The Absorption and Emission of Neutral Hydrogen around Star-Forming Galaxies at Cosmic Noon

Neutral hydrogen (H I) constitutes an important component of the circumgalactic gas. In this talk, my thesis presents two powerful samples from the Keck Baryonic Structure Survey (KBSS) that focus on the CGM Lya absorption and emission around z~2 star-forming galaxies. For absorption, we use the spectra of ~3000 galaxies to assemble ~200,000 distinct foreground-background galaxy pairs. The ensemble of sightlines and foreground galaxies is used to construct a 2D map of Lya absorption as a function of projected galactocentric distance (20–4000 kpc) and line-of-sight velocity. We compare the map with the cosmological zoom-in simulation and a simple two-component (inflow + outflow) analytical model. The comparisons suggest that galaxy-scale outflow dominates the H I kinematics within ~50 kpc, while infall and Hubble expansion dominate at >100 kpc. For emission, we obtain deep integral field unit observations on ~100 galaxies. Their Lya spectra in the CGM are compared to the galactic azimuthal angle. We find that the Lya emission is statistically symmetric within 30 kpc, suggesting that the outflowing H I has no directional preference. Intriguingly, however, the angular dependence of Lya emission prevails from low-Lya-emitting galaxies, indicating that stable angular momentum may start to establish among these galaxies. Lastly, I will present preliminary results on the connection between the CGM Lya emission and host galaxy properties.