Author ORCID Identifier
https://orcid.org/0009-0004-9126-8260
Date of Award
Spring 6-10-2026
Document Type
Thesis (Undergraduate)
Department
Physics and Astronomy
First Advisor
Ryan C. Hickox
Abstract
The detection of large-scale extended Lyman-α halos around galaxies at redshift z~2-3 has enabled the study of the circumgalactic medium (CGM) in emission. The CGM, a large reservoir of gas surrounding galaxies, plays a crucial role in the baryon cycle that drives the evolution of galaxies, as it lies at the interface between the cosmic web and galactic gas flows. Galaxies hosting active galactic nuclei (AGN) are of particular interest, as their powerful ionizing radiation drives mechanical and radiative feedback that alters the environment of their host galaxy. Redshift z~2-3, "cosmic noon", was one of the most active periods in the Universe's history, during which star formation activity and black hole growth peaked. Thus, the interplay between AGN and their host environment during this period is crucial for understanding the feedback mechanisms that produced the observed decline in global star formation shortly after z~2. The advent of the Keck Cosmic Web Imager (KCWI) and other highly sensitive integral field spectrographs (IFS) capable of detecting the faint, diffuse light from the CGM has reshaped our ability to study large-scale galactic environments and the gas flows that feed them. Using data from KCWI, this work examines the CGM around obscured (narrow-line) AGN at z~2-3. Using a tailored algorithm, kinematic maps of the extended nebular emission are produced, demonstrating the diverse properties of the ionized gas surrounding these objects. In order to constrain the resonant nature of the Lyman-α line, ancillary data in the K-band from the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) is used to measure the flux ratio of the two lines, to test against theoretical predictions from Case B recombination. Given the large extent of these nebulae, a spatially resolved flux ratio is measured along the spatial axis of the longslit observations, demonstrating variability in the relative strength of both lines.
Recommended Citation
Mendez, Ricardo Juan, "Characterizing the Circumgalactic Medium around z~2-3 Active Galactic Nuclei with Integral Field Spectroscopy" (2026). Physics and Astronomy Undergraduate Senior Theses. 6.
https://digitalcommons.dartmouth.edu/physics_senior_theses/6
