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Author ORCID Identifier


Open Access Dissertation

Document Type


Degree Name

Doctor of Philosophy (PhD)

Degree Program


Year Degree Awarded


Month Degree Awarded


First Advisor

Houjun Mo


In the current understanding of galaxy formation, galaxies are believed to form and evolve in dark matter halos. The dark matter halos are collapsed objects that form and grow via gravitational instability of small initial density fluctuation in the cosmic field. They are not only the hosts of galaxies but are tracers of the cosmic web of the Universe. They are thus crucial components for understanding how galaxies form and evolve within the cosmic web. This dissertation is a systematic investigation of the galaxies and gas in the dark matter halos and the cosmic web, using observation data of large galaxy surveys such as the Sloan Digital Sky Survey (SDSS), and of the Cosmic Microwave Background (CMB) survey such as the Planck, together with simulations and modellings for comparison and interpretation. Specifically, we have identified dark matter halos in the low-redshift Universe, and constructed the largest to date all-sky group catalog. We also investigated correlations between many of the galaxy and halo properties, particularly finding, for the first time, an observational proxy of halo age. Then, I developed a series of novel approaches to maximize the detection of the Sunyaev-Zel'dovich effect (SZE), and from it explored the gas properties in halos to find that the gas mass fraction even in Milky Way-size halos is about the cosmic mean fraction. The analysis identified the baryons in a warm-hot medium on halo scales. We also show that the thermal SZE can be used to constrain the mean relationship between thermal energy of IGM gas and local total matter density for the first time. We support the reliability of our methods and results with tests where the methods are applied to the mock CMB maps constructed from simulations. Finally, we present comparisons with simulations of the SZE, and discuss the implications for its constraining power of galaxy formation models.