Mathematics – Logic
Scientific paper
Sep 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003phdt.........9c&link_type=abstract
Thesis (PhD). ARIZONA STATE UNIVERSITY, Source DAI-B 64/03, p. 1285, Sep 2003, 149 pages.
Mathematics
Logic
3
Scientific paper
In the past decade, the Hubble Space Telescope (HST) has provided spectacular images of the most distant galaxies. This dissertation provides a foundation for understanding the nature of these faint galaxies. Historically, attempts to model the faint galaxy number counts have suggested that the luminosities of galaxies evolve over cosmic time, with the caveat that the models also underpredicted the bright end of the counts. This “normalization problem,” as it became known, is investigated here. The distribution of morphological types (ellipticals, spirals, irregulars) in the deepest HST fields indicated that, in contrast to the local Universe, the majority of the faintest galaxies are irregulars. This led to speculation that this normalization problem was type-dependent. The first part of this dissertation is a large HST survey aimed at addressing this issue. The results of this thirty field survey suggested that the normalization problem was larger for the irregulars and that these galaxies also showed the strongest signature of luminosity evolution. It was also clear that more data was needed to firmly draw detailed conclusions. The second part of the dissertation utilizes data from ground-based telescopes and is complementary to the HST work. This data allowed the galaxy counts as a function of morphological type to be extended to brighter flux levels, where the galaxies being studied are far enough away so that they are outside the local large-scale structure, but at low enough redshifts such that the effects of evolution will be minimized. The data, along with newly computed models, indicated that there really was not a normalization problem at all. This allowed for a simple study of the luminosity evolution of the faintest galaxies as seen by HST. The indication is that all types are evolving, with the irregulars showing the strongest amount of evolution. This claim is strengthened by the understanding of the normalization problem, or lack thereof, given in this dissertation. The study concludes with the exciting prospects for improving both the models and the data for this type of research with upcoming HST surveys.
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