The intergalactic medium at reionization epoch and the circumgalactic medium

Abstract: I will introduce two of my past projects on the intergalactic medium (IGM) and circumgalactic medium (CGM). At redshift above 5-6, the IGM is believed to have gone through reionization, the era when the first stars and galaxies turned the gas from cold and neutral to hot and highly ionized. We show that the patchiness of the reionization process changes the shape of the post-reionization Lyman-alpha forest flux power spectrum. This imprint can be used to constrain models of reionization, and may also be a small contaminant to warm dark matter/fuzzy dark matter constraints. At much lower redshifts, the CGM has been a novel testbed for galaxy formation models, and yet the distribution of the CGM is still poorly constrained by observations. Using ~500 CHIME FRBs, we developed a weighted stacking scheme optimized for unlocalized FRBs and measured the excess dispersion measure induced by the CGM of <80 Mpc galaxies. We show that with our methodology and 2000-3000 more FRBs from CHIME, we will be able to detect foreground CGM at 4-sigma level and constrain CGM density models.