The formation of Milky Way-mass disk galaxies in the first 500 million years of a cold dark matter universe

TL;DR

This study uses large-scale hydrodynamic simulations to predict that the earliest massive galaxies in a cold dark matter universe formed with extensive disks, which could be observed by future telescopes to test cosmological models.

Contribution

First hydrodynamic simulation large enough to resolve early galaxy disks, predicting their prevalence and properties at high redshift.

Findings

70% of galaxies with stellar mass ≥10^10 M_sun at z=8-10 are disk galaxies

High-redshift galaxies are smaller, denser, and more gas-rich than low-redshift counterparts

Simulations predict early massive disk galaxies detectable by future telescopes

Abstract

Whether among the myriad tiny proto-galaxies there exists a population with similarities to present day galaxies is an open question. We show, using BlueTides, the first hydrodynamic simulation large enough to resolve the relevant scales, that the first massive galaxies to form are %in fact predicted to have extensive rotationally-supported disks. Although their morphology resembles in some ways Milky-way types seen at much lower redshifts, these high-redshift galaxies are smaller, denser, and richer in gas than their low redshift counterparts. From a kinematic analysis of a statistical sample of 216 galaxies at redshift $z=8-10$ we have found that disk galaxies make up 70\% of the population of galaxies with stellar mass $10^{10} M_\odot$ or greater. Cold Dark Matter cosmology therefore makes specific predictions for the population of large galaxies 500 million years after the Big Bang. We argue that wide-field satellite telescopes (e.g. WFIRST) will in the near future discover these first massive disk galaxies. The simplicity of their structure and formation history should make possible new tests of cosmology.