PPT Slide
If the three QSO sight-lines are representative, then nearly all sight-lines through the cluster must intersect a neutral hydrogen cloud, and the neutral hydrogen mass of the cluster is .
This implies that the density of neutral hydrogen within this volume is 100 times greater than is typical at this redshift. If the “ghost cluster” model is correct this overdensity cannot be caused by excess baryons within this volume, as all volumes have roughly the same baryon density at this redshift. For some reason, the fraction of baryons that are in the neutral form must be greatly enhanced in the cluster.