Exploring the z~2.3 Cosmic Web with 3D Lyman-Alpha Forest Tomography

The hydrogen Lyman-alpha forest absorption, seen along the line-of-sight to bright distant quasars, has been an important probe of the high-redshift (z>2) cosmic web. In recent years, we have conducted Keck observations targeted instead at the Ly-a forest absorption of z~2-3 star-forming galaxies at ~24mag. This allows us to measure Ly-a forest absorption across a grid of sightlines separated by only ~2-3Mpc/h in the transverse direction and perform a reconstruction of the 3D absorption field which traces the underlying cosmic web. I will describe our latest observations which detected a galaxy protocluster at z=2.44 in the COSMOS field, as well as a curious object that might be a progenitor for low-z compact galaxy groups. I will also describe simulation work forecasting the observability of high-redshift cosmic voids with our technique, as well as argue that we will be able to recover sheets and filaments of the z~2 cosmic web with large-volume surveys over the next few years.

Speaker: K. G. Lee, Lawrence Berkeley National Labs