Honors College Theses

Publication Date



Physics (B.S.P.)

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Faculty Mentor

Dr. Monique Aller


Interstellar dust is an important component in many physical galactic processes, from star formation to heating and cooling mechanisms. The observed appearance of a galaxy may be altered by its dust content, due to the obscuring and reddening effects of dust. The chemical composition of dust in the interstellar medium of a galaxy can be determined through its absorption signature in the spectrum of a luminous background object, such as a quasar. A quasar absorption system is produced when the sightline to a quasar passes through or near a foreground, distant galaxy. Using the infrared 9.7µm and 18µm absorption features produced by quasar absorption systems, we can study silicate dust grain properties in these galaxies, including their optical depth and chemical composition. Variations in grain properties can then be explored from galaxy to galaxy. We discuss an analysis of data obtained as part of a program using Spitzer Space Telescope infrared spectra of quasars with known gas absorption systems. We explored several methods for analyzing these data, in particular testing different techniques for the background subtraction, the identification and removal of bad pixels, and the extraction and combination of individual spectra. In comparing these results, both for the galaxy M51 and for the quasar absorption system QSO0121+0027 (z=1.388), we find that the SMART algorithm yields the most stable results. For QSO0121+0027, the first system analyzed, we find no evidence of significant silicate dust absorption at 10μm, despite a strong carbonaceous dust signature, suggesting possible differences in grain formation.