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Finished Diploma/Master projects
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 confronting X-ray scaling relations. We analysed the relative contribution of XRB emission for a set of simulated galaxies of the Magneticum Pathfinder 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 Pathfinder 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).
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.
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.
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.
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
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.
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.
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.
Geray Karademir, 2018
Hydrodynamic Simulations of AGNs in Galaxy ClustersActive 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.
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.
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).
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.
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.
Emilio Mevius, 2016
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 â€zoom-inâ€ 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.
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.
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.
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.
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.
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.
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.
Max Brunner, 2012
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