Galaxy Formation in Heavily Overdense Regions at z~10: the Prevalence of
  Disks in Massive Halos
  Using a high-resolution cosmological numerical simulation, we have analyzed
the evolution of galaxies at z~10 in a highly overdense region of the universe.
These objects could represent the high redshift galaxies recently observed by
the Hubble's WFC3, and be as well possible precursors of QSOs at z~6-7. To
overcome the sampling and resolution problems in cosmological simulations, we
have used the Constrained Realizations method. Our main result for z~10 shows
the region of 3.5h^{-1}Mpc radius in comoving coordinates completely dominated
by disk galaxies in the total mass range of >=10^9h^{-1}Mo. We have verified
that the gaseous and stellar disks we identify are robust morphological
features, capable of surviving the ongoing merger process at these redshifts.
Below this mass range, we find a sharp decline in the disk fraction to
negligible numbers. At this redshift, the disks appear to be gas-rich and the
dark matter halos baryon-rich, by a factor of ~2-3 above the average fraction
of baryons in the universe. The prevalence of disk galaxies in the high density
peaks during the epoch of reionization is contrary to the morphology-density
trend observed at low redshifts.
