Tracing Gas Properties in Merging Galaxy Clusters in Magneticum
The intracluster gas (ICM) in galaxy cluster experiences a lot of processes that change its temperature, density, velocity etc. For example, shockwaves created by the collision of the gas belonging to an infalling substructure and the gas of the main cluster or AGN feedback bubbles. These effects are recreated in cosmological, hydrodynamical n-body simulations like “Magneticum”. In this work gas, DM and star particles of an infalling substructure are traced to reveal the different behavior they exhibit during a merger. Gas slows down due to experienced pressure and mixes with the main cluster gas, while DM passes through the clusters core several times before it mixes. The gas temperature, density, entropy, and metallicity are recorded, showing that the gas experiences heating and compression during the infall, that can be interpreted as the gas being shocked. A shock front is found in radial profiles of temperature, from which the Mach number can be derived. The metallicity is increasing during the merger, but it can be noticed, that it is higher in the main cluster than in the infalling substructure, from which they could be distinguished.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.