Cosmic filaments in superclusters

Large-scale structure calculations show that modest overdensity filaments will connect clusters of galaxies and these filaments are reservoirs of baryons, mainly in gaseous form. To determine whether such filaments exist, we have examined the UV absorption line properties of three active galactic nuclei (AGNs) projected behind possible filaments in superclusters of galaxies; the AGNs lie within 3 Mpc of the center lines of loci connecting clusters. All three lines of sight show absorption in Lyalpha, Lybeta, and/or O VI at redshifts within about 1300 km s(-1) of the nearby galaxy clusters that would define the closest filaments. For one AGN, the absorption-line redshifts are close to the emission-line redshift of the AGN, so we cannot rule out self-absorption for this object. These absorption-line associations with superclusters are unlikely to have occurred by chance, a result consistent with the presence of cosmic filaments within superclusters.