Ph.D. Thesis

A Phenomenological Study of
Star Formation and Chemical Evolution
in Nearby Galaxies

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Introduction plus contents, abstract, acknowledgements, etc.
Data including sample, UV photometry and optical spectroscopy
Migration of spirals
Virgo colour profiles and AGN feedback
The stellar mass - metallicity relation
Discussions and conclusions
Appendices, but tables are updated/improved in published papers.

Abstract

The processes influencing galaxy evolution in the local universe are investigated using a dataset of multiwavelength observations for a new sample of galaxies. The sample is volume and mass limited, and includes galaxies of all morphological types inhabiting a range of different environments, from galaxies in the dense core of the Virgo cluster to relatively isolated systems. As such, the sample is ideal for disentangling the internal and environmental processes driving evolution. The combination of ultraviolet, optical, near- and far-infrared imaging, nuclear and integrated optical spectroscopy, and atomic hydrogen emission line data, traces the key galaxy components, such as the stellar populations, gas content, star formation, metallicity and nuclear activity. The main aims of this thesis are: (a) an investigation into the evolutionary histories of nearby galaxies to determine the dominant mechanism quenching star formation; (b) the determination of the impact of feedback from active galactic nuclei on star formation; and (c) a study of the evolution of the chemical composition of star-forming galaxies in different environments. The analysis performed in this thesis confirms recent observations of a population of late-type galaxies with reduced levels of star formation. I demonstrate that feedback from active nuclei is unlikely to be the dominant mechanism quenching star formation and driving the evolution of these late-type galaxies. In fact, galaxies with quenched star formation are typically gas deficient systems residing in the cluster environment, suggesting that environmental effects are responsible for removing the gas required to fuel star formation in these objects. A fraction of quenched late-type galaxies are, however, not gas deficient, and form a more heterogeneous class of objects with probably more complex evolutionary histories. In contrast to the case of star formation, the chemical evolution of star-forming galaxies, as traced by the stellar mass-metallicity relation, is shown to be invariant across different environments, suggesting that chemical evolution may be driven by internal processes, thus placing an upper limit on the effect of the environment. The clear observational evidence presented here indicates that, in the concordance model of galaxy formation and evolution, environmental effects must be taken into account in order to gain a better understanding of galaxy evolution in the local universe.

tl;dr - Environmental effects should be considered in future models of galaxy formation and evolution.

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Address: Instituto de Física y Astronomía
         Universidad de Valparaíso
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