  Using a high resolution cosmological simulation of reionization we have
examined the differing structures formed by gas and dark matter at a redshift
of 5.1. Baryon-rich regions form a small number of filaments, which connect the
largest galaxies in the simulation. More detailed examination of the ten
largest galaxies reveals long, slender gaseous filaments about 5 proper kpc in
width radiating from the galaxy centers. Extending out from each filament are a
few smooth, thin, nearly planar gaseous sheets. By contrast, the dark matter
concentrates into quasi-spherical bodies. The results have implications for our
understanding of structure formation in the early universe and of the Lyman
alpha forest.
