Thesis Projects

Currently ongoing PhD projects

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

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