Probing Large-Scale Structure of the Universe with the Canadian Hydrogen Intensity Mapping Experiment
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wang-hcwang96-phd-phys-2026-thesis.pdf
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Author(s)
Wang, Haochen
Advisor(s)
Masui, Kiyoshi
Date Issued
May 2026
Publisher
Massachusetts Institute of Technology
Abstract
Precision cosmology has dramatically advanced our understanding of the Universe over the past three decades, establishing the ΛCDM cosmological model. Despite the progress, roughly 90% of the universe's volume is still not observed, and about 50% of the baryons in the observed Universe remain unaccounted for. The lack of observations leaves many important questions unanswered, such as the nature of dark energy and the strength of galaxy feedback processes. Emerging radio interferometric experiments, like the Canadian Hydrogen Intensity Mapping Experiment (CHIME), can provide the missing observations to address the unresolved mysteries of the Universe. In this thesis, I present new data analysis techniques for CHIME to probe large-scale structure, enabling radio cosmological experiments to study dark energy and galaxy feedback.
CHIME can map out the cosmic matter distribution and constrain the dark energy equation of state by detecting the accumulated 21-cm line emissions from neutral hydrogen. To achieve this, CHIME must overcome the bright astrophysical foregrounds from the Milky Way. By combining traditional linear and nonlinear foreground filters, I have developed a new class of foreground filtering algorithm, called Hybrid Foreground Residual Subtraction (HyFoReS). Compared to traditional foreground filters, HyFoReS has the advantage of being more robust to systematics while preventing signal loss. Through simulations and applications to real CHIME data, I have shown that HyFoReS can suppress foreground contamination due to telescope systematics and enable the measurement of large-scale structure clustering statistics. CHIME is also the leading instrument for discovering fast radio bursts (FRBs). These millisecond-duration energetic radio transients show dispersive delays in their signal, quantified as the dispersion measure (DM), directly tracing ionized baryons along their lines of sight. The cosmic baryon distribution extracted from DM can serve as an important tool to understand galaxy feedback physics. In this thesis, I present the technique to cross-correlate FRB DM with galaxies in Fourier space to measure the cosmic baryon distribution. Using the Second CHIME/FRB Catalog, I made the first definitive detection of spatial correlations in FRB DM due to cosmic structure and placed constraints on the strength of galaxy feedback. The novel data analysis tools presented in this thesis have advanced radio cosmology and enabled future experiments to constrain physics from the unprobed regions of the Universe.
MIT Department
Massachusetts Institute of Technology. Department of Physics
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