Mathematics – Logic
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........10t&link_type=abstract
PhD Dissertation, Wyoming Univ. Laramie, WY United States
Mathematics
Logic
Globular Clusters, Spiral Galaxies, Visual Photometry, Astronomical Photometry, Galactic Radiation, Galactic Evolution, Luminosity, Galactic Halos
Scientific paper
Globular clusters (GC's) are well-ordered, compact groupings of stars, containing roughly 100,000 members confined to a spherical space several parsecs in diameter. They are probably a major component of every galaxy. The constituent stars are mostly metal-poor and old. The light from these objects is dominated by the emission from red giants and moderate-mass main sequence stars. About 200 GCs populate the halo of our Galaxy, showing a R1/4 falloff symmetric about the Galactic center. They may represent an earlier phase in the Milky Way's evolution, when it was still largely spherically symmetric and was only beginning to collapse to the disk seen today. These objects may be ancient even on universal time scales, constraining cosmological models of the age of the universe itself. They may comprise the closest and easiest way to study relics of the age when galaxies first formed. The Michigan State University Visual CCD Camera at the Wyoming Infrared Observatory was used to map the GC systems (GCS's) of several nearby spiral galaxies and to obtain four-filter visual photometry of the cluster's integrated light. This information will enhance our understanding of galaxy formation and the dynamics that govern galaxy evolution and allow us to explore the universality of the globular cluster luminosity function (GCLF) and its applicability to the question of the extragalactic distance scale. Three nearby, nearly edge-on spiral galaxies (NGC 4460, NGC 7640, and NGC 891) were examined. The observations confirmed the existence of GCSs in each galaxy and approached the peak of the GCLF, allowing determination of that peak using Gaussian fits. The colors were used to filter the initial point source list from each filter and to construct a GCS likelihood metric for each source, which enabled further filtering and the production of a ranked list of GC candidates for each galaxy. This metric's usefulness was confirmed using the Milky Way's GCS. The total GC population was inferred from the Gaussian fits and used to construct specific frequencies for these galaxies which were consistent with values for other galaxies of similar type and mass.
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