Dissertation
Studying the circumgalactic medium of massive galaxies at high redshift
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2026
Abstract
Galaxies are not isolated systems, but instead reside within extended gaseous structures that can span hundreds of kiloparsecs. This circumgalactic medium (CGM) serves as the interface between a galaxy’s interstellar medium (ISM) and the larger intergalactic medium (IGM), which connects galaxies along a cosmic web on megaparsec scales. It is within the CGM that key physical processes governing galaxy growth and evolution take place. In this work, we investigate these processes by performing integral field spectroscopy of massive galaxies at $z\sim2-3$ to map the diffuse cool gas via its \Lya\ emission. We report the detection of a cool gas stream accreting onto the hot halo of a dusty starburst galaxy, providing direct evidence of gas inflow from the cosmic web. As these systems evolve, the central supermassive black hole (SMBH) can transition into an active phase, driving feedback that expels gas and dust from the ISM into the CGM and giving rise to an unobscured quasar. Concurrently, the cold gas reservoir that fuels star formation becomes depleted within the host galaxy. We find that the \Lya\ emission associated with these systems is systematically fainter than that observed around typical quasars, suggesting that the CGM properties are closely linked to the evolutionary stage of the host galaxy. Motivated by this, we propose a scenario in which the interplay between quasar activity and the availability of cool gas within the CGM leads to a peak in \Lya\ luminosity at a characteristic stage in the evolutionary sequence. These results provide new insight into the origin and diversity of extended \Lya\ nebulae and their connection to galaxy evolution.
Details
- Title: Subtitle
- Studying the circumgalactic medium of massive galaxies at high redshift
- Creators
- Kevin Hall
- Contributors
- Hai Fu (Advisor)Ken Gayley (Committee Member)David Nataf (Committee Member)Greg Rudnick (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Physics
- Date degree season
- Spring 2026
- Publisher
- University of Iowa
- Number of pages
- xiv, 150 pages
- Copyright
- Copyright 2026 Kevin Hall
- Language
- English
- Date submitted
- 04/28/2026
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (page 140-150).
- Public Abstract (ETD)
One of the outstanding problems in extragalactic astronomy is understanding how galaxies grow and evolve over time. In general, galaxies must accumulate gas from their surroundings to provide the raw material needed for new stars to form. This large environment is known as the circumgalactic medium. For massive galaxies, much of this gas can be extremely hot, meaning it takes a long time to cool and condense into new stars. In this thesis, we begin by investigating a particular type of galaxy known as a starburst galaxy, which forms stars at an exceptionally high rate, equivalent to about 1000 stars the mass of our Sun every year. For comparison, the Milky Way forms roughly one such star per year. Using a technique called integral field spectroscopy, we detect evidence of a stream of cool, relatively pristine gas owing through the circumgalactic medium toward the starburst galaxy by capturing the Hi Lyman-Alpha emission line. This provides an important clue for how massive galaxies can sustain such intense periods of star formation.
Another key question is how these starburst galaxies evolve over time. One possibility is that the supermassive black hole at the center of the galaxy becomes active, forming a bright, energetic accretion disk. These galaxies, which are referred to as quasars, can drive powerful outflows, expelling gas and dust from the galaxy into the surrounding circumgalactic medium. The composite galaxies may represent a key evolutionary stage in their development. We find that the extended gas surrounding these galaxies is may be linked to their stage of evolution. In particular, the emission within the circumgalactic medium is typically fainter in systems that are transitioning into or hosting an active quasar than in more typical quasar systems. Building on these results, we introduce a simple toy model to explain the link between the evolutionary stage of the host galaxy and the observed emission from the circumgalactic medium.
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9985177174402771
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