Computational Modeling of the Baryon Content of Galaxies and Clusters in Cosmological Simulations

Abstract

Cosmological simulations aim to self-consistently model the physics that shapes the distribution of baryons in our Universe. Galaxy mergers and feedback from supermassive black holes are some of the most violent physical processes in astrophysics, and they leave a major imprint on the interstellar and intracluster medium. In the first part of this thesis, I will explore the formation mechanism of stellar shells in cosmological simulations. Shells are low surface brightness tidal debris that form interleaved arcs of overdense caustics on both sides of the galaxy center. We identify shells using stellar surface density maps, and we develop stellar history catalogs to trace the birth, trajectory, and progenitors of each individual star particle contributing to the tidal features. Using supervised classification models, we identify the most important features that distinguish shell-forming collisions. Our study indicates that, due to dynamical friction, more massive satellites are allowed to probe a wider range of impact parameters at accretion time, while small companions need almost perfectly radial infall trajectories in order to produce shells. In the second half of the thesis, we focus on how the observable thermodynamical properties of the intracluster medium reflect the complex interplay between AGN feedback and the gravitational collapse of halos. Using the IllustrisTNG simulations, we measure the X-ray emission and the impact of gas on CMB through the Sunyaev-Zel'dovich effect. We produce mock X-ray observations of simulated halos using methods that are consistent with observational techniques, and we account for the bias and scatter introduced by estimated halo masses. Furthermore, we introduce a new model for a smoothly broken power law, which offers insights into the break in scaling relations as a function of halo mass. Our results highlight the influence of AGN feedback on X-ray and SZ measurements over a wide range of mass scales: from galaxies and groups to the most massive clusters of galaxies.