Dissertation/Thesis Abstract

Investigating the Local and High Redshift Universe With Deep Survey Data and Ground-Based Spectroscopy
by Masters, Daniel Charles, Ph.D., University of California, Riverside, 2014, 183; 3618012
Abstract (Summary)

Large multiwavelength surveys are now driving the frontiers of astronomical research. I describe results from my work using data from two large astronomical surveys: the Cosmic Evolution Survey (COSMOS), which has obtained deep photometric and spectroscopic data on two square degrees of the sky using many of the most powerful telescopes in the world, and the WFC3 Infrared Spectroscopic Parallels (WISP) Survey, which uses the highly sensitive slitless spectroscopic capability of the Hubble Space Telescope Wide Field Camera 3 to detect star-forming galaxies over most of the universe's history. First I describe my work on the evolution of the high-redshift quasar luminosity function, an important observational quantity constraining the growth of the supermassive black holes in the early universe. I show that the number density of faint quasars declines rapidly above z ∼ 3. This result is discussed in the context of cosmic reionization and the coevolution of galaxies and their central black holes.

Next I present results of a multi-year campaign of near-infrared spectroscopy with FIRE, a world-class near-infrared spectrometer on the Magellan Baade 6.5 meter telescope in Chile, targeting emission-line galaxies at z ∼ 2 discovered with the Hubble Space Telescope. Our results showed that the typical emission-line galaxy at this redshift has low-metallicity, low dust obscuration, high ionization parameter, and little evidence for significant active galactic nucleus (AGN) contribution to the emission lines. We also find evidence that high redshift star-forming galaxies have enhanced nitrogen abundances. This result has interesting implications for the nature of the star formation in such galaxies – in particular, it could mean that a large fraction of such galaxies harbor substantial populations of Wolf-Rayet stars, which are massive, evolved stars ejecting large amounts of enriched matter into the interstellar medium.

Finally, I will discuss the discovery of three distant, ultracool brown dwarfs in the WISP survey. These objects, larger than massive planets but smaller than dwarf stars, are very difficult to detect, but their numbers and distribution in our galaxy have profound implications for our understanding of the formation of low-mass stars and planets. The brown dwarfs were found in the WFC3 grism spectroscopy, where they were identified through their strong atmospheric absorption features of water and methane. A systematic search for such objects in all WISP fields yielded three in total, allowing statistical inferences to be made regarding their distribution and number density in the Milky Way.

Indexing (document details)
Advisor: Mobasher, Bahram, McCarthy, Patrick
Commitee: Siana, Brian
School: University of California, Riverside
Department: Physics
School Location: United States -- California
Source: DAI-B 75/08(E), Dissertation Abstracts International
Subjects: Astrophysics, Astronomy
Keywords: Brown dwarf, Galaxy, High redshift, Quasar, Reionization, Starburst
Publication Number: 3618012
ISBN: 9781303859984
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