In an article now in press at the Astrophysical Journal, lead by HETDEX Graduate student Dongsheng Sun from the University of Tokyo, demonstrates how neutral hydrogen and HETDEX galaxies interplay. Using the Lyman-alpha forest absorptions of 14,736 background quasars from the Sloan Digital Sky Survey they create a 3D map of neutral hydrogen. This covers an area of 837 square degrees at redshifts z=2-3. By comparing the maps to galaxies and AGN identified by the Hobby-Eberly Telescope Dark Energy eXperiment and SDSS surveys, they measured their average radial profiles and line-of-sight profiles.

The team find that neutral hydrogen around AGN is higher than that around galaxies. This could suggest that the dark matter halos of AGN are more massive than those of lower mass, star-forming galaxies. The team observed weak absorption outskirts beyond neutral hydrogen structures of galaxies and AGN in the line-of-sight profiles that could be explained by the neutral hydrogen gas falling towards the source positions.