The Circumgalactic Neutral Hydrogen at Cosmic Noon

Yuguang Chen (Caltech)
Friday, March 5, 2021 - 2:00pm to 3:00pm

In this talk, I will present our new Lyman-alpha observations focusing on the circumgalactic medium of z~2 star-forming galaxies, in both absorption and emission using Keck-LRIS and KCWI.  For absorption, we use the spectra of ~3000 galaxies from the Keck Baryonic Structure Survey (KBSS) to assemble ~200,000 distinct foreground-background galaxy pairs. The ensemble of sightlines and foreground galaxies is used to construct a 2D map of the mean excess Lya optical depth 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 ~60 KBSS galaxies. Their Lya spectra in the CGM are compared to the galactic azimuthal angle. We find that the Lya emission is statistically symmetric down within 30 kpc, suggesting that the outflowing H I has no directional preference. Lastly, I will introduce CWITools, a python package for scientific analysis of IFU data.

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