Dottorato in ASTRONOMIA

Titolo della tesi: The search for Cosmic Web and detailed study of galaxy clusters with the Sunyaev-Zel’dovich effect

The Cosmic Web is the large-scale spatial arrangement of matter in the Universe, resulting from the hierarchical structure formation process. Galaxy clusters, the largest gravitationally bound systems in the Universe, are situated at the nodes of this Web and undergo continuous evolution through interactions and mergers. The goal of this PhD project is to investigate galaxy clusters and their connection to the Cosmic Web by using observations of the thermal component of the Sunyaev-Zel’dovich (tSZ) effect from the Planck satellite and the Atacama Cosmology Telescope (ACT). The tSZ effect is well-suited for revealing the diffuse baryonic component both within and outside galaxy clusters, and it is a valuable tool for studying large-scale structures. This study, in particular, focuses on the search for the warm-hot intercluster medium (WHIM), which could potentially account for a fraction of the missing baryons in the cosmic census. Observations of the tSZ effect, especially in pairs of merging galaxy clusters, are suggested as a means to reveal and study the WHIM. The first part of this research is dedicated to analysing galaxy cluster pairs to unveil bridges of diffuse matter possibly related to WHIM, using new high-resolution observations from ACT. The second part involves detailed studies of galaxy clusters and introduces a novel method for evaluating the morphology of their 2D images. This method involves analytical modelling through Zernike polynomials, a set of orthogonal functions widely used in adaptive optics. Through this innovative approach, the aim is to accurately infer the morphology of cluster images and derive a dynamical-state assessment for these systems. The new method is tested and validated on simulated data before being applied to tSZ observations of galaxy clusters from the Planck satellite.