The First Galaxies: Chemical Enrichment, Mixing, and Star Formation

TL;DR

This study uses cosmological simulations to explore how the first galaxies formed, focusing on chemical enrichment, mixing, and star formation, revealing early stellar populations and conditions conducive to second-generation star formation.

Contribution

It introduces an efficient turbulent mixing algorithm in simulations to analyze chemical transport and star formation in the first galaxies, including effects of radiative feedback from Population III stars.

Findings

Most minihalos remain unaffected by supernovae or radiation.

Some minihalos are enriched and photoheated, leading to low-mass star formation.

The central galaxy contains cold, dense, enriched gas likely forming Population II stars.

Abstract

Using three-dimensional cosmological simulations, we study the assembly process of one of the first galaxies, with a total mass of 10^8 M_sun, collapsing at z = 10. Our main goal is to trace the transport of the heavy chemical elements produced and dispersed by a pair-instability supernova exploding in one of the minihalo progenitors. To this extent, we incorporate an efficient algorithm into our smoothed particle hydrodynamics code which approximately models turbulent mixing as a diffusion process. We study this mixing with and without the radiative feedback from Population III stars that subsequently form in neighboring minihalos. Our simulations allow us to constrain the initial conditions for second-generation star formation, within the first galaxy itself, and inside of minihalos that virialize after the supernova explosion. We find that most minihalos remain unscathed by ionizing radiation or the supernova remnant, while some are substantially photoheated and enriched to supercritical levels, likely resulting in the formation of low-mass Population III or even Population II stars. At the center of the newly formed galaxy, 10^5 M_sun of cold, dense gas uniformly enriched to 10^-3 Z_sun are in a state of collapse, suggesting that a cluster of Population II stars will form. The first galaxies, as may be detected by the James Webb Space Telescope, would therefore already contain stellar populations familiar from lower redshifts.