Analysing Observables in Structure Formation Theories

Abstract

This thesis presents an exploration of various aspects relating to the formation and evolution of structure in the Universe. It focuses on two main observables which provide information on two distinct epochs of the Universe: Part I analyses the Cosmic Microwave Background (CMB) which is used to test early Universe theories and validate current methods for cosmological parameters estimation; Part II analyses the distribution, history and content of local galaxies with a view to learn about type Ia supernovae progenitors, assembly of stellar mass in galaxies and galaxy evolution. In Part I, a search for signs of non-Gaussianity in theWilkinson Microwave Anisotropy Probe is conducted, using the two-point correlation function of peaks (hot and cold spots) in the temperature field. A clear deviation from Gaussianity is found in both data releases, which is associated with cold spots, the southern hemisphere, large-scales and the galactic plane. The results indicate that the presence of un-subtracted foregrounds in the data are a more likely explanation for this signal than a cosmological origin, but the latter cannot be excluded. Part I further explores the two-point correlation function of temperature peaks as an estimator to constrain fNL, a specific type of non-Gaussianity. Using sets of non-Gaussian simulated maps with the correct cosmology and resolution, this thesis explores how accurately one can hope to constrain fNL when data from the upcoming CMB experiment Planck is available. Part II presents a novel method developed to extract the star formation history of a galaxy from its spectrum: VErsatile SPectral Analysis (VESPA). VESPA dynamically adapts the number of parameters it recovers from each spectrum to each galaxy, only recovering as much information as the data warrant. This insures the recovered solutions are dominated by the signal, not the noise, and allows robust recovery of star formation and metallicity histories and up to two dust extinction values per galaxy. VESPA was applied to the fifth data release of the Sloan Digital Sky Survey (SDSS) to construct a catalogue of histories for nearly half a million galaxies. Part II also explores how this catalogue can provide important information about the formation of structure in the local Universe. Specifically, this thesis: shows evidence for the presence of a short-lived progenitor to SNIa and explores VESPA’s potential role in future Dark Energy SNIa experiments; explores how changes in the Initial Mass Function affect stellar mass estimates and its consequences; and by using estimates of the galaxy mass function as a function of redshift (calculated using both the spectral fossil record and instantaneous star formation rate methods) explores the possibility of putting constraints on the merger history of present-day galaxies.