Galaxy Formation in Heavily Overdense Regions at z~10: the Prevalence of Disks in Massive Halos

TL;DR

This study uses high-resolution simulations to show that at redshift ~10, heavily overdense regions are dominated by gas-rich disk galaxies in massive halos, challenging low-redshift morphology-density trends.

Contribution

It demonstrates that in overdense regions at z~10, disk galaxies are prevalent in massive halos, providing new insights into early galaxy morphology during reionization.

Findings

Region dominated by disk galaxies in halos >=10^9h^{-1}Mo

Disks are robust and survive mergers at high redshift

High baryon fraction in disks and halos at z~10

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 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.