University of Sussex
Irodotou, Dimitrios.pdf (12.91 MB)

The characterisation and origin of the morphology of galaxies across multiple scales and epochs

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posted on 2023-06-10, 00:18 authored by Dimitrios Irodotou
In the widely accepted lambda cold dark matter (ACDM) framework, dark matter haloes acquire their initial angular momentum through tidal interactions and grow in mass and size through accretion and/or repeated mergers. Galaxies form in the centres of these haloes when the baryonic matter collapses and the subsequent formation of stars occurs. Galaxies are complex systems whose properties reveal their evolutionary history. Understanding how they acquire their properties and identifying the dynamical processes responsible is a fundamental question in modern astrophysics. In this thesis, I address these issues by studying the characterisation and origin of the morphology of galaxies across multiple scales and epochs. For that purpose, I combine observational data with various theoretical tools, as outlined below. Determining which galaxies develop dynamical instabilities, which components are involved and how stability is restored is still an open question. Even though gaseous discs significantly contribute to the global stability, most semi-analytic models (SAMs) only identify and address stellar disc instabilities. Therefore, in Chapter 2, I introduce the new instability formulation we developed which significantly improves the predictions of the L-Galaxies SAM. The updated recipe takes into account the gravitational contribution of gas in conjunction with the stellar component and more accurately follows the physical processes responsible for bulge growth. Hence, our model produces galactic properties which are in closer agreement with observations than previous work. There is a prominent connection between understanding the formation and evolution of galaxies and exploring how and when galactic components form. Therefore, a method that accurately identifies the constituent stellar populations and provides an additional way of exploring their properties is of great importance. Hence, in Chapter 3, I introduced the new method we developed to identify kinematically distinct components. We applied our method to the Eagle cosmological simulation and studied the imprint of secular and violent processes on galaxies. By creating Mollweide projections of the angular momentum map of each galaxy’s stellar particles we identified a number of features which indicate distinct galactic morphologies. Thus, we were able to both classify and decompose galaxies and reproduce the observed tight relations. Finally, in order to advance the field of structure formation and improve our theoretical tools, it is imperative to understand our models and the non-linear effects they introduce. For that reason, in Chapter 4, I investigate how AGN feedback alters stellar dynamics and affects bar formation. I re-simulated three Auriga galaxies using two different AGN feedback prescriptions in an effort to constrain their impact on the halo and galaxy properties. In addition, we use Imfit to perform bar/bulge/disc decompositions and quantify the effect of AGN on the relative growth of each component.


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  • Physics and Astronomy Theses

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  • doctoral

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  • eng


University of Sussex

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