate. In this PhD project, 2D and 3D AMR hydrodynamic simulations allowed us to test one specific scenario, namely G2 being the outflow from a central source (Ballone et al., 2013; in preparation; see also De Colle et al., 2014). This meant implementing the injection of gas in the simulation from an inner moving boundary on the best-fit observed orbit. A first set of simulations in 2D allowed us to study, with high resolution, the structure of such an outflow and to get an estimate of the parameters - namely the mass-loss rate and the velocity of the outflow -, needed to reproduce the observational properties of G2. The output values are compatible with those of a T Tauri star, as already suggested by Scoville $ Burkert (2013). Most recent simulations in 3D cartesian coordinates, using the AMR implementation of PLUTO, allow us a stricter comparison with the current IR observations, through the construction of mock position-velocity (PV) diagrams for the integral field spectrograph SINFONI at VLT.

Alessandro Ballone

 
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