The HETDEX Survey: Probing Neutral Hydrogen in the Circumgalactic Medium of ∼88,000 Lyα Emitters

We explore the neutral hydrogen (H i) gas around 1.9 < z < 3.5 Lyman alpha emitters (LAEs) from the Hobby-Eberly Telescope Dark Energy Experiment using faint Ly alpha absorption. This absorption is the result of H i in the halo of the LAE scattering Ly alpha photons from the integrated light of background galaxies along the line of sight. We stack millions of spectra from regions around similar to 88,000 LAEs, in order to focus on the physics of the gas at large radii. The extensive number of fiber spectra contributing to the stacks ensures a sufficient signal-to-noise ratio to detect the faint Ly alpha absorption, which would otherwise be buried within the noise. We detect absorption out to a projected similar to 350 kpc around an average LAE at z similar to 2.5. We use these results to create an empirical radial W lambda(Ly alpha) profile around LAEs. Comparison with numerical simulations reveals a profile similar to the empirical one within this region. Compared to previous studies, the profile is similar but modestly higher. We also outline a simple physical picture motivated by the observed trends in the data. We plan to quantify this radial profile as a function of redshift, local density, and Ly alpha luminosity, to explore the relationship between LAE environments and H i distribution.