Sean Johnson
Graduate Student, Department of Astronomy and Astrophysics

Location: ERC 526

Scientific Advisor: Hsiao-Wen Chen

Affiliations: Kavli Institute for Cosmological Physics

Publications: ADS | arXiv

Scientific Projects

Ph.D. Thesis Defense
Defense date: July 18, 2016
Ph.D. Thesis: "Studies of the relationship between galaxies and the inter/circum-galactic medium"

Scientific Advisor: Hsiao-Wen Chen
Ph.D. Committee members: Andrey Kravtsov, Rich Kron, John Mulchaey, and Don York.

"Sean's thesis work casts new light on the intricate physical processes that drive the baryon cycles between star-forming regions and the intergalactic space. He led an ambitious survey of the galactic environments around chemically-enriched gas revealed in strong absorption against a background source. Sean's thesis sample represents the first of its kind in terms of both the scale and depth of galaxy survey data in quasar fields. It provides a pathfinder for future large-scale studies that will combine wide-field galaxy surveys with absorption spectroscopy to advance our understanding of chemical enrichment in low-density regions away from galaxies."
- Hsiao-Wen Chen, PhD advisor

Thesis Abstract: Galaxies are thought to grow through star formation that is fueled by the accretion of gas in dark matter halos and from intergalactic space. In turn, star formation and active galactic nuclei drive outflows that regulate gas cooling and accretion while enriching the surrounding gas with heavy elements. The resulting enriched gaseous halos that surround galaxies are thought to dominate the baryon reservoirs capable of fueling future growth, and developing an empirical understanding of the relationship between galaxies and this surrounding gas consequently represents a key step toward a more complete understanding of galaxy evolution. The diffuse nature of galaxy halo gas renders direct emission too faint to be detected with current facilities except in extreme cases, but the gas can be readily observed as absorption features in the spectra of UV-bright background sources such as quasars. I will present a series of observational studies that provide new insights into the relationship between galaxies and surrounding diffuse baryon reservoirs through combined galaxy redshift and quasar absorption line surveys. The survey results highlight the role of galaxy environment and active galactic nuclei in galaxy evolution and their possible relation with extended halo gas reservoirs.

Department Committees
Past Department Committees:
  • Admissions: 2015 - 2016