Investigating Dust Attenuation Using Swift/UVOT Observations of Galaxies Over Cosmic Time

Restricted (Penn State Only)
- Author:
- Belles, Alexander
- Graduate Program:
- Astronomy and Astrophysics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 22, 2024
- Committee Members:
- Robin Ciardullo, Major Field Member
John Nousek, Major Field Member
Hyungsuk Tak, Outside Unit & Field Member
Michael Siegel, Major Field Member
Caryl Gronwall, Chair & Dissertation Advisor
Randy McEntaffer, Professor in Charge/Director of Graduate Studies
Joel Leja, Major Field Member - Keywords:
- interstellar dust
galaxy evolution
spectral energy distribution fitting - Abstract:
- In this dissertation, I will explore the topic of dust attenuation in galaxies, with particular interest on the variations seen in the ultraviolet (UV). Dust is interstellar material which preferentially extinguishes short wavelength light. In other galaxies, attenuation describes the net effects of dust in a complex geometry, where dust can extinguish and scatter light into the line of sight. Correcting for dust attenuation is vital as the UV, which is highly attenuated, probes recent star formation. Previous works have shown large variations in UV attenuation across the galaxy population. In order to understand the effects and variations in dust attenuation, two samples of nearby galaxies will be explored. To do so, data from the Ultraviolet Optical Telescope aboard the Neil Gehrels Swift Observatory are combined with other panchromatic photometry in the literature. Using spectral energy distribution fitting techniques, the best fit galaxy properties are derived for the SINGS/KINGFISH galaxies and the Local Volume Legacy sample. A large diversity in the shape of the UV attenuation curve is found, with evidence that the attenuation depends on how the time evolution of star formation within a galaxy is modelled. The measured star formation properties of the Local Volume are representative of the larger galaxy population. However, I show that standard techniques to correct for far-UV attenuation from the observed UV spectral slope overestimate the true amount of attenuation in low-mass galaxies. To demonstrate the impact uncertainty in the dust attenuation correction has on the study of galaxies, the star formation rate density evolution of a sample of galaxies as seen between 11.5 and 6.3 billion years after the Big Bang (redshift between 0.2<z<1.2) is measured using UVOT data. I find evolution consistent with previous works and discuss the complications involved in correcting for the effects of dust. Even with the additional UV data allowing for precise measurements of the UV spectral slope, I find a large spread in far-UV attenuation for galaxies at this epoch in cosmic time. Further, I find no trend in the UV spectral slope with UV luminosity or redshift, which are seen at higher redshift. Combined, these works show the importance of UV data and the choices made during spectral energy distribution fitting. Finally, I synthesize these results and place them within the larger context of extragalactic astrophysics, discuss potential future work, and explore the future of UV astrophysics.