Galaxy formation in heavily overdense regions at z ∼ 10: The prevalence of disks in massive halos

Abstract

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 Wide Field Camera 3 and could as well be possible precursors of QSOs at z ∼6-7. To overcome the sampling and resolution problems in cosmological simulations of these rare regions, we have used the constrained realizations method. Our main result for z ∼10 shows the high-resolution central region of 3.5 h -1 Mpc radius in comoving coordinates being completely dominated by disk galaxies in the total mass range of ≳ 109 h -1 M ⊙. 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 compared to z = 0, and the dark matter halos baryon-rich, by a factor of ∼2-3 above the average fraction of baryons in the universe. The dominance of disk galaxies in the high-density peaks during the epoch of re-ionization is contrary to the morphology-density trend observed at low redshifts. © 2011 The American Astronomical Society. All rights reserved.