Neutral hydrogen in cosmic voids.

Abstract

An unsuccessful search was conducted for H I clouds in two voids in the cosmic distribution of galaxies. The search employed the Green Bank 300-ft telescope, and was sensitive (at the 4sigma-level) to clouds of mass greater than about 10 to the 10th/sq h solar mass (assuming sizes less than about 100/h kpc and velocity spreads less than 100 km/s). Roughly 7 percent of the Perseus-Pisces void and 19 percent of the Hercules void were searched. It is concluded that the voids do not contain a cosmologically significant population of H I protogalaxies, and evidence consistent with the hypothesis that the voids are indeed regions of low matter density in the universe is summarized.