Evolution of Galaxies - Star Formation Histories in Nearby Spheroids

Abstract

This thesis is about an investigation into the formation of spheroidal type galaxies. The investigation began with modelling studies of early-type galaxies and spiral bulges (SBs). From galaxy formation modelling studies led by experiments with a sample galaxy, some results were obtained; nonsolar abundance ratios in Elliptical galaxies (Es) achieved better fits between model and data than solar abundance ratios. For both early-type and late-type galaxies, best fits with non-solar abundance ratios were more constrained than in the solar abundance ratio case. A strong link between star formation histories and the supernova Ia rate for the early and late-type galaxies was shown. The model code itself was tested by way of pseudo galaxy experiments, and shown to reliably reproduce model parameters. In the topic area of galaxy formation, regions of spectra particularly sensitive to a galaxy's age and metallicity were measured as equivalent widths and then calibrated to the common scale of the Lick Indices. The Lick Indices were used in deriving all key results throughout the thesis.

The modelled sample of galaxies from Proctor & Sansom (2002) lacked data on low velocity dispersion (a) galaxies for line strengths versus kinematics correlations. In regards to low a galaxies, Low Luminosity Es (LLE5) were considered to be likely candidates. Long-slit spectra of a sample of 12 LLEs, taken at the European Southern Observatory New Technology Telescope, were sub-selected for their low velocity dispersions. The spectra of 10 of these LLEs were successfully reduced. Line strengths and kinematics were measured. The Lick Indices of these LLEs were correlated with velocity dispersion (a), alongside the previously modelled companion data set. Ages and metallicities of the LLEs were estimated. From these results, the LLEs were found to have significant correlations of line strength versus a with SBs. However, the LLEs do not appear to be younger than SBs, but younger than Es. The LLEs seem to consist of a low metallicity group (possibly misclassified dwarf spheroidal galaxies) and a high metallicity group. Future possible work that may uncover which models of galaxy formation for high and low metallicity LLEs these results support is suggested.