Thesis Projects

The Origin of Magnetic Fields and Multi Messenger Particles in the Local Universe

Magnetic fields and relativistic particles - cosmic rays - are the fundamental non-thermal components of the visible Universe. However, our understanding about the origin, distribution and amplification of magnetic fields as well as the acceleration and propagation of high energetic cosmic rays are still largely unexplored. Using a new generation of constrained simulations will allow constraining models of the origin of the magnetic fields as well as the origin of the observed ultra high energy cosmic rays (UHECRs). Modeling the propagation of such multi messenger particles like Neutrinos, gamma rays and UHECRs through various realizations of the simulated counterpart of the Local Universe to predict the observational signal at Earth will allow to simultaneously impose constrains on the distribution of sources for UHECRs and therefore their origin as well as possible origins of cosmological magnetic fields. In the initial phase of project, we will develop and run various realizations of the Local Universe employing various different seed mechanisms (primordial, supernovae and black hole based) for magnetic fields, while in the second phase these models will be explored for UHECR propagation.

Johannes Stoiber

Collecting Shells in the Tides: Formation of Dwarf Galaxies From Mergers Inside Galaxy Clusters

Although galaxy interactions are thought to provide a possible cradle for low-mass objects, environmental influence could still be a crucial driver for their formation and evolution. This hypothesis is stimulated by observations of star forming knots inside extended tidal tails of ongoing galaxy mergers in clusters. Such an arrangement prompts the intriguing question as to whether cluster environments could support tidal dwarf formation. I test this evolutionary channel by performing hydrodynamical simulations of galaxy mergers inside clusters. I demonstrate that environments indeed are capable of stripping tidal dwarf galaxies. Exposed to ram pressure, these gas dominated objects exhibit high star formation rates, while also loosing gas at the high-mass end. With time, they either evaporate due to their low initial mass, or are disrupted as soon as they reach the cluster center. Intact dwarf galaxies can still be found ~4 Gyr after the merger event, demonstrating that such objects can prevail for a significant portion of the Hubble time. The obtained results indicate that the fraction of dwarf galaxies with tidal origin could be significantly higher than in current estimates adopted in the literature, since the latter do not consider environmentally supported formation scenarios.

Anna Ivleva

Properties of Galaxy Clusters and their Galaxy Populations over Cosmic Time

Understanding the formation and evolution of the largest nodes in the cosmic web, so-called galaxy clusters, from their protocluster stages to their present-day properties, as well as the detailed evolution of the galaxies within such clusters, is the aim of this PhD Thesis. To achieve this goal, I perform extremely high resolved hydrodynamical simulations of galaxy clusters with present-day masses above . This not only allows to study the galaxy cluster properties such as their relaxation stages, substructure properties, and growth phases through the cosmic web accretion, but also provides highly resolved galaxies. For these galaxies, cluster-intrinsic effects like ram-pressure stripping can be studied in detail, as well as the formation and properties of special galaxy classes like ultra-diffuse galaxies.

Lucas Kimmig

LOCALIZATION: Constrained Local Universe Simulations

I work on the production of the largest constrained simulations of our local Universe. The aim of the project is to search, in the local matter distribution, for an answer to both the σ8 tension and the CMB anomalies observed in the Planck data, by performing a comprehensive analysis of local galaxy clusters and Large-Scale Structure (LSS) and of their impact on the CMB.

Elena Hernandez

Simulations of Supernovae in a Stratified, Shearing Interstellar Medium

Supernovae (SNe) are believed to play an important role in the regulation of star formation on galactic scales, as they heat up and disrupt collapsing clouds preventing them from any subsequent star formation.

Furthermore, they inject heavy elements forming in the center of massive stars into the interstellar medium, enabling the synthesis of complex molecules and dust grains, which are the basic ingredients for planet formation and life.

In recent years, the immediate importance of SNe for life on earth and the solar system has been further solidified, by mineral records of heavy elements found in sediments on earth, indicating that in the past few Million years the solar system must have interacted with nearby SNe.

Indeed, recent observations with GAIA show, that the solar system is currently located in the center of a large region of hot gas known as the "Local Bubble", which may have formed as the result of roughly 14 SNe over the past 15 Million years.

In this thesis, we aim to advance our understanding of SNe, by studying their dynamics in a stratified, shearing environment analogous to the solar neighborhood.

To this end we utilize the adaptive mesh refinement hydrodynamics code RAMSES, for simulations of SNe, embedded in a Milky-Way-like galaxy at high resolution.

Leonard Romano

Full Spectral Analysis of Star-Forming Galaxies

The high-quality spectra of the latest galactic surveys contain versatile information about the physical properties of the captured galaxies, such as stellar mass, metallicity, current star-formation rate and star-formation history (SFH).

Due to the complexity of the system, the full spectral analysis of star-forming galaxies is still a challenging but worthwhile task. One popular method of stellar population synthesis infers the total galaxy spectrum as a linear combination of single-burst models with no constraints on the star-formation history. These spectral buildings blocks, called single stellar populations (SSPs), are a joint result from stellar evolution in the HRD, stellar spectral libraries and a stellar initial mass function.

Combined with modern fitting-algorithms this approach makes it possible to translate the measured galactic spectrum into a discretized approximation of its SFH and chemical evolution history (CEH).

Although or precisely because of conceptual and numerical improvements in the last years, it is crucial to understand the limitations, uncertainties and approximations in stellar population modelling in general. Only then, spatially-resolved spectra galaxy- spectra from new generations of integral field spectroscopy (IFS) surveys can be properly investigated. This opens up new ways of studying specific target galaxies in unmatched accuracy and unveil their exciting past.

Eva Sextl

Energy balance in cool core galaxy clusters: The interplay of gravitational collapse and AGN feedback in a cosmological background

The standard picture of the cooling flow problem resorts to AGN feedback to balance the radiative losses due to X-Ray emission with either thermal or kinetic feedback. However the current prescriptions to implement AGN feedback in cosmological simulations exhibit a fine tuning problem to balance radiative losses with AGN feedback, resulting typically in an excess of feedback, and difficulties distributing the injected energy smoothly in the whole extent of the core region. In this context we aim to study all contributions to the energy balance in the core region of galaxy clusters, including not only radiative losses and AGN feedback, but also thermal conductivity, gravitational compression, and the effect of the background cosmological expansion.

Justo Gonzalez

AGN evolution processes: black hole spin, accretion and feedback in multi-scale hydrodynamical simulations

The main aim of the PhD project will be to gain insight into super-massive black hole fuelling and feedback processes as well as AGN activity and examine their role in the evolution of their host galaxies and cluster environment. I will develop and implement new sub-resolution models that take into account how gas accretion from large scales affects the black hole spin evolution — in magnitude and direction — when it is mediated by the presence of an accretion disk, as well as include a prescription for a large-scale jet, and its relation with the black hole spin. A key point will also be the estimation of the uncertainties related to sub-grid models.

Luca Sala

Deciphering Galaxy Kinematics and Dynamics Through Tracer Populations in Simulations and Observations

To investigate the kinematics in galaxies, especially bright objects can be used as tracers, in particular in the outer regions where the stellar light is dimmer and therefore more difficult to observe. Both globular clusters (GCs) and planetary nebulae (PNe; because of their bright [OIII] line) have commonly been used for this. The aim of this PhD project is to implement GC sink particles in OpenGadget3 to self-consistently form and evolve GCs in COMPASS, a suite of cosmological zoom simulations, and to model PNe in the Magneticum Pathfinder cosmological simulations in post-processing. This will be used to study what these tracer populations encode about a galaxy's present-day properties and formation history. Additionally, the GC model will allow investigating GC formation and the PNe model will be used to study the planetary nebulae luminosity function (PNLF), both of which are still poorly understood.

Lucas Valenzuela

Decomposition of galactic X-ray spectra using PHOX

During the past years, X-ray observations of galaxies and galaxy clusters proved to be a powerful tool to study the assembly of baryonic matter into large structures. With the new possibilities achievable with current and upcoming X-ray missions (e.g. eROSITA, Athena) it is important to understand the origin and composition of spectra observed for these systems. We aim to shed more light on the spectral composition of galactic X-ray emission by post-processing output from the hydrodynamic Magneticum Pathfinder simulations with our virtual X-ray simulator PHOX. In addition to producing synthetic X-ray spectra for accreting super-massive black holes and the hot gaseous component in the simulations we implement an empirical approach accounting for the X-ray emission of the stellar component, while allowing for known scaling relations to emerge self-consistently. Having access to these sources of X-rays independent of each other will improve our understanding of galactic X-ray spectra obtained from real observations.

Stephan Vladutescu-Zopp

Impact of the Hydro-Scheme on Simulations of Galaxies/Galaxy clusters

There exist a variety of different hydrodynamical codes with different approaches how to discretize space and solve the hydrodynamical equations. Examples are smoothed particle hydrodynamics (SPH), adaptive mesh refinement for a stationary mesh or moving mesh codes. All of which have different advantages, but also disadvantages. Meshless Finite Mass (MFM) is an alternative approach combining a moving-mesh with SPH.

In this thesis, we implement MFM into OpenGadget, as an alternative to SPH. We test it's capabilities as well as limitations in different idealised test-cases. Finally, we aim to compare, how it affects the evolution of galaxies / galaxy clusters.

Frederick Groth

Cosmic Rays in cosmological MHD simulations

We aim to study the impact of Cosmic Rays (CRs) in cosmological simulations of structure formation. To do this we employ and extend the spectral CR model we implemented in OpenGadget3. This allows us to follow an additional fluid component and analyze it’s assumed role in e.g. feedback mechanisms, magnetic field amplification and star formation. The spectral scheme makes it possible to not only study the kinetic impact, but also self-consistently model observables such as synchrotron emission by relativistic electrons.

Ludwig Böss

Dynamics of the interstellar medium

Filamentary structures in the interstellar medium play a vital role for stellar formation. Former theoretical investigations mainly focused on properties of cylindrical shaped filaments. However, observations of filaments show much more complex structures such as fork-like split-ups. This morphology may indicate filaments which are in the process of merging. We investigate under which conditions such mergers happen, how these evolve, what the resulting properties are and whether we can observe them. In order to address these questions we perform hydrodynamic simulations with the adaptive mesh refinement code RAMSES. We compare the results from simulations with analytic approaches in order to understand and describe the underlying mechanisms of the merger.

Elena Hoemann

A dress code for galaxies: how the interplay of gas, stars, dark matter and environment shapes their appearance in simulations

The formation and evolution of galaxies is still not fully understood. Especially the details of how the different types of galaxies have formed has been a matter of debate for many decades. Observations only show snap-shots of galaxies and one has to put together many pieces of this complex puzzle. In this work, we analyze galaxies extracted from the state-of-the-art hydrodynamical cosmological simulations taken from the Magneticum Pathfinder simulation set, in which galaxies form that reproduce many observational scaling relations.

Each chapter of this thesis addresses a different aspect of the interplay of the halo and the galaxy residing within it. For this, various estimators and indicators of galaxy formation channels, such as the kinematics of the galaxy components, the satellites and the environment, as well as the stellar populations, are discussed. We show that the morphology of a galaxy is closely related to the details of its evolutionary history, in particular to the distribution of the angular momentum and the stellar population. Furthermore, we show the influence of the environment, in which a galaxy forms, on its angular momentum, its kinematics and its morphology. From this we can conclude that the interaction of mass and angular momentum is an important tracer of the morphology and other kinematic and intrinsic properties of the galaxy.

Adelheid Teklu

Adelheid Teklu: Thesis

A web portal for hydrodynamical, cosmological simulations

The current generation of hydrodynamic cosmological simulations is facing a number of challenges when it comes to running and analysing larger and more resolved volumes in order to compare numerical studies with observational data. First, simulation codes need to fully exploit the computational capabilities of current and future generations of

supercomputers. Additionally, the amount of data generated by the most recent hydrodynamic simulations (>0.5 PB) poses a physical barrier when it comes to opening the access and sharing results with the scientific community: queries, lookups and filtering over such high amount of data need that are often not part of the background knowledge of a scientist working in such field; additionally, since only a HPC storage is capable of containing such amount of data, this prevents a public access of the scientific results, as scientists are required to apply and register to HPC facilities.

There I work on all challenges described above:

(i) a tailored optimisation and a refactor of a widely used code for simulations (Gadget3) made it possible to scale over the full SuperMUC to run the largest, cosmological simulations with baryon physics of the time (Magneticum Box0/mr and Magneticum Box2b/hr, PI Dr. Klaus Dolag),

(ii) a web portal to share such high amount of data by means (c2papcosmosim.uc.lrz.de),

(iii) a detailed study and comparison with observations of the simulated galaxy clusters over unprecedented simulated range of mass for hydrodynamic simulations and

(iv) to port the code to the GPUs in order to exploit the future generation of supercomputers. In order to relieve Gadget3 from its bottlenecks and scale it over the whole SuperMUC, it was not only necessary to have a deep knowledge of HPC,

communication protocols and parallelisation schemes: a complete change in the underlying neighbour search of Gadget3, which exploits space-filling curve ordering of particles, made it possible to let the code spend most of computing time in actual physical computation.

Antonio Ragagnin

Antonio Ragagnin: Thesis

Modelling active galactic nuclei in cosmological simulations: how sub-grid models help to reveal the driving mechanisms of nuclear activity

Although it is generally accepted that Active Galactic Nuclei (AGN) are driven by supermassive black holes (SMBHs) which reside in the centres of galaxies, their detailed physical driving mechanisms are not yet fully understood. In this thesis we make use of the Magneticum Pathfinder simulation set, which is a set of cosmological hydrodynamic simulations with different resolutions and volumes. In these simulations sub-grid models are used to mimic the growth of BHs as self-consistently as possible, assuming that the accretion rate onto the BH and the associated AGN feedback depend on the properties of the surrounding gas.

Cosmological simulations, which reproduce observed properties of BHs and their host galaxies, are not only an ideal testbed to study the formation and evolution of galaxies, but also to get insights into the driving mechanisms of AGN activity. The Magneticum Pathfinder simulations follow the dynamical evolution of BHs during galaxy mergers down to the resolution limit and, thus, they enable to investigate in detail the role of mergers for driving nuclear activity. Thereby, they do even produce a number of SMBH pairs with separations of only a few kpc, including dual AGN. Since the probability for AGN activity in our simulations increases with decreasing separation between the SMBHs, one might expect that galaxy mergers play a major role for driving AGN activity. However, turning towards the overall AGN population, we find that only a small fraction of AGN is driven by recent galaxy mergers. Finally, we use a large sample of simulated AGN to relate AGN to their host dark matter haloes. This reveals their large scale distribution, which turns out to be far more complex than that of the overall simulated galaxy sample.

Lisa Steinborn

Lisa Steinborn: Thesis

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

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

Alessandro Ballone

Alessandro Ballone: Thesis

The Outer Structure of Elliptical Galaxies and their Dark Matter Halos

The outer haloes of elliptical galaxies have been studied by observations of planetary nebulae as tracers for the LOSVD for several years to adress the questions of the nature of the Dark Matter halo they are embedded in and the mechanisms that drive the formation of elliptical galaxies, revealing a huge variety of different profiles, some flattening to nearly constant values, some increasing again in the outer part and some decreasing fastly, showing nearly no evidence of a dark matter halo. We try to explain the nature of the different profiles by studying different evolution scenarios for elliptical galaxies from simulations.

Rhea-Silvia Remus

Rhea-Silvia Remus: Thesis

Impact of massive stars on the surrounding medium

The aim of this project is to shed light on the impact of massive stars on the interstellar medium (ISM) in their surroundings. A good example of a region revealing such interactions between stars and the ISM is the Orion/Eridanus Superbubble (OES), a cavity blown by stellar winds and supernova explosions. This region has the advantage of being well observed. Its interaction with the local bubble, the dilute region in the ISM in which our sun is located, makes this zone even more interesting. We have developed a population synthesis code using modern stellar models to calculate the output of mass and energy from groups of massive stars, so-called OB associations. The spread of the ejecta into the ISM is followed with hydrodynamical simulations. The observational constraints on the 26Al distribution provide information on the time scales of the interaction process, since 26Al is a radioactive trace element that decays approximately a million years after being ejected from the stars. Thus, the spread of 26Al in different hydro models will help to understand the peculiar shape (distribution of density, shocks, evolution of star birth regions) of the OES.

Katharina Fierlinger

Katharina Fierlinger: Thesis

Massive star feedback and triggered star formation

Over their lifetime massive stars strongly affect the surrounding cloud. Strong stellar winds and ionizing radiation create HII regions, generate bubbles and pillar-like structures. The compression of material by the wind and the radiation shocks eventually leads to gravitational collapse and subsequent star formation. To study the effects of massive star feedback on the surrounding cloud, we perform numerical simulations using smooth particle hydrodynamics (SPH) and perform a detailed comparison of the results with multi-wavelength observations of the Carina nebula which is the most nearby southern region with an important population of massive stars.

The objectives are:

to determine the relative importance of ionizing feedback and stellar winds from high mass stars.

to understand the effects of massive star feedback on the star formation process, i.e. to determine whether star formation is inhibited or rather triggered by stellar feedback.

to assess the importance of the second generation of stars in comparison to the first one in a star forming region.

Image: A pillar of gas in the Carina Nebula. Radiation and fast winds from the stars sculpt the pillar and cause new star formation within it (Credit: NASA, ESA, and the Hubble SM4 ERO Team).

Judith Ngoumou

Judith Ngoumou: Thesis

Simulating Star formation near the Galactic Centre Black Hole

In this work we try to understand the formation of the discs of stars near the Galactic Centre in our Milky Way, as observed by the infrared group at the MPE (Genzel et al. 2003, Paumard et al. 2006, Bartko et al. 2009). For this we simulate the infall of molecular clouds onto the central black hole using the smoothed particle hydrodynamics (SPH) code GADGET2. During the encounter the clouds engulf the black hole in part, leading to gas streaming around the black hole with opposite angular momentum. This gas collides and settles into an eccentric accretion disc around the black hole which eventually becomes unstable and fragments into the observed stellar disc.

Christian Alig

Christian Alig: Thesis

Deriving a clump mass function of the Carina Nebula

The Young Stars & Star Formation group (Head: Prof. Thomas Peibisch) is currently involved in a large multi-wavelength project to study the young stellar populations in the Carina Nebula. This site of very recent and ongoing massive star formation allows a detailed look at the interaction of the winds and radiation of the numerous very massive young stars with the surrounding molecular clouds. With near-infrared, X-ray, and sub-mm observations we will investigate how the feedback from the massive stars disperses remnant clouds at some locations and triggers new generations of stars in other locations. I am using sub-mm data which trace the cold dust to derive a clump mass function of the Carina Nebula. Our aims are to investigate the cloud morphology and the effects of massive stellar feedback on the molecular cloud.

Stephanie Pekruhl

Stephanie Pekruhl: Thesis

Studying the physics of galaxy clusters by simulations and X-ray observations

Clusters of galaxies are optimal targets to study the large--scale structure of the Universe as well as the complex physical processes on the smaller scales. It is therefore vital to unveil cluster intrinsic structure, precisely estimate their total gravitating mass, and accurately calibrate scaling relations between observable quantities. A promising approach to achieve a more detailed picture of such complicated objects is found in the comparison between hydrodynamical numerical simulations of galaxy clusters and X--ray observations.

Veronica Biffil

Veronica Biffil: Thesis

Supernova-driven Galactic Winds

Galactic winds are common features within Lyman-alpha emitting galaxies at redshifts z>2. It however remains unclear what mechanisms are responsible to launch this type of outflow. The underlying project is based on hydrodynamic grid simulations with NIRVANA to investigate the conditions for a supernovae-driven galactic wind, and will also include a detailed parameter studies.

Wolfgang von Glasow

Wolfgang von Glasow: Thesis

Studying the survival of galaxies in hydrodynamical simulations of clusters

The project aims at investigating galaxy cluster formation and evolution by means of numerical simulations performed with a modified version of the TreeSPH code GADGET-3. This new version of the code employs adaptive softening to describe the gravitational interaction between the simulation particles; having this quantity variable in space and time, as opposed to having it fixed at the beginning of the simulation, allows to increase the spatial resolution in overdense regions whilst keeping particle-particle noise under control in less dense environments. Simulations involving gravitational as well as gas dynamics are likely to considerably benefit from the adoption of this scheme: the adaptive behaviour of the resolution scale should allow to follow the collapse of dark matter and particularly gas down to scales which are currently unachievable in standard simulations at comparable mass resolution, thus providing a more reliable representation of the behaviour of galaxy-like substructures.

Francesca Iannuzzi

Francesca Iannuzzi: Thesis

Formation of cold filaments and interstellar turbulence

I study the formation of cold filaments in the ISM with hydrodynamical simulations of wind-blown superbubbles from OB associations using the RAMSES code. I am also interested in the drivers and properties of interstellar turbulence. The picture shows a zoom-in on one of the formed filaments in the simulation. Axes are in parsecs, shown is logarithm of hydrogen number density.

Eva Ntormousi

Eva Ntormousi: Thesis

On the non-thermal emission in galaxy clusters

We investigate the transient phenomenon of radio haloes - Mpc sized, diffuse radio sources found exclusively in a fraction of merging galaxy clusters. The non-thermal spectrum suggests that in the intra cluster medium Cosmic Ray electrons interact with magnetic fields to emit Synchrotron radiation. Using the cosmological MHD SPH code Gadget3 we investigate Secondary and, for the first time, Reacceleration models as sources for the short lived cosmic ray electrons.

Julius Donnert

Julius Donnert: Thesis

Origin of the anti-hierarchical growth of black holes in the universe

In our current picture of galaxy formation, it is commonly accepted that every spheroidal galaxy hosts a supermassive black hole (SMBH) in its center. Moreover, SMBHs are found to be tightly correlated to properties of their host galaxies, as luminosity, bulge mass, velocity dispersion. This suggests a co-evolution of galaxies and black holes. However, detailed physical processes are still not well understood. One puzzling question, which we assess in this study, is to understand the observed downsizing trend in black hole growth. Investigating the number density evolution of AGN, observations show that luminous AGN peak at higher redshifts than less luminous ones (see colored dashed lines and grey shaded areas in the left image), implying that massive black holes form already very early in the universe, whereas less massive objects predominantly seem to form at later times. However, in order to explain the observed downsizing within a hierarchical structure formation model, accretion mechanisms onto the black holes and their corresponding efficiences will be of crucial importance. Thus in order to investigate this problem, we use a semi-analytic model, where we find additional modifications to be important ingredients in order to match the observations. This is illustrated by the solid, colored lines in the panel on the left-hand side showing a reasonably good agreement with the observations.

Michaela Hirschmann

Michaela Hirschmann: Thesis

Magnetic field evolution in spiral galaxies

Magnetic fields are believed to be importanant in many astrophysical processes like star formation, cosmic ray confinement and jet formation. However, despite their importance, the origin and evolution of magnetic fields in galaxies is still not well understood. Magnetic field evolution is tightly coupled to galactic evolution. In the standard cold dark matter clustering models, galaxies evolve through several major and minor mergers of galaxies and galactic subunits. Thus, galactic interactions should be a crucial part of magnetic field evolution, which is why we investigate interacting galaxies including magnetic fields using N-body/SPH simulations. Our studies show that magnetic fields are efficiently amplified up to equipartition between magnetic and turbulent pressure during galactic collisions. Moreover, magnetic fields seem to be important for the propagation of shocks in the interstellar medium. Therby, the Mach numbers of the shocks are higher for stronger magnetic fields, suggesting that the shocks are supprted by magnetic pressure. Artificial radio maps of our simulated systems are in good agreement with observations.

Hanna Kotarba

Hanna Kotarba: Thesis

Hydrodynamical Instabilities and the Trace of Dark Energy within the CMB

Part I: The first part concentrates on the numerical description of the Kelvin-Helmholtz instability (KHI), based on the two most widely used approaches, 'Smooth particle Hydrodynamics' (SPH) and grid based codes. Re-derving the analytical linear viscous KHI growth rate we study the evolution in detail and compare the simulated amplitudes with the analytical expectation.

Part II: The second part analyzes the influence of Dark Energy on cosmic structures, which results in non-Gaussian contributions known as secondary anisotropies. In particular, the Rees-Sciama effect (which includes the nonlinear evolution of structures) plays a crucial role. The effect of different DE models, such as quintessence can be studied analytically with the three point correlation function, or the bispectrum.

Veronika Junk

Veronika Junk: Thesis

Axion Quark Nuggets – Testing a Novel Dark Matter Model using the Cosmological Simulation ‘SLOW’ and Inferring its Observational Detectability

Here, we analyze a novel, promising Dark Matter candidate called Axion Quark Nuggets (AQNs) in the context of traceable electromagnetic signatures in galaxy clusters after interactions with baryonic matter. We use a cosmological simulation called "Simulation of the LOcal Web (SLOW)", which simulates the local universe and therefore contains galaxy clusters that resemble digital twins of their real counterparts. We propose that the Fornax and Virgo clusters are the most promising candidates hosting detectable AQN signatures.

Julian Sommer

Julian Sommer: Thesis

Spatially-Resolved Age and Metallicity of Galaxies and Their Stellar Shells and Streams in the Magneticum Simulation

IFU surveys and stellar population synthesis made it possible to investigate not only the global ages and metallicities of galaxies, but also their spatial distribution, which play a major role as tracers of galaxy formation history. Utilizing the hydrodynamic cosmological simulation Magneticum Pathfinder, I examined these properties in galaxies and their stellar tidal shells and streams. In the simulation, global metallicity and age scaling relations are consistent with observations. According to the radial age profiles, spheroids are old everywhere, whereas disks become younger outside the central region. I found that metallicity gradients in general are negative and suggest an “inside-out” progression of star formation. Additionally, I identified galaxies exhibiting a young positive and old negative metallicity gradient. This can be explained by a formation scenario of quenching and subsequent restarting of star formation. In the outskirts of galaxies, I analyzed stellar shells and streams and their progenitors. The velocity dispersion in both types of features is lower than in their surroundings, while their ages do not significantly differ in this aspect. However, shells are more metal-rich, while streams are metal-poor compared to their environment. This is likely related to the mass-metallicity relation because stream progenitors are less massive than shell progenitors, and therefore also less metal-rich. With these new insights from a cosmological simulation, the formation history of observed galaxies, shells, and streams can be further constrained.

Johannes Stoiber

Johannes Stoiber: Thesis

Collecting Shells in the Tides: Formation of Dwarf Galaxies From Mergers Inside Galaxy Clusters

Although galaxy interactions are thought to provide a possible cradle for low-mass objects, environmental influence could still be a crucial driver for their formation and evolution. This hypothesis is stimulated by observations of star forming knots inside extended tidal tails of ongoing galaxy mergers in clusters. Such an arrangement prompts the intriguing question as to whether cluster environments could support tidal dwarf formation. I test this evolutionary channel by performing hydrodynamical simulations of galaxy mergers inside clusters. I demonstrate that environments indeed are capable of stripping tidal dwarf galaxies. Exposed to ram pressure, these gas dominated objects exhibit high star formation rates, while also loosing gas at the high-mass end. With time, they either evaporate due to their low initial mass, or are disrupted as soon as they reach the cluster center. Intact dwarf galaxies can still be found ~4 Gyr after the merger event, demonstrating that such objects can prevail for a significant portion of the Hubble time. The obtained results indicate that the fraction of dwarf galaxies with tidal origin could be significantly higher than in current estimates adopted in the literature, since the latter do not consider environmentally supported formation scenarios.

Anna Ivleva

Anna Ivleva: Thesis

A Subgrid Model for Supernova Remnants as Sources of Cosmic Rays in Cosmological Hydrodynamical Simulations

The vast majority of Galactic cosmic rays are accelerated at the strong shock waves of supernova remnants, which should therefore be implemented as subgrid sources in any large-scale simulation code that contains a model for spectral cosmic rays. The common approach is to describe the complicated spectra of high-energy protons end electrons released by a supernova remnant over its lifetime by a simple power-law in momentum space. In this Master's thesis we propose a more realistic treatment of supernova remnants as cosmic ray sources, which is based on recently published models that include descriptions for the time evolution of shock radius and velocity, particle escape from the remnant, amplification of the self-generated magnetic field, and energy losses from adiabatic expansion as well as from synchrotron radiation and inverse Compton scattering.

Daniel Karner

Daniel Karner: Thesis

Spin Evolution of Galaxies in the Magneticum Pathfinder Simulations

The galaxies we observe today display a large variety of apparent shapes from near-perfect disks like the void galaxy MGC+01-02-015 to massive elliptical BCGs. These morphological differences emerge from different formation histories of galaxies. Their stellar angular momentum vectors (spin) change in magnitude and orientation (flips) through the interaction with the cosmic web via tidal torque, smooth accretion and merger events.

By using the highest-resolution box of the Magneticum Pathfinder simulations, I trace the resolved stellar angular momentum of galaxies through time. I explore the relation between spin flips and evolution of a galaxy's kinematic morphology (determined by its b-value) as well as the connection to star formation.

I further show how well spin flips can be predicted from merger accretion and finally link the spin change histories to the state of galaxies at z = 0.

Silvio Fortuné

Silvio Fortuné: Thesis

Are You Bound or Just Projected? The Behavior of Substructures from Expansion to Galaxy Clusters

In our Universe, two dark components play an intricate role in forming the structures that we can observe today. On the one hand, dark matter still presents an unresolved puzzle. One imprint of dark matter that can be used to understand its nature, is left in the distribution of mass in the substructures in galaxy clusters. Here, observations have reported mass fractions that are difficult to reproduce in simulations, challenging our current paradigm. Using the cosmological hydrodynamical simulation Magneticum Pathfinder, I showed that this discrepancy results from projection effects in measurements, explicitly at the case of the famous cluster Abell2744. More illusive, on the other hand, is the dark energy component, for which the influence on the internal structure properties is still not well understood. Here, this thesis targets the question in how far the orbits of particles are influenced by the dark energy, and which effects this can have over cosmic time.

This thesis was awarded with the LMU Research Prize 2022.

Lucas Kimmig

Lucas Kimmig: Thesis

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.

Bendix Hagedorn

Bendix Hagedorn: Thesis

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.

Tirso Marin

Tirso Marin: Thesis

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.

Stefan Lüders

Stefan Lüders: Thesis

Protoclusters of Galaxies in Cosmological Zoom Simulations

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.

Elena Hernández Martínez

Elena Hernández Martínez: Thesis

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.

Lucas Valenzuela

Lucas Valenzuela: Thesis

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

Ludwig Böss: Thesis

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

Maximilian Kühn: Thesis

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.

Pascal Förster

Pascal Förster: Thesis

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

Eirini Batziou: Thesis

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

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

Geray Karademir: Thesis

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.

Christoph Becker

Christoph Becker: Thesis

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

Marcel Lotz: Thesis

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.

Lennart Reb

Lennart Reb: Thesis

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

Emilio Mevius: Thesis

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.

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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.

Felix Schulze

Felix Schulze: Thesis

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.

Jens Stücker

Jens Stücker: Thesis

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

Adelheid Teklu: Thesis

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

Lisa Bachmann: Thesis

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

David Schlachtenberger: Thesis

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

Georg Michna: Thesis

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

Max Brunner: Thesis

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.

Johannes Stoiber

Johannes Stoiber: Thesis

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.

Sebastian Langer

Sebastian Langer: Thesis

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.

Franziska Eisner

Franziska Eisner: Thesis - Zulassungsarbeit Lehramtsstudium

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.

Alexander Mayer

Alexander Mayer: Thesis

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.

Stefan Lueders

Stefan Lueders: Thesis

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.

Ludwig Boess

Ludwig Boess: Thesis

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.

Jennifer Hinz

Jennifer Hinz: Thesis

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.

Maximilian Kuehn

Maximilian Kuehn: Thesis

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.

Andreas Hofmann

Andreas Hofmann: Thesis

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.

Pascal Förster

Pascal Förster: Thesis

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.

Michael Hartmann

Michael Hartmann: Thesis

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.

Miriam Keppler

Miriam Keppler: Thesis

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.

Norbert Konrad

Norbert Konrad: Thesis

Spiral galaxies in cosmological simulations

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.

Felix Schulze

Felix Schulze: Thesis

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.

Torben Erik Simm

Torben Erik Simm: Thesis

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.

Lucas Sommer

Lucas Sommer: Thesis

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.

Adelheid Teklu

Adelheid Teklu: Thesis

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.

Christian Franik

Christian Franik: Thesis

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.

Sheila Hieber

Sheila Hieber: Thesis

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.

Klaus Jakabos

Klaus Jakabos: Thesis

Filamentary structure of wind blown superbubbles

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.

Birgitta Müller

Birgitta Müller: Thesis

The influence of central supermassive black holes on major merger remnants

David Schlachtenberger

David Schlachtenberger: Thesis