A Quantitative Analysis of Star-Forming Galaxies at Intermediate Redshifts: Number Counts, Morphological Sequences, and Evolutionary Timescales

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A Quantitative Analysis of Star-Forming Galaxies at Intermediate Redshifts: Number Counts, Morphological Sequences, and Evolutionary Timescales

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Title: A Quantitative Analysis of Star-Forming Galaxies at Intermediate Redshifts: Number Counts, Morphological Sequences, and Evolutionary Timescales
Author: Voyer, Elysse Nicole
Abstract: How did local galaxies obtain their Hubble morphologies and to what effect did star formation drive the transformations of past galaxies into these Hubble types? To answer these questions, galaxies at different epochs must be untangled from deep imaging and pieced together to analyze their evolution over time. This thesis probes an epoch when the Universe experienced a sharp decline in star-formation-rate density ~4.6Gyr ago, i.e. intermediate redshifts (0.2<z<1.2). Multiwavelength data was used to detect and analyze rest-frame ultraviolet (UV) star-forming galaxies in order to to establish what types of galaxies were forming stars during this time, and detect evolution within and between these galaxies populations.First, an initial study on UV galaxies in the Hubble Ultra Deep Field (HUDF) is performed. A photometric catalog of 96 sources in first targeted space-based U-band image of the HUDF is produced. By matching this with other catalogs, optical photometry, redshifts, spectral types (STs), and visual morphologies are obtained. This reveals that the majority of galaxies have spiral visual morphologies that are split between STs of late-type spirals and starburst galaxies. When compared to more distant star-forming Lyman Break Galaxies (LBGs) and their local counterparts, the sample is 14% less luminous. No evolution is detected in the overall galaxy sizes, however sub-galactic clumps are found to increase in size by a factor of 2-3.5 from high- to intermediate-z.Expanding upon this study, a sample of 333 far-UV (FUV) sources are detected in imaging of Great Observatories Origins Deep Survey -North and -South fields. FUV number counts are measured, covering 4 times larger area than the most recent study at these wavelengths (1610Å) and magnitudes (21-29), reducing cosmic variance effects. Moreover, the extragalactic background light was measured and found unlikely to be greater than 100 photons/cm^2/s/sr/Å.Finally, an analysis of the optical morphologies of the FUV sample is presented based on measurements of their STs and light profiles as a function of radius (Sérsic index). Results show star formation was primarily occurring in disk and merger morphologies over 0.1<z<1.2. Additionally, galaxies with irregular and spiral STs demonstrate a good correlation with Sérsic index.
Description: Degree awarded: Ph.D. Physics. The Catholic University of America
URI: http://hdl.handle.net/1961/9751
Date: 2011-06-24


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