Unusually Large Fluctuations in the Statistics of Galaxy Formation at High Redshift

We show that various milestones of high-redshift galaxy formation, such asthe formation of the first stars or the complete reionization of theintergalactic medium, occurred at different times in different regions of theuniverse. The predicted spread in redshift, caused by large-scale fluctuationsin the number density of galaxies, is at least an order of magnitude largerthan previous expectations that argued for a sharp end to reionization. Thiscosmic scatter in the abundance of galaxies introduces new features that affectthe nature of reionization and the expectations for future probes ofreionization, and may help explain the present properties of dwarf galaxies indifferent environments. The predictions can be tested by future numericalsimulations and may be verified by upcoming observations. Current simulations,limited to relatively small volumes and periodic boundary conditions, largelyomit cosmic scatter and its consequences. In particular, they artificiallyproduce a sudden end to reionization, and they underestimate the number ofgalaxies by up to an order of magnitude at redshift 20.Comment: 8 ApJ pages, 4 figures, ApJ. Minor changes in revised version. Originally first submitted for publication on Aug. 29, 200