From galaxy clusters to cosmology

Hernandez Lang, Daniel (2025): From galaxy clusters to cosmology. Dissertation, LMU München: Fakultät für Physik

Abstract

Galaxy clusters are the largest collapsed structures in the universe. Using the halo mass function (HMF), we can predict the number of clusters within a mass range for a fixed redshift. The HMF, however, depends on cosmological parameters such as the total matter density, Ωₘ, and the amplitude of matter density fluctuations, σ₈. Consequently, the observed number of galaxy clusters can provide constraints on these parameters. Since cluster masses are not directly observable, scaling relations that link observable properties to true cluster masses are crucial. In this context, understanding the creation of galaxy cluster catalogs—including selection and confirmation processes—and accurately constraining the parameters of the observable-mass relation are fundamental for the use of cluster number counts as cosmological probes. My first study focuses on the analysis of the merging galaxy cluster SPT-CL J0307-6225. Through an analysis of its merging dynamics, I separate the substructures and find a likely mass ratio of ~1.3. On the other hand, the analysis of the galaxy population hints towards a previous merger in one of the substructures. In my second study, I use galaxy cluster candidates, selected using the thermal Sunyaev-Zeldovich effect with data from the Planck (down to S/N= 3), and look for optical counterparts using photometric data from the Dark Energy Survey data release 3. The final catalog, PSZ-MCMF, contains over 800 confirmed clusters with a purity of 90\%. In the third study I demonstrate how to use a X-ray selected and optically confirmed galaxy cluster sample (RASS-MCMF) to get cosmology constrains. Using a mock cluster sample with properties similar to the 99\% pure subset of RASS-MCMF (~5000 clusters), I forecast constraining powers of 0.026, 0.033, and 0.15 (1σ) for the parameters Ωₘ, σ₈, and w respectively. Finally, in my fourth study, I expand the analysis from the third study by improving the modeling of the RASS-MCMF sample. These improvements include a new method for the abundance likelihood and the explicit inclusion of weak-lensing mass calibration. The results indicate that these improvements yield constraining power comparable to the latest results from SPT and eRASS1.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: galaxy clusters, cosmology
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 530 Physik
• Fakultäten: Fakultät für Physik
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 4. Februar 2025
• 1. Bericht­erstatter:in: Mohr, Joseph