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Finished Diploma/Master projects


Evolution and Dynamics of Cold Gas in Simulated Galaxies

Star formation in galaxies is fueled by their reservoirs of cold gas. In order to collapse into stars gas clouds need to cool effectively. Above temperatures of 10^4K the universally abundant atomic hydrogen is largely ionized and acts as an effective coolant. Below these temperatures however, other gas species have to fill this role. In this work an alternative implementation of cooling at these lower temperatures is tested in cosmological simulations with the OpenGadget3 SPH code. this implementation, developed by Dr. Umberto Maio, utilizes a chemical network to track the non-equilibrium abundances of the various hydrogen and helium molecules as well as the relevant states of select metal species for every SPH particle in the simulation. With this information the low temperature cooling contribution of these gas species can be computed at each timestep. The effect of this alternative implementation on galaxy formation and evolution is studied in re-simulations of Magneticum Box 4 and zoom-ins of two COMPASS regions. The abundance of molecular gas predicted by the model throughout the evolution of the universe is compared to observations. Different model configurations are tested to study the effectiveness of the hydrogen self-shielding implementation. The addition of density based self-shielding to the model is found to increase the cosmic abundance of molecular hydrogen in the simulation dramatically without drastically altering the evolution of galaxies in the cosmological box. However, the results also suggest that matching observed molecular gas abundances likely requires higher mass resolutions or further additions to the chemical network. A promising candidate for the latter solution is the implementation of dust as a catalyst for molecular hydrogen formation.

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Bendix Hagedorn, 2021


The Role of Physical and Numerical Viscosity in Hydrodynamical Instabilities

The evolution of the Kelvin-Helmholtz Instability (KHI) is widely used for testing numerical codes. We employ this instability in order to test both the smoothed particle hydrodynamics (SPH) and the meshless finite mass (MFM) codes implemented in OpenGadget3 and compare their accuracy in reproducing the KHI with different number of neighbours and different set-ups. Additionally, we also use the KHI to study the effect that a Braginskii viscosity has in the growth of the instability. We find a strong dependence on the number of neighbours in our SPH code, where with a low number of neighbours the instability is partially suppressed, but it can develop with a higher number of neighbours. The number of neighbours becomes also relevant depending on the initial conditions employed. This dependence is not found in the results with MFM, where the instability grows as expected independently on the number of neighbours and set-up employed. Physical viscosity plays an important role in the growth of the KHI, where we find a viscosity threshold that fully suppresses the instability. For viscosities smaller than this threshold the instability can develop, but the rate of growth depends on how viscous the fluids are. We also find that the intrinsic viscosity of the code contributes to the total amount of viscosity in the simulations, leading to a larger viscosity than the one implemented.

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Tirso Marin, 2021


Optimized Sampling of the Cooling Function for Cosmological Simulations Using an Amorphous Mesh

The so-called cooling function Λ is an important consideration in cosmological simulations. It depends on many different parameters, such as temperature, density, chemical composition, and radiation background, which makes it time consuming to calculate and introduces many features with large gradients to its functional form. As such, Λ is usually interpolated from regular grids of samples which provide only a poor approximation due to the high dimensionality of the parameter space. In this thesis a new sampling algorithm CHIPS is introduced, which draws samples using an amorphous mesh rather than a regular grid and automatically takes into account the shape of the cooling function to increase interpolation accuracy. Further, C/C++ implementation of a Delaunay based interpolation algorithm is developed to take advantage of these meshes and is integrated into the cosmological simulation codes OpenGadget and Gasoline. Results indicate that these new algorithms are superior to conventional methods in accuracy and speed, but suffer in memory use. These results are most pronounced in the low density regime, as well as near the hydrogen ionization threshold near 10^4K. Despite its drawbacks this approach shows promise and lays the groundwork for further research into mesh based interpolation of the cooling function.

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Stefan Lüders, 2021


Protoclusters of Galaxies in Cosmological Zoom Simulations

Scientific consensus has emerged around the influence of baryonic processes in protocluster evolution. Still, many questions remain open about the exact way and the extent to which energetic processes, like star formation, stellar feedback and AGN feedback, influence the evolution of galaxies and galaxy (proto)clusters. Using the new set of cosmological zoom simulations of galaxy clusters, called COMPASS, we study the morphology and formation history of 72 galaxy clusters. Performing simulations with varying subgrid physics, we isolate the effects of star formation, stellar evolution, metal treatment, supernova (SN) feedback and AGN feedback and compare our results for the simulated protoclusters and their galaxies with those derived from observations of high redshift protoclusters of similar mass. The analyses shows that independent of the subgrid physics implemented, the integrated star formation rate (SFR) at high redshifts of simulated protoclusters is approximately 4 times lower than the ones observed for protoclusters of similar total mass and integrated gas mass. Still, the simulated final cluster stellar mass produced is in concordance with low redshift observations. Interestingly, the implementation of a more complex metal treatment, SN feedback or AGN feedback, does not solve the observed discrepancy. We conclude that current simulations are unable to reproduce the bursty high redshift star production observed in protoclusters. Possible reasons for this discrepancy are either a numerical artifact related to resolution or the existence of additional physical processes responsible for triggering bursty star formation in protocluster galaxies.

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Elena Hernández Martínez, 2021


Shapes, Kinematics, and Formation Histories of Galaxies in Cosmological Simulations

As one of the most fundamental properties, the spatial distribution of matter is a key component for modeling galaxies and their dynamics. A good understanding of the 3D shapes of galaxies is therefore necessary. In this work, a variety of shape determination methods used in the literature are compared and tested. For the best method, the shapes of a sample of galaxies from Box4 (uhr) of the Magneticum Pathfinder Simulations are studied and related to the morphology, to kinematic and large-scale properties, and to properties describing the formation history. The analyses show that the shapes are correlated with a broad range of galaxy properties. Additionally, the radial shape and alignment profiles are analyzed for different kinematic classifications, where it is revealed how closely the dark matter (DM) follows the stellar component. This is an especially important result for the modeling of DM in galaxies, which is necessary for Jeans modeling, lensing models, and many other applications in astrophysics that try to connect the DM to the baryonic components to shed further light on the nature of DM.

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Lucas Valenzuela, 2021


Contribution from Stellar Binaries to the X-ray Emission of Simulated Galaxies

This work presentes the implementation of a new X-ray emission model for the stellar component of cosmological simulations in the form of X-ray binary emission within the framework of the virtual photon simulator Phox. The validity of the model is confirmed by reconstructing X-ray luminosity functions of local galaxies and con fronting X-ray scaling relations. We analysed the relative contribution of XRB emission for a set of simulated galaxies of the Magneticum Pathfi nder Simulation set over a broad range of energies, with respect to their ISM and AGN emission. Lastly, the X-ray emission within a lightcone view build from data of the Magneticum Pathfi nder simulation is compared with the unresolved cosmic X-ray background and in reasonable agreement for the power law behaviour in the hard X-ray band (E > 2 keV).

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Stephan Vladutescu-Zopp, 2021


Cosmic Rays in Galaxy Clusters - An on-the-fly Fokker-Planck Solver for OpenGadget3

High energy particles, mainly electrons and protons, make up a significant fraction of the interstellar- and a reasonable fraction of the intracluster medium. Observational evidence shows the existence of this component e.g. via synchrotron emission by relativistic electrons in spiral galaxies and in so-called “radio relics” on the outskirts of galaxy clusters. While recent work has been focusing more on this underrepresented component in structure formation simulations, most of this work has treated the energy budget of the Cosmic Ray (CR) component as a whole. Here we extended work started by Beata Pasternak to include CRs in our magneto-hydrodynamical simulations of structure formation, while also tracing the spectral evolution of CR populations. For this we included CRs as an additional fluid component and evolved the fluid by solving the diffusion-convection equation for CR population of electrons and protons. This was achieved by implementing a “Fokker-Planck-Solver” in OpenGadget3. The solver updates the spectra at every timestep according to adiabatic changes of the surrounding gas, radiative losses of the CRs, injection of CRs via “Diffuse Shock Acceleration” (DSA) and reacceleration of existing CRs due to turbulence of infalling substructure. We modelled the acceleration of CRs by shocks to a high accuracy and also find excellent agreement with analytic solutions for radiative cooling of electrons and the impact of adiabatic changes of the surrounding gas. Finally we used this model to run some preliminary simulations of idealized galaxy cluster mergers, which will give the basis for future work.

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Ludwig Böss, 2020

The Influence of Environment on the Stellar Kinematics of Brightest Cluster Galaxies

Brightest cluster galaxies, sitting in the gravitational centre of galaxy clusters, act as a link between galaxy and cluster physics. To what extend the stellar movement in galaxies is a product of their environment, is rather unclear. If cluster characteristics influence galaxy kinematics this effect should be most obvious in BCGs.

In this master thesis, I take an in-depth look at the kinematics of 398 BCGs from the Magneticum Pathfinder simulations. First, their kinematics are studied at z=0. Then 250 galaxies are traced to z=2. This allows to investigate the temporal evolution of many kinematical and environmental properties. The statistical evolution of these properties is examined and finally a case study of 12 BCGs is completed where the development of kinematics and environment is set in relation to one another. Six of these galaxies end up in a non-cool core environment whereas the cluster of four of these BCGs keeps its cool core.

The findings suggest that there is a correlation between coolcoreness and the h4 parameter. Furthermore, the development of a cool-core is a continuous process that correlates with strong mass accretion between 2 > z > 1.5 for the sample of 12 BCGs in this case study.

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  Maximilian Kühn, 2020


Implementing a Meshless-Finite-Mass Scheme Into the Cosmological N-Body Code Gadget

We implemented a meshless finite mass (MFM) scheme to resolve fluid dynamics in the cosmological N-body code OpenGadget3. In doing so, we offer an alternative method of simulating hydrodynamics in astrophysical environments, contrasted to the historic approach of smoothed particle hydrodynamics (SPH). The new scheme directly calculates inter-particle fluxes while still maintaining an overall Lagrangian nature. We discuss the theory behind both solvers and carry out various test cases to study their performances. We find that for simulations with exclusively hydrodynamical interactions, MFM produces less over-smoothing while executing in roughly half the time of SPH. This comes with the drawback of noisier solutions. Coupling our implementation to gravity, we see good agreement between SPH and MFM for simple tests but find numerical and physical instabilities for more demanding cases. We believe these to be resolvable without requiring a complete rewrite of the solver and expect MFM to become a viable competitor to SPH in the future.

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 Paul Hinz, 2020

Planes of Satellite Galaxies in Large-scale Cosmological Simulations

Recent observations have found highly anisotropic distributions of dwarf satellite galaxies around nearby central galaxies, most prominently Andromeda, the Milky Way, and Centaurus A. All three of the former have been observed to feature a thin, highly anisotropic and statistically significant plane of satellites, and the combined
odds for three similarly significant planes are negligible. Subsequent searches in cosmological simulations have led to mixed results, prompting our search in Magneticum.

In order to find explanations of this pronounced anisotropy, we explore three formation scenarios for such planes: group infall, second-generation tidal dwarfs, and filamentary accretion. Then we develop two methods of identification of satellite alignment and planes: the "three-satellite planes" method tries to locate preferential alignment through searches among all possible combinations involving three satellites of the respective central,
while the "momentum in thinnest plane" method fits the thinnest possible planes to subsets of the satellite population of a galaxy and then checks if their momentum adheres reasonably well to those planes.

The key results of our study are as follows: we find a pronounced preference for thin, momentum-aligned planes in the ensemble of our more than 600 systems. This trend is most visible in planes consisting of up to 50\% of the satellites available in the system, but also carries on into planes with a higher fraction of satellites partaking.
Further study is needed to quantitatively compare to other simulations and observations, but the results are nonetheless promising.

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Pascal Förster, 2019


The Interplay of Magnetic Fields and Star Formation Processes Using SPMHD Simulations

Cosmological simulations deal with very large structures and there is not enough resolution to couple all the dynamical range of processes taking place, so it is very important to model consistently phenomena that occur in unresolved scales. One example of subresolution model is proposed by [Springel and Hernquist, 2003] in which the star formation and the supernova feedback can be modeled by a multiphase structure of the Interstellar Medium (ISM). In their approach, the ISM consists of cold and hot gas and includes radiative heating, cooling, star formation and feedback from supernova. This model predicts a self-regulated star formation quiescent mode for the gaseous part of disk galaxies and has only one free parameter: the overall time-scale for star formation. First improvement of this model is to express the star formation rate in terms of external pressure, which allows to include further physical processes such as magnetic fields. This is done by assuming that the cold and hot phase of the ISM are in pressure equilibrium [Murante et al., 2010] and the star formation arises from the molecular fraction of the gas, which is proportional to external pressure [Blitz and Rosolowsky, 2006]. After implementing the MHD extension of the star formation model in gadget code [Springel, 2005, Springel et al., 2001] and having studied the behaviour of this model with simulations, we then can include a more complicated feedback model including magnetic field seeding from Supernova (SN) [Beck et al., 2013]. In particular, as it has already confirmed that the magnetic field in protogalaxies can be produced by the dynamo effect in contracting protostars [Bisnovatyi-Kogan et al., 1973]. Mass loss by stars and SN explosions can then enrich the ISM with magnetic fields and provide a seed field in the galactic dynamo. It is interesting to examine how this feedback model works with the MHD extension of the star formation model in idealized disk galaxies.

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Eirini Batziou, 2018


Spiral Galaxies in Cosmological Zoom-Simulations

Cosmological Zoom-Simulations have proven to be a invaluable tool to study structures on all scales, from superclusters down to large elliptical galaxies. With this study, we aim at resimulating Milky-Way-like disc galaxies and thereby to finalize an existing set of Zoom-Simulations which then spans a range in mass from 10^11 to 10^15 M⊙. To this end, we use a 1 Gpc/h sized cosmological box which allows to choose objects from a variety of cosmological ecosystems. For this purpose, significant improvements of the simulation setup are necessary. We revisit implementations of black hole merger processes, adapt the merger conditions, and conclude that black holes need to merge onto the black hole which resides deeper in the potential to assure the remnant black hole stays within the galaxy. A comprehensive parameter study of the AGN feedback model shows that best results are obtained if the feedback acts only on hot gas, regardless of the accretion mode of the AGN. Runs without AGN feedback do not result in realistic disc galaxies. Our final production runs yield galaxies which follow the relevant scaling relations. I emphasize the notably thin galactic discs and various morphological features in the galaxies, such as bars and spiral arms of different classes. The developed simulation setup allows diverse subsequent studies, which will benefit from even higher resolutions that are now feasible. Finally, I present the results of an observational study on spiral structure in disc galaxies and review the main features of an IFU data analysis pipeline, to complement the numerical investigations.

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Adrian Bittner, 2018


Simulated Galaxy Interactions In Cosmological and Idealized Environments

Most of all galaxies are not field galaxies but are companied by other galaxies in groups or clusters. A special case of these galaxy gatherings are compact galaxy groups, which are extremely dense accumulations of galaxies in which galaxy interactions occur very frequently. These interactions have a huge impact on the corresponding galaxies and are a fundamental part of galaxy evolution. The information about the merging events are stored in the outer stellar halo of a galaxy or in the intra group light (IGL) respectively. In this thesis cosmological zoom simulations of compact groups as well as a parameter study using high-resolution isolated galaxy merger simulations covering a large bandwidth of orbit parameters and mass-ratios were used to study the effects of galaxy interactions onto their evolution. During this study it is found that compact galaxy groups are physically dense objects, and indications were found for the final phase of compact groups to be giant elliptical galaxies in isolated environments. In addition it can be seen that mergers always deposit significant amounts of mass in the outer stellar halos of galaxies and are therefore building and contributing to the IGL. Furthermore is shown that the outer stellar halo is enriched mainly by minor and very minor mergers, while the morphology of galaxies is mainly influenced by major or intermediate mergers.

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Geray Karademir, 2018


Hydrodynamic Simulations of AGNs in Galaxy Clusters

Active galactic nuclei (AGN) are among the brightest objects in the universe and the least understood. They interact with their environment through several energy feedback mechanisms such as radiation, winds, and jets. Even though many details of these feedback processes are still to be worked out, it is certain that they strongly influence the evolutionary history of their host galaxy and galaxy clusters. Furthermore can AGNs hold the answers to open standing questions of observational measurements such as star formation rate quenching in galaxies and the cooling catastrophe of the intra-cluster medium.
In this work, the effects of AGNs on galaxy clusters were studied with the help of the TreePM-SPH-code GADGET-3. The main focus lies on the comparison of two AGN feedback routines, which have the treatment of the radio-mode as their
major difference. Since this is a preliminary study of concepts, low resolution simulations are used. Whereas the fiducial simulation implements the mechanical outflow, which dominates in the radio-mode, as thermal feedback, the new simulations impart kinetic energy. This is motivated through the closer agreement with a unified AGN model.

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Christoph Becker, 2017


Orbital Dynamics 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, we investigate the phase space, the orbital evolution and the velocity anisotropy of cluster satellites. Through the use of the hydrodynamic cosmological simulation Magneticum Pathfinder, we evaluate the orbits of subhalos associated with 20 clusters. Thus, we are able to achieve a statistically relevant sample of galaxies inside clusters, which we further split into quiescent and star forming galaxies. This split allows us to observe the internal galactic evolution and study its dependence on the radial distance and anisotropy parameter. We then extend our investigation and consider the evolution from high redshift to present day. This allows us, amongst other considerations, to relate infalling galaxies with their progenitors, so as to understand the star formation history. To evaluate the validity of the simulation-based findings, we compare, where possible, with observations. We find that at redshifts z < 0.5 the vast majority of galaxies are quenched through ram-pressure stripping during their first passage.

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Marcel Lotz, 2017


Modeling The Spectral Energy Distribution of Low Luminosity Active Galactic Nuclei

Feedback is a crucial ingredient to correctly predict galaxy evolution in cosmological simulations.Recent studies show that the most numerous class of AGNs in the local universe are low luminosity AGNs (LLAGNs), whose dominant energy output is likely carried by jets: collimated outflows of energetic particles, which could even exceed the feedback of supernovae.In contrast to the unified scheme for AGNs, where it is believed that around the black hole forms an accretion disc and further outside a torus, LLAGNs seem to show none of them. How then do the central engines receive energy? Which effects are triggering the launch of jets and provide their power? The ongoing processes seem to be fundamentally different to "normal" AGNs.

Despite the lack of knowledge about the full physical picture, a scaling relation of black holes over the entire mass-range is a starting point for developing numerical models; specifically in the case of LLAGNs models of jet-like outflows.In this thesis a semi-analytical numerical model, focusing on jet emission, is applied to a sample of three nearby LLAGNs, whose observational spectra consist out of highest angular resolution images available over nearly 10 orders of magnitude in frequency.For all sources the emission of a compact jet gives an excellent representation of the continuum emission over the entire spectrum.

Extending the number of objects investigated with this technique, will provide a better understanding of the radiative and kinetic energy output of LLAGNs.

This can be used in future cosmological simulations to improve the modelling of especially the late stage of galaxy evolution.

The panel displays the specific flux density (Jy) versus the frequency (Hz).
Black dots are the sub-arcsec resolution measurements. The X-ray data is indicated by the grey squares, their bars span one order of magnitude. Low angular resolution observations are represented by grey spikes.Grey diamonds display lower limits of core emission measurements.The coloured lines represent the spectrum of individual model components:

The thermal plasma at the base of the jet radiates synchrotron emission. The spectrum produced is the preshock component, represented by the dotted blue line.
Accelerated particles in the jet obey a power law energy distribution. Their synchrotron emission, the postshock component, is shown in dash-dotted green.
The energetic particles scatter up photons by the inverse Compton effect, giving rise to the Compton component (dash-dash-dotted cyan). The thermal spectrum of the truncated accretion disc is represented by the dashed red line. The model spectrum, the solid-thin black line, corresponds to the sum of all the components.

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Lennart Reb, 2017

Simulating Chemical Enrichment in Galaxies

The observed chemical enrichment can be used to constrain the feedback models used in numerical simulations for a wider understanding of galaxy formation and evolution. In this work is made an up to date comparison of the mass-metallicity relation (MZR) and the metallicity gradients from the latest observational data with galaxies in the Magneticum Pathfinder simulations, which follow a detailed model of stellar evolution and chemical enrichment, described in Tornatore et. all 2007. In addition, we try to mimic the same selection criteria made in observations within a galaxy, addressing the possible influence of observational and numerical issues in the discrepancies with observed trends.

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Emilio Mevius, 2016


The Kinematics of Elliptical Galaxies in The Magneticum Pathfinder Simulations

The formation and evolution of galaxies is still unknown in many aspects. The complex interplay between baryonic processes and the hierarchical structure formation of dark-matter halos is still a highly-debated research topic. Several recent studies using novel observational techniques, especially integral-field spectroscopy, suggest that the formation history, and thus the closely related in- and outflow of matter, is encoded in the stellar kinematics of galaxies. During the hierarchical assembly of dark-matter halos within the ΛCDM framework, dominant processes like stripping, harassment, and galactic mergers leave an imprint in the present-day kinematics of early-type galaxies (ETGs). Physical effects like dynamical friction and violent relaxation during these processes are capable of drastically modifying the statistical distribution of orbits, while triggered star-formation and accretion of fresh gas builds up new cold components.

In this study we explore the stellar kinematics of ETGs using the fully cosmological hydrodynamic Magneticum Pathfinder simulations. More specifically, we study the dichotomy of fast and slow rotating ETGs, first reported in the pioneering projects by SAURON and ATLAS3D. Applying different morphological tracers reveals that the two-dimensional density profile is not sufficient to disentangle fast and slow rotators. In contrast, the position in the stellar mass-angular momentum plane, which is a tracer for morphology, is strongly correlated with the kinematical flavour of an ETG. We compare, where possible, our results to recent observations to infer the formation history of those objects.

Furthermore, we study the misalignment angles between kinematics and morphology, defined as the angles between the total angular momentum and the principle axis of inertia to explore the complex interplay between angular momentum and morphology of ETGs.

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Felix Schulze, 2015

Modelling Warm Dark Matter in Cosmological Simulations

The standard ΛCDM model of cosmology postulates that the formation of structures in the universe is driven by a largely unknown component of dark matter. It is one of the most important projects of modern physics to find out what dark matter is. Cosmological simulations are an important tool to predict the effects of different dark matter models, and to constrain properties of dark matter by the comparison with observations of our universe. We attempt to simulate different warm dark matter scenarios in cosmological ”zoom-in” simulations (which allow the investigation of a single object in high resolution), and comsological boxes (which exhibit low resolution, but good statistics). However, N-Body simulations of warm dark matter suffer from the artificial fragmentation of filaments into small, spurious halos. We decide to address this problem by considering new numerical approaches. As a first approach we test Adaptive Gravitational Softening, but find that it does not help out, as it does not follow the anisotropic distortions of the dark matter sheet. Therefore, we develop the new numerical technique Anisotropic Softening which is based on the potential of ellipsoids that can deform and rotate along all three axes individually. The deformations of the ellipsoid are defined by the Geodesic Deviation Equation, a numerical technique that follows the distortions of an infinitesimal volume element around each particle (Vogelsberger et al., 2008). With Anisotropic Softening we manage to match mass- and force-resolution precisely also in situations of highly anisotropic collapse, and thereby avoid any artificial fragmentation while keeping the force resolution high. As a last step we present warm dark matter simulations in a full cosmological environment that do not suffer from any fragmentation.

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Jens Stücker, 2015


Angular Momentum Distribution in Galactic Halos

The evolution and distribution of the angular momentum (AM) of dark matter (DM) halos have been discussed in several studies over the past decades. To understand the connection between the AM of the DM halo and its galaxy, we extract in total more than 2,000 individual galaxies from the uhr run of Box4 of the Magneticum Pathfinder simulations at different redshifts. In these simulations we are able to split the galaxies into disk and speroidal systems. Our simulations reproduce well the observed scaling relations between the stellar mass and the stellar specific angular momentum. We find that disk galaxies preferentially reside in halos where the AM vector of the DM in the center is better aligned with the AM vector of the whole DM halo. The distribution of the spin parameter λ also shows a seperation of disk and speroidal galaxies.

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Adelheid Teklu, 2014


Black Holes in the Magneticum Pathfinder Simulations

Over the last years it has been generally accepted that black holes are essential to understand the formation and evolution of galaxies. But the detailed connection between the growth and evolution of black holes and their host galaxies as well as the observed, fundamental scaling relations between them are currently only poorly understood. In my thesis the Magneticum Pathfinder simulations are analysed quantitatively and qualitatively. Resolving galaxies and AGN feedback in cosmological simulations allows challenging the understanding of galaxy formation and its connection to black hole physics. In my thesis the reliability of the current black hole model is demonstrated by comparing the simulation with observations, i.e. the relation between the black hole mass and the stellar mass, the M-sigma-relation, the stellar mass functions or the luminosity functions at various redshifts. The simulations in general are very successful in reproducing these relations. Thus it is possible to investigate in detail how black holes grow, how their luminosity evolves over cosmic time and what their environment looks like. I could show that galaxy mergers play an important role for the black hole growth and thus for the appearance of AGN, which is depicted in the figure. The red dot represents the black hole, whereas cold gas is blue, hot gas is red and stars are white. The graphs below show the mass growth and the light curve of the black hole. The peak in the luminosity appears during a merger. I also found that fainter AGN can be triggered by mergers or smooth gas accretion. Furthermore I studied AGN feedback and black hole accretion in more detail. Thus the simulation could be improved by implementing a radiative efficiency of the AGN feedback, which depends on the black hole mass. I also showed that we have to improve the accretion model. In the simulations the Bondi model is used. The Bondi accretion rate is multiplied by a boost factor. Since the choice of this factor has a significant effect on the black hole growth we have to further understand the origin of this parameter.

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Lisa Bachmann, 2014


A Disk-Disk Major Merger Event in a Zoom-Simulation

With the aim to understand the formation of galaxies and especially the impact of the gas component and the feedback on the evolution of elliptical galaxies, we performed high-resolution zoom simulations of galaxies selected from a large cosmological box (Gpc in size), which are forming at the border or inside a void structure at present day (Magneticum Pathfinder simulations). The example on the left shows, within a self consistent cosmological context, the formation of a disk galaxy from a redshift of z=10 to z=0.45, where it suffers a major merging event with another massive disk galaxy. This causes a starburst and changes the morphology of the two galaxies that then form a single spheroidal galaxy. This is an event that can be seen in the present day universe, for example in the famous Mice Galaxies or the Antennae Galaxies. Our spheroidal galaxy undergoes another dynamical event during the last 2 Gyrs of its life until the present day that is also a major component of galaxy evolution: a massive dry minor merger. This merger leaves shell-like structures around the galaxy as a signature that is visible for about 200-500 Myrs, a phenomenon that can be observed at present day, for example in the Arp 227 Galaxy.

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David Schlachtenberger, 2014


On anisotropic thermal conduction in cluster cooling flows

Observations show that thermal conduction in cooling flows of galaxy clusters is strongly suppressed in some regions. This suppression is due to the restrictive motion of charged particles in a cluster's magnetic field. In this work we derive a numerical scheme to implemented anisotropic thermal conduction in the SPH code GADGET3, enhancing the existing isotropic formulation (Jubelgas et al. 2004). We present several approaches to handle this task and discuss the outcome using test cases as well as cluster simulations.

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Alexander Arth, 2013


Functional Methods to Set Up and Analyze Hydrodynamical Simulations of Star-Forming Molecular Clouds

The thesis applies modern programming techniques to simulations of star-forming molecular clouds. It is composed of three parts: first, methods to efficiently set up, export, start, and analyze runs of a Smoothed Particle Hydrodynamics (SPH) simulation, using the Espresso simulator. Second, simulations of the radial density distribution of isothermal star-forming filaments using a custom one-dimensional grid simulator with cylindrical symmetry. And third, an assessment of the F# programming language, Common Language Infrastructure (CLI) and the functional programming paradigm in general for use in physical applications.

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Georg Michna, 2013


Self-regulated Star Formation in Galactic Disks, Influenced by the Accretion of Cosmic Gas

Developing and testing numerical methods to examine the appearance of a self-regulated equilibrium state in spiral disk galaxies, where the star formation rate follows the accretion rate of extragalactic gas.

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Max Brunner, 2012

Giant Clumps in High-Redshift Disk Galaxies

Giant Clumps in High-Redshift Disk Galaxies

(i) Developing the required observations and theory. (ii) Setup of stable/unstable gas disks, embedded in a spherical dark matter halo, by using the grid-code RAMSES. (iii) Analyzing of the disk transformation and the developed clumps.

Manuel Behrendt, 2011




Finished Bachelor projects


Shocks and Corresponding Physical Properties of Merging Galaxy Clusters in Magneticum

The process of merging galaxy clusters leads to several interesting physical circumstances. As a consequence of the compression of the intracluster medium, shock waves originate due to the infalling galaxy subclusters towards their potential minimum. The effects of cluster mergers, simulated by the cosmological, hydrodynamic, n-body simulation "Magneticum", were used for further analysis. In this work a closer look was taken into the presence of X-rays and the Sunyaev-Zeldovich Effect in conjunction with the appearance of shocks. More precisely: The displacement of their radiation centroids in comparison to the center of gravity of the most massive subcluster under the condition, that shocks have been detected. The main goal was to find out, whether these X-ray and SZ centroid offsets relate in distance and distribution to the appearance of shock waves in merging galaxy clusters.

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Julian Sommer, 2021


Cored and Low Density Halos

In this thesis, I analyzed the inner density of the dark matter halos in the Magneticum simulations and compared it with the conclusions in the observations from Genzel et al. 2020. They propose that cores form at high redshift by expanding their inner dark matter content, which results in a low inner dark matter surface density. The simulation data indicates that cores form at low redshift without altering the inner dark matter surface density in a relevant manner, contradictory to Genzel et al. (2020). Halos with a low inner dark matter surface density do also not show a tendency towards flat distributions.

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Sebastian Langer, 2020


Computer vs. Telescope – Comparison of Measurements of Metallicity with Simulations and Observations

In this thesis I looked at different ways of measurements of metallicity in galaxies. The main goal was to find out whether the results of the MAGNETICUM simulation match the ones of observations. The thesis focuses on the so called metallicity gradients within a galaxy and the mass metallicity relation. It also contains a comparison of the three simulations EAGLE, ILLUSTRIS and MAGNETICUM. I find that the results of the simulations lead to very similar results as the observations.

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Franziska Eisner, 2019


Properties of Magneticum Disk Galaxies in the Context of Modified Newtonian Dynamics

MOdified Newtonian Dynamics (MOND) proposes an alteration of Newton‘s second law to explain the internal dynamics of galaxies. The addition of a term dependent on acceleration is supposed to give an alternative explanation - besides the standard idea of Dark Matter (DM) - of phenomena like flat rotation curves. Due to the nature of the theory, MOND predicts specific scaling relations between the observed acceleration and the one provided by baryonic matter with Newtonian physics at any point. The detection of this scaling in nature has prompted investigation into the existence of similar relations in cosmological simulations using the standard model including DM. This thesis takes a close look at the dynamics of galaxies in the Magneticum simulation, with the conclusion that many predictions of MOND are indeed reproduced, down to the occurrence of such acceleration-relations in individual galaxies.

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Alexander Mayer, 2019


The Influence of The UV-Background on The Cooling of Gases

This thesis examines the effects of different Ultraviolet Backgrounds (UVBs) on gas cooling at low densities. Using the photoionization software Cloudy, the UVBs of Haardt & Madau 2005, Haardt & Madau 2012, Faucher-Giguère 2011 and Khaire & Srianand are compared, accounting for redshift, metallicity and hydrogen density. Python scripts to reproduce and visualize the data are provided.

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Stefan Lueders, 2018


Radial Orbit Instability - Analysis of geometry in unperturbed and perturbed systems

Radial Orbit Instability (ROI) has long been a matter of interest for the dynamic evolution of stellar systems. While it was mostly discussed as a form of instability in globular clusters and elliptical galaxies, recent studies have extended the theory to be applicable to dark matter halos.

This thesis studies the intrinsic geometry of collisionless stellar systems that underwent ROI. First an energy-threshold for the onset of ROI in terms of the virial ratio was derived from numerous n-body simulations. The second half of the thesis studies the impact of perturbations, in the form of added rotational velocity or a compact central mass, on the development of the instability and the resulting geometric properties.

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Ludwig Boess, 2018


Cool Core Clusters in the Magneticum Pathfinder Simulation

The nomenclature Cool Core (CC) or Non-Cool Core (NCC) Cluster is used to classify clusters according to their different thermodynamical properties of the Intra-Cluster Medium (ICM). Cool Core Cluster show short central cooling times, low central entropies, temperature drops towards their centers and high central electron number densities. Non-Cool Core Clusters lack of these properties and thus reveal longer central cooling times, higher central entropies and lower central electron number densities. Observations of cluster samples have revealed that CC and NCC clusters are nearly equally distributed with a slight trend towards a higher NCC frequency. In this thesis, the fraction of CC and NCC clusters in the Magneticum Pathfinder Simulation is investigated and further thermodynamical properties of the ICM are examined using the classification of CC and NCC clusters.

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Jennifer Hinz, 2018


Probing The Richness Mass Proxy with Magneticum Simulation Galaxy Clusters

In this thesis we compare five different mass proxies of nearby galaxy clusters: The x-ray luminosity, the temperature, the Sunyaev-Zel'dovich effect, the velocity dispersion and the richness. We mainly focus on the representation of richness in the Magneticum simulation, since it is the mainly only observational constrain. For this purpose we calculate mass-effect relations from the simulation and compare it to the data from various observations. In a later step we examine more accurately the mass-luminosity relation by taking more physical processes into account. We evaluate the changes of the mass from both methods.

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Maximilian Kuehn, 2017


Magneticum Superclusters

Superclusters are the largest density enhancements in our Universe. In this bachelor thesis i worked to find superclusters inside the magneticum boxes 0 and 2b. All results are shown in different plots. Superclusters are found by searching for bound structures. Therefor it is important to calculate the potential, the kinetic energy and the hubble-expansion of the universe. The results are compared with those from the REFLEX-II survey concerning multiplicity and extend of the superclusters. The picture shows superclusters inside box 0 consisting of minimum 3 members.

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Andreas Hofmann, 2017

Turbulence in SPH

Turbulence in SPH

The thesis at hand has been prompted by recent publications about the "natural" limitations of smoothed particle hydrodynamics (SPH) with regard to the simulation of turbulence. These findings center around unwanted side effects of artificial viscosity, which needs to be introduced into the otherwise perfectly Lagrangian scheme to implement dissipation. Most prominent in that regard is the paper by Bauer and Springel (2012) about deficits in the subsonic turbulent regime, which dissuades further use of SPH codes in the regime and suggests the use of moving-mesh codes like Arepo. Although a well-considered answer to that specific paper already exists in form of Price (2012), the idea had been shown to assess our current SPH code Gadget-3 equipped with state-of-the-art schemes and compare it to matching Arepo runs. To that end we performed various turbulent simulations with both Gadget-3 and Arepo. Besides the results and analysis of these simulations, this thesis contains a concise introduction to hydrodynamics as well as to the principles of the theory of turbulence, complemented by the basic concepts of smoothed particle hydrodynamics simulations. The thesis also features an extensive appendix with most of the source code. 

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Pascal Förster, 2014


Simulating Stephan's Quintet

N-Body/SPMHD Simulation of Stephan's Quintet

Based on previous studies we perform further N-Body- and SPMHD-Simulations with the code /GADGET/ on the history of Stephan's Quintet. We hereby tested different models concerning the angles of the galaxy discs and adapted masses of the original galaxies. We found well formed characteristical tails in the south-east in both models. It becomes apparent that the correction of the angles does have an influence on the outcome and especially on the detailed development of the tails. Additionaly we used the code Splotch to generate movies and appealing visualisiations of the performed simulations that illustrate the initial conditions as well as the activities during the interactions between the galaxies.

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Michael Hartmann, 2013


The Galactic
  Centre cloud G2 and scattering processes in the young stellar ring

The Galactic Centre cloud G2 and scattering processes in the young stellar ring

The origin and nature of the Galactic Centre cloud G2 is still a matter of investigation. Of special interest here was the so-called 'Compact Source Scenario' assuming a low-mass star as source for the observed cloud which could have been scattered by massive stars of the young stellar ring to its highly eccentric orbit around the black hole. In this bachelor thesis I focused on the question of the likelihood for a low-mass star originating from the young disk to be scattered on a G2-like orbit. For this, I made a rough analytical approach on the delivery rates on highly eccentric orbits by one single scattering event. As a comparison I run several N-body simulations which imitate the evolution of the orbits in the young stellar ring during its estimated lifetime of 6 Myr.

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Miriam Keppler, 2013


G2 cloud evolution

Investigation of the gas cloud G2 in the Galactic Centre

Recently, a gas cloud has been discovered with approximately three times the mass of the earth in the Galactic Centre. It is on a highly eccentric orbit around the supermassive black hole. The cloud named G2 reaches the pericentre radius of 36 light hours in summer 2013. Because of the gravitational force of the black hole the cloud is tidally disrupted. In my bachelor thesis I created a simulation using C++ for a simple scenario, where the gravitation dominates. Every other influence is neglected. Several simulations have been done before and the conclusion was that because of the disruption G2 formed most likely in 1995. But there is no mass that could form a cloud. So I started the simulation in 1944, in the apocentre, because there is a good enviroment for forming such a cloud. My simulations show that there is a possibility that G2 was formed in 1944. In that case the initial radius of the cloud and its mass are much smaller than assumed.

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Norbert Konrad, 2013


Spiral galaxies in cosmological simulations

Spiral galaxies in cosmological simulations

In recent studies of galaxy formation in cosmological simulations a angular momentum problem occurred leading to more compact disks compared to observations. Hence in this bachelor thesis we investigated some properties of disk galaxies, produced by the hydrodynamical cosmological simulation Magneticum, like morphology or rotation curves and compared our results with present studies and observations. Furthermore we studied how a extended gas disk formed at z=1.4. In conclusion we use a self developed method to characterize gas disks inside dark matter halos to investigate occurrence and position of disks within the simulated box.

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Felix Schulze, 2012


Angular momentum profiles of dark matter halos

Angular momentum profiles of dark matter halos

According to the standard theory of the formation of galactic discs within extended dark matter halos the angular momentum distribution (AMD) of the gas component initially mirros that of the dark material. Therefore in this picture the angular momentum profile of a galactic disc can be extracted from the profile of its halo host, once the latter is known. In this work we study the angular momentum profiles of a sample of dark matter halos drawn from the hydrodynamical cosmological simulation Magneticum. We investigate in detail the cumulative mass distribution of angular momentum and statistical properties of the AMDs of dark halos. Furthermore we analyse the AMDs of halos from various non-cosmological simulations. Finally we characterize the spatial distribution of angular momentum inside halos and compare several parameters of the AMDs of dark halos and galactic discs.

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Torben Erik Simm, 2012


Evolution of BHs in the centers of galaxies

Evolution of black holes in the centers of galaxies

In this bachelor thesis the evolution of black holes in the centre of galaxies was investigated especially concerning the temporal development of their accretion rates and their masses for different redshift intervals between z=6.8 and z=0.0 depending on the used simulation. It managed to point out a characteristic evolution of the black holes by the consideration of simulated findings. In order to test the conclusions drawn by analysing simulated findings, comparisons of observational and simulated data concerning the accretion rates and masses as well as concerning the luminosity function were done.

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Lucas Sommer, 2012


Cold streams in high-z galaxies

Cold streams in high-z galaxies

Halos at redshift z > 2 are thought to be fed by streams of cold gas, which leads to a high starformation rate at these redshifts. Hence, in this work we investigate several physical properties of halos with about 1012 solar masses from a hydrodynamical cosmological simulation at redshfit z = 2.33 and study how these properties evolve with time. In particular we focus on the different behavior of the hot and cold gas components. 

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Adelheid Teklu, 2012


S-Stars in the Galactic Centre

On the Formation of the S-Stars in the Galactic Centre

In my bachelor thesis I tested a theory about the origin of the S-Stars around the central supermassive black hole (SMBH) in the center of our Milky Way: Infalling gas clouds gravitationally influence a test star situated in a distance of about 0.1 to 0.5 parsec from the SMBH with the result that it's orbit is bound much closer to the black hole than before. For this tests I wrote numerical simulation programs to simulate these 3-body-scenarios over a wide range for parameters like infall direction of the cloud, its speed and the orientation of the test star orbit in relation to the cloud.

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Christian Franik, 2011


Dynamics of the Milky Way - Andromeda System

Dynamics of the Milky Way - Andromeda System

In my bachelor thesis I should calculate the time of the possible collision between the Milky Way and the Andromeda-Galaxy. Therefore I created a program using Fortran, that computed the velocity and the position of the two big galaxys only under the influence of the gravitation force between them. I used the Leapfrog-method, which is more exact than the Euler algorithm, because it calculates position and velocity at different time-steps. The result was that the possible merger of Milky Way and Andromeda starts in 2 - 3 billion years. In the picture you can see the time until the two galaxies begin zu merge. The red line is the velocity of Milky Way and the green one that of Andromeda. The two horizontal lines represent the actual difference of the velocities of Milky Way and Andromeda. So the collision takes place in about 2 Gyr. 

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Sheila Hieber, 2011


Massflow in cosmic filaments

Massflow in cosmic filaments

In my bachelor thesis I studied the flow of gas and dark matter in cosmic filaments. The initial point was a simulated protocluster at z = 2, performed by the GADGET 2 code. The first step was to approximate the curved filaments with cylinders. In a next step I calculated the parallel und perpendicular component of velocity and massflow. In cosmic filaments matter is first accreted to the central region of the filament where it then streams to the central galaxy cluster. The flow of the gas component is strongly dependent on temperature.

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Klaus Jakabos, 2011


Filamentary Bubbles

Filamentary structure of wind blown superbubbles

In my thesis I studied the fractal character of a simulation of two wind-blown superbubbles colliding in the interstellar medium. Molecular hydrogen is blown away from two new born stars. At the meeting point the gas shows a more and more fragmental shape. The fractal dimension was calculated via the box counting method for different thresholds of hydrogen density as well as for different time steps after star formation. Plots of different timesteps and hydrogen thresholds as well as corresponding results for the fractal dimension are shown. The fractal dimension as a function of the density threshold can also be seen. 

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Birgitta Müller, 2011


The influence of central supermassive black holes on major
  merger remnants

The influence of central supermassive black holes on major merger remnants



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David Schlachtenberger, 2011