The evolution of galaxy structures from a Bayesian perspective

Galaxies--Evolution;Markov processes;Bayesian statistical decision theory

Argyle, Joshua J. ; Jairo, Méndez-Abreu ; Jairo, Méndez-Abreu

University:University of St Andrews

Department:Physics & Astronomy (School of)

关键词: Galaxies--Evolution;    Markov processes;    Bayesian statistical decision theory;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/15647/JoshuaArgylePhDThesis.pdf?sequence=2&isAllowed=y

来源: DR-NTU

【 摘 要 】

Galaxy structures in the local Universe are the result of an evolution spanning billions of years.The diversity in morphologies observed is due to mechanisms that could either be from externalinteractions or internal processes. The hierarchical merging of two massive galaxies has long beenthought to give rise to pressure-supported spherical structures, including elliptical galaxies and classical bulges. On the other hand, isolated galaxies may evolve at a much slower pace with the accretion of gas forming flattened rotationally-supported discs. Secular evolution could also result in newly formed internal structures, such as bars or discy-bulges. The first step in understanding the complex pathways that formed these monolithic beasts, we need to robustly measure their structures.This thesis investigates how the structure of galaxies have evolved over the last seven Gyrs. Inthe first part I present a new Bayesian Markov Chain Monte Carlo (MCMC) two-dimensional (2D)photometric decompositions algorithm called PHI. The purpose of the algorithm is to decompose agalaxy’s light profile into the various components that make-up the structure. By implementing athree level method, PHI is able to obtain a full understanding of the parameter space overcomingmany of the major issues previous codes have struggled with.The second part of the thesis describes the generation of synthetic galaxy images which are usedto test the robustness of PHIand to also highlight the cosmological and instrumental effects that maybias the outcomes. We also present is a performance test for the Bayesian application to bulge-discdecompositions of galaxies using images from the Sloan Digital Sky Survey (SDSS), also included isthe parameter estimation and model comparison method using the Bayesian Information Criteria.In the third part of this thesis we show how the use of Hierarchical Bayesian Models (HBM)can be used to describe structural scaling relations in the local Universe. A constant piece-wiserepresentation fully captures the underlying nature of the sample. This leads to the analysis ofmany structural scaling relations, one being the positive trend between the effective radius of thebulge and the Sérsic index.Lastly, a study investigating the structural evolution of galaxies within the COSMOS field in theredshift range 0.5 < z < 1.25 is presented. The flexible nature of the HBM allows for a detaileddescription of the build-up of galaxy structures in the local Universe.