A novel multi-scale analysis to determine red giant branch metallicities of Milky Way dwarf spheroidal galaxies

Through the last century the color-magnitude diagram has given a huge wealth of information about resolved stellar populations. Objects ranging from sparse star associations and open clusters to the massive spiral and elliptical galaxies have been measured in a wide array of photometric filter systems to understand how galaxies formed into the structure that we as humans see them as today. With a basic knowledge of nuclear physics fused with stellar evolution we have measured the ages of these systems of stars, along with estimates of the chemical abundances. Our understanding has been that smaller systems like open and globular star clusters were formed as a single population of stars at roughly the same time. In contrast the larger systems like spiral and elliptical galaxies were formed by a combination of constant star formation along with mergers of smaller proto systems. In fact, these mergers are still happening in the current epoch of the universe.;Over the last decade higher resolution studies paved by larger 8-10 meter telescopes, along with the orbiting Hubble Space Telescope, have shown the simplistic view of the formation of globular clusters and dwarf galaxies is no longer acceptable. Photometric and spectroscopic observations show that the globular clusters and dwarf spheroidal galaxies have multiple populations that vary with age, and/or metallicity (Geisler et al. 2007, Tolstoy et al. 2009). Two objects that show the extremes of each are the Carina dwarf spheroidal galaxy (Hurley-Keller et al. 1998) and the massive o Centauri globular cluster (Sollima et al. 2005). The more massive globular clusters show hints of multiple populations such as the NGC2808 globular cluster. It seems as though our understanding of the universe has only begun as we uncover more complexities with better tools to probe the universe.;This dissertation thesis brings a new tool for stellar population studies when analyzing data from photometric systems. I have chosen theM I, (U--R)0 color-magnitude diagram plane as a way to roughly calculate metallicities of red giant branches in old, metal poor, complex stellar populations. For MI = 0, -1, and -2, I produce histograms in a discrete multi-scale method to uncover blended sub-populations within the red giant branches. I use the massive globular cluster, o Centauri, as a test population to show the soundness of the method. Then the method is used to uncover a second possible sub-population in both the Draco and Ursa Minor dwarf spheroidal galaxies for the first time.