|dc.description.abstract||I have conducted two separate observational tests of the current theoretical
paradigm for galaxy formation and evolution, hierarchical galaxy formation in a
Cold Dark Matter dominated universe. The first project is a spectroscopic study
of nineteen low surface brightness galaxies observed with the 9.2m Hobby-Eberly
Telescope. I determine redshifts to all the galaxies, and report both emission line
and absorption line index strengths, where appropriate. Correlations are found between
the gas-phase metallicity indicators and the stellar indices which are sensitive
to both metallicity and age. I interpret the star formation and chemical evolutionary
histories of these galaxies using a combination of simple stellar population models
and nebular emission models. The correlations observed between emission and absorption
measurements place strong constraints on possible star formation histories.
We find that low surface brightness galaxies are a diverse class, with properties as
broad as those exhibited by the full range of high surface brightness galaxies.
The second project is a study of the ages in early-type field galaxies, and a
comparison with the ages found for a sample of cluster galaxies. I present preliminary
results and interpretations based on new stellar population modelling methods.
The new model explicitly accounts for age, metallicity, and α–abundance ratios for
the stellar population, by making predictions for low resolution line indices. I measure
the ages, metallicities, and α–abundance as a function of radius, from the center
of each galaxy to beyond one effective radius. The gradients are consistent with
younger, more metal rich stellar populations in the centers of most of the galaxies,
but a constant α–abundance ratio within any one galaxy.
I have generated an all-sky catalog which measures the local density of
galaxies around every galaxy at cz<10,000 km s
. This facilitates the creation
of low redshift field galaxy samples for follow-up study, in particular to study the
effects of environment on galaxy evolution. I attempt to quantify the effects on
the catalog of the varying spectroscopic survey completeness across the sky, and
compare my local density measures with published field galaxy samples. The full
catalog (42,024 galaxies, with ∼ 50 parameters per galaxy) is included in the electronic
version of this dissertation.||