Analysis of theoretically modelled galaxy clusters

• Autores: Ana Contreras de Santos
• Directores de la Tesis: Alexander Knebe (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2024
• Idioma: español
• Número de páginas: 131
• Títulos paralelos:
  • Análisis de cúmulos de galaxias modelados teóricamente
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • Galaxy clusters are the largest known gravitationally bound structures in the Universe, with masses up to a few 1015 solar masses. In the hierarchical model of structure formation, they lie at the top of the hierarchy. They have grown and evolved through the collapse of initially overdense regions and the subsequent accretion of material and merging processes with other systems. Consequently, the study of galaxy clusters provides valuable insights into the processes of large-scale structure formation in the Universe, making them indispensable cosmological probes. They also offer a great environment to investigate galaxy formation and evolution, as driven by different astrophysical processes taking place inside them. From a theoretical perspective, due to the high complexity underlying their evolution, the best way to model them is through numerical simulations. Hydrodynamical simulations, in particular, follow the behaviour of the dark matter, stars and gas by numerically solving the corresponding equations. This approach allows for a detailed study of how galaxy clusters and their contents evolve naturally within the broader context of the cosmic web.

    In this thesis, we make use of a set of cosmological simulations from THE THREE HUNDRED project. This data set consists of a suite of 324 hydrodynamical resimulations of cluster-sized halos and the regions of radius 15 h−1Mpc around them. These regions, taken from a parent dark matter only simulation, have been resimulated with different hydrodynamical codes and subgrid physics implementations, enabling the identification and analysis of the diverse structures.

    Across the different chapters of the thesis, we use these simulations to study distinct aspects of galaxy clusters. We start by analysing galaxy cluster mergers within their mass accretion history, identifying mergers as significant mass increases that happen over a short period of time. We measure the dynamical state of the clusters around the time of mergers using theoretical indicators and, based on this, we define a merger phase, during which the cluster is affected by the merger. We then investigate the brightest cluster galaxies of merging clusters. By comparing the properties before and after the merger, we show how they grow mainly through accretion of stars, with a small contribution from a merger-induced burst in star formation, that affects the luminosity and colour of the central galaxies.

    The second approach taken in the thesis involves the galaxy population within these simulated regions and, in particular, pairs of galaxies that lie close to each other. We focus both on checking if observed pairs are physically close and if they are gravitationally bound. For the first purpose, we show that selecting the galaxy pairs based on the stellar mass, metallicity, colour, shape and stellar-to-halo mass ratio of the involved galaxies can improve the likelihood of the observed pairs being close in physical distance. For the latter purpose, we demonstrate how a machine learning algorithm can be trained to identify gravitationally bound pairs based only on observable properties of the galaxies.

    The last part of the thesis explores the intra-cluster light of THE THREE HUNDRED clusters, a diffuse component from stars in the cluster that do not belong to any individual galaxy. Given the improved resources from low surface brightness observations and from simulations, this is a topic of timely relevance in the field of galaxy clusters. In our work, we show that, although there is significant scatter across the cluster sample, this component is non-negligible for all clusters and contains information about the evolutionary history of the cluster. We also investigate the relation between the intra-cluster light and the dark matter component of clusters, by computing and comparing their density and velocity dispersion profiles. This way we contribute to determine how observations of the diffuse component can unveil information about the underlying total mass distribution.

    Along this thesis, we have developed new methods to identify, in the simulations, the different components under study: cluster mergers, the brightest cluster galaxy, the intra-cluster light and the pairs of satellite galaxies. As well as obtaining a deeper understanding of the physical processes that dominate them, we characterised their properties and utilised their observable features to provide new valuable tools to analyse observations.

    Our work has inspired further studies which are described in the last Chapter. We also illustrate there how the three parts of the work are interconnected and affecting one another, thus highlighting the importance of taking different approaches for the study of galaxy clusters.