The transition from population III to population II-I star formation

TL;DR

This study uses cosmological simulations to explore how the first metal-free stars transitioned to metal-rich star formation, highlighting the rapid enrichment and short-lived nature of Population III stars.

Contribution

It provides the first detailed simulation-based analysis of the transition from Population III to Population II-I star formation, including molecular evolution and metal enrichment processes.

Findings

Metal enrichment is patchy with unpolluted regions surviving at all redshifts.

Population III stars last for about 10 million years before transitioning.

The contribution of Population III stars to star formation drops below 1% rapidly.

Abstract

We present results from the first cosmological simulations which study the onset of primordial, metal-free (population III), cosmic star formation and the transition to the present-day, metal-rich star formation (population II-I), including molecular (H$_2$, HD, etc.) evolution, tracing the injection of metals by supernov{\ae} into the surrounding intergalactic medium and following the change in the initial stellar mass function (IMF) according to the metallicity of the corresponding stellar population. Our investigation addresses the role of a wide variety of parameters (critical metallicity for the transition, IMF slope and range, SN/pair-instability SN metal yields, star formation threshold, resolution, etc.) on the metal-enrichment history and the associated transition in the star formation mode. All simulations present common trends. Metal enrichment is very patchy, with rare, unpolluted regions surviving at all redshifts, inducing the simultaneous presence of metal-free and metal-rich star formation regimes. As a result of the rapid pollution within high-density regions due to the first SN/pair-instability SN, local metallicity is quickly boosted above the critical metallicity for the transition. The population III regime lasts for a very short period during the first stages of star formation ($\sim 10^7\,\rm yr$), and its average contribution to the total star formation rate density drops rapidly below $\sim 10^{-3}-10^{-2}$.