2024 Physics Oral Defense: Probing UV Emission Surrounding Galaxies: Observational Studies and Telescope Instrumentation

Jessica Li, Physics Graduate Student



noon to 3 p.m., April 2, 2024

Abstract: The circumgalactic medium (CGM) and intergalactic medium (IGM), the tenuous gas surrounding galaxies represent a significant portion of matter in the universe as indicated by both theoretical and observational studies.  This faint and diffuse gas is not well studied since it is very challenging to observe.  Studying the CGM is essential for understanding astrophysical principles that govern the formation and evolution of stars and galaxies throughout the universe. It is believed to be the reservoir of gas and material that is both the source and regulator of star-forming fuel, controlling the exchange between the intergalactic medium (IGM) between galaxies and interstellar medium (ISM) within galaxies. This dissertation focuses on advancing our understanding of these processes through ultraviolet (UV) spectroscopic CGM emission line observations in high redshift galaxies in addition to instrumentation work for balloon-borne and space telescopes that target low redshift galaxies.  

This thesis describes four distinct but interrelated projects that combine observational astronomy, instrument building, and technology development. First, I analyzed data taken with the Palomar Cosmic Web Imager (PCWI) that observed the CGM around four different quasi-stellar object (QSO) or quasar pairs (z$\sim$2.3) during a period of peak star formation, cosmic noon.  I then used the data to map the Lyman-alpha (Ly$\alpha$) emission intensity, kinematics, and surface brightness as a function of distance from the brighter QSO of each pair.  Observations of galaxies throughout cosmic time serve as puzzle pieces in understanding galactic evolution.  This study adds to the growing archive of galactic emission line studies to pinpoint redshift specific characteristics that drive the behavior of star formation.  Second, I designed and built a new in-flight calibration system for the balloon-borne telescope FIREBall-2 (Faint Intergalactic-medium Redshifted Balloon) that flew in the September 2023 launch.  It was designed to observe Ly$\alpha$, O VI, C VI emission from the CGM of low redshift galaxies (z$\sim$0.3-1.0).  Third, I developed the grating prototype performance verification test setup and optical alignment procedure for the Aspera UV SmallSat mission which is designed to map the warm-hot coronal gas traced by O VI emission in nearby galaxy halos with a projected launch date of 2025.  Fourth, I developed a test setup and procedure for grating characterization of a small format grating sample and present preliminary measurement results.  This program focuses on advancing UV reflective grating technology for the next generation of high-resolution UV spectrographs.  Through a partnership with University of Iowa (UI), UV grating designs are optimized through optical simulations and manufactured before shipping to University of Arizona (UA) for grating characterization. Finally, I discuss the significance of these projects for UV astrophysics and instrumentation along with my future work.

Zoom: https://arizona.zoom.us/j/87486910099?pwd=a3Z0Y3A0MHpVbUx6ZkJKdFhXbUdkZz09  password 1420