Gas in Simulations of High Redshift Galaxies and Minihalos
  We study the gas content of halos in the early universe using high resolution
hydrodynamical simulations. We extract from the simulations and also predict
based on linear theory the halo mass for which the enclosed baryon fraction
equals half of the mean cosmic fraction. We find a rough agreement between the
simulations and the predictions, which suggests that during the high-redshift
era before stellar heating, the minimum mass needed for a minihalo to keep most
of its baryons throughout its formation was $\sim 3 \times 10^4$ M$_\odot$. We
also carry out a detailed resolution analysis and show that in order to
determine a halo's gas fraction even to 20% accuracy the halo must be resolved
into at least 500 dark matter particles.
