Date of Award

Spring 2021

Degree Type



Physics and Astronomy

Director of Thesis

Varsha Kulkarni

First Reader

Monique Aller

Second Reader

Monique Aller


Interstellar dust in galaxies has a profound effect on the galaxies’ light output and apparent properties as well as on the physical processes connected to star formation. Therefore, to understand the true properties of the galaxies around us, it is important to understand the dust in those galaxies and compare it to the dust in our galaxy. To do this, we study the effects of dust on background quasars by analyzing interstellar reddening and extinction. It has been shown that many quasars look redder and dimmer than the average quasar when observing them from Earth, due to the dust in our line of sight. In this project, we analyze observed spectra of quasars with previously identified moderately strong gaseous absorbers along the sightline and compare them to a template quasar spectrum to see if the observed spectrum was dimmed or reddened by the dust in galaxies located along the line of sight. We do this by fitting the observed spectra to the characteristic quasar template spectrum combined with three different extinction curves representative of the Milky Way (���� = 3.08) , Large Magellanic Cloud (���� = 2.76), and Small Magellanic Cloud (���� = 2.74). Looking at the best fit ��(��−��) value and the smallest reduced ��2 value, we determine which extinction curve best fits the observed quasar’s continuum in the UV-optical part of the spectrum. It was found that most of the ��(��−��) values were negative and close to 0, which meant that there was not a lot of dust in the foreground of the quasars to cause reddening.

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© 2021, Fatima Elkhatib