Evolution of galactic disks and spheroids

Abstract

In this Thesis the structural properties of galaxies using quantitative 2-dimensional bulge to disk decompositions are analysed across a range of environments and red- shifts. The study of morphological properties of galaxies is undergoing a significant progress since large galaxy surveys such as the Sloan Digital Sky Survey are producing a vast amounts of data enabling properties such as galaxy structure to be analysed on a statistical level. The wide-field imaging available today makes the studies of the nearby and high redshift environments comparable on a similar physical scale and depth. The advances in the theoretical studies and understanding the physics behind processes that govern galaxy formation and evolution make studies such as this one important since they provide basic estimates of galaxy structure that can be used to constrain the current theoretical models. By comparing the structural properties of bright cluster galaxies between z ~ 0.5 and present we are able to confirm that galaxies have undergone a high degree of evolution although the exact processes that govern this evolution still remain unresolved. In order to account for the evolution of z ~ 0.5 cluster spirals into present-day SOs a significant number of spiral galaxies (factor of 3) must have had their disks faded to make them drop .out of our magnitude limited sample. However, the structural properties between the faded-disk spirals and present day SOs are not consistent. One possibility is that the progenitor galaxies might have been accreted recently from the field and that these have also been previously pre-processed. The study of the structural properties of field galaxies has resulted in a potential evidence that galaxies in the field environment have an additional structural component or structural property that cannot be accounted for by the current 2- dimensional decomposition methods. This study has found that disks contribute about 3 times as much light as bulges to the total luminosity density of the local universe. Tighter constraints in terms of bulge and disk mass densities would help to constrain the current theoretical predictions.