Research
The Early Universe Group focuses on observational studies of the first billion years of cosmic history. We use JWST and other cutting-edge facilities to investigate Lyman-alpha emission, galaxy physical properties, and the large-scale structure of reionization.
Reionization Sources
JWST observations indicate abundant ionizing-photon production during the epoch of reionization, but the escape fraction of Lyman-continuum photons remains uncertain. We use lower-redshift star-forming galaxies, lensed faint systems, and compact local analogs to calibrate observables that may predict ionizing-photon escape in reionization-era galaxies.
JWST Galaxies
In the JWST/ERS CEERS collaboration, I led the analysis of rest-frame UV-to-optical spectra for Lyman-alpha emitters at z > 7. We compared Lyman-alpha transmission and ionizing photon output to estimate ionized bubble sizes and interpret why Lyman-alpha can remain visible in a partly neutral IGM.
Machine Learning
We apply statistical modeling and machine-learning techniques to infer emergent Lyman-alpha emission, damping-wing absorption, and galaxy physical properties from large observational and simulated datasets. These tools help reconstruct the physical and spatial evolution of reionization.
Reionization Topology
Combining HST grism and Keck spectroscopy, we measured the Lyman-alpha equivalent-width distribution at z > 6 and found enhanced IGM transmission around UV-luminous galaxies. This supports a picture in which bright galaxies preferentially trace overdense, earlier-ionized regions.
Lyman-alpha Surveys
My doctoral thesis used Lyman-alpha spectroscopy to map the ionization state of the IGM near the end of reionization. This work developed statistical constraints on the neutral hydrogen fraction, discovered high-redshift Lyman-alpha emitters, and advanced our understanding of reionization topology.
Galaxy Evolution
Using HST imaging and spatially resolved stellar-population modeling, we found evidence for reduced specific star formation rates in the centers of massive galaxies at z = 4, possibly revealing early phases of bulge growth.
Earlier Work
During my master’s research at Yonsei University, I developed a dark-matter halo merger-tree builder for cosmological N-body simulations and used semi-analytic models to study environmental effects on galaxy assembly.