Modelling of the relativistic Sunyaev-Zeldovich effect and related Compton scattering processes

Abstract

The Sunyaev-Zeldovich (SZ) effect is caused by Compton scattering where the electron population has far higher energies than the incident photons -- i.e., in the Doppler-dominated regime. As such, the SZ effect is a unique probe of galaxy clusters and groups, some of the largest structures in our Universe, where the electron populations lead to a distinctive signal in the scattering of the cosmic microwave background (CMB). This thesis contains an exploration of corrections to the SZ effect, alongside a discussion of analytic approaches to Compton scattering. In particular, in Chapter 2, using the Bahamas and Macsis simulations, I examine the appropriate temperature measures to derive the cluster-averaged relativistic SZ effect. This allows a comparison with other commonly used temperature measures, and the generation of temperature-mass scaling relations to allow for forward modelling of future cluster SZ observations. Chapter 3 extends this work to also compare to the IllustrisTNG, Magneticum and The Three Hundred Project simulations. We find consistency in the SZ temperature despite the wide range of simulation parameters and investigate the impact of these simulation parameters, such as feedback prescriptions and resolution. The agreement between simulations indicates an exciting avenue for observational and theoretical exploration, determining the extent of relativistic SZ corrections. In Chapter 4, a detailed examination of the radio SZ effect is carried out. This signal would be caused by a cosmological radio background scattering alongside the CMB in clusters. This chapter focuses on detailed modelling of kinematic and relativistic corrections to this signal, and the impact of anisotropies and variation in the radio background on the observed radio SZ signal. Chapter 5 examines the effects high-energy non-thermal electron distributions alongside anisotropic electron or photon distributions. Here an analytic form of the anisotropic scattering kernels for photons or electrons has been derived and investigated. An exploration of various toy-models of non-thermal distributions is carried out. Finally, in Chapter 6, a numerically stable form of the isotropic general Compton scattering kernel is presented and explored. Further extensions to analytic kernels for the low-multipole anisotropic Compton scattering problem are also derived and discussed. These allow for the rapid and accurate computation of scattering processes throughout the history of of the Universe.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Scott Kay (Supervisor) & Jens Chluba (Supervisor)