Date of Award

Spring 1-1-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Astrophysical & Planetary Sciences

First Advisor

James Green

Second Advisor

John Stocke

Third Advisor

Matthew Beasley

Abstract

I designed, built, tested and launched a sounding rocket payload to study the far-ultraviolet radiation of M51 (the Whirlpool Galaxy). This instrument, the Far-ultraviolet Imaging Rocket Experiment (FIRE, all acronyms are listed in Appendix B), produced the first ever astronomical image of 900-1000 Å light. It was designed to look at star forming regions in nearby galaxies by imaging the youngest, hottest O-type stars. Quantifying and locating the star forming regions within galaxies will directly aid galactic formation models. In addition, with the combination of the GALEX two-color images, FIRE was designed to investigate the intervening dust that significantly obscures these wavelengths. Since the accurate correction for dust is vital to measurements across the ultraviolet regime, improving dust extinction models aids a wide variety of both galactic and extra-galactic observations. Finally, FIRE demonstrated the successful use of two novel technologies, a silicon carbide imaging mirror and a pure indium filter.

In addition to FIRE, I also examined the absorption of neutral hydrogen in the intergalactic medium (IGM) along quasi-stellar objects (QSO) sightlines. The IGM is expected to contain a significant fraction of baryons at all epochs, but is difficult to detect and map since it is diffuse and emits radiation weakly. An ongoing IGM debate is whether clouds of gas detected through their Lyα absorption to QSOs are truly intergalactic or are extended halos of galaxies. A definitive answer would constrain estimates of baryonic density in the local universe and enhance our understanding of the formation of its structure. The CfA Great Wall of galaxies at redshifts of 0:015 < z < 0:03 offers an excellent locale to probe this question. This region is over-dense in galaxies and is surrounded by under-dense galactic voids, enabling us to compare absorbers' nearest galactic neighbors in highly contrasting density regions. I found 167 Lyα absorbers along eleven QSO sightlines and used a galaxy database to examine the Lyα absorber-galaxy relationship. I compare these results to previous publications and determine that Lyα absorbers and galaxies cannot trace the same large-scale structures at the megaparsec scale.

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