Dalcanton, Julianne JByler, Eleanor2018-04-242018-04-242018-04-242017Byler_washington_0250E_18203.pdfhttp://hdl.handle.net/1773/41683Thesis (Ph.D.)--University of Washington, 2017A galaxy's spectrum is the sum of light emitted by stars and gas, modulated by intervening dust. Translating between the observed flux from galaxies and meaningful astrophysical quantities relies on ``stellar population synthesis'' (SPS) models. These models include descriptions for the light produced by stars and dust in galaxies, but most neglect the nebular emission from ionized gas. Accounting for nebular emission is important, as both line and continuum emission can contribute significantly to the total observed flux. The goal of this thesis is to include and exploit a proper accounting of emission from ionized gas in widely-used galaxy models. I have integrated a fully self-consistent treatment of nebular line and continuum emission into the SPS code Flexible Stellar Population Synthesis (FSPS; Conroy et al. 2009), using the photoionization code CLOUDY (Ferland et al. 2013). This model, CloudyFSPS, successfully reproduces observed properties of galaxies in the UV and optical wavelength regimes, and galaxies with young and old stellar populations. This thesis contains three main efforts. The first describes the development and validation of the CloudyFSPS package. The second uses CloudyFSPS to assess UV emission and absorption line diagnostics. The third uses CloudyFSPS to explore the origin of LIER-like emission and the UV-upturn in early-type galaxies.application/pdfen-USnoneabundancesgalaxiesISMstar formationultravioletAstronomyAstrophysicsAstronomyThesis