The Role of Radiation and Halo Mergers in Pop III Star Formation

TL;DR

This study investigates how radiation and halo mergers influence the formation of Population III stars during Cosmic Dawn, revealing new pathways and the importance of mergers in early star formation.

Contribution

It uncovers the role of major mergers in accelerating Pop III star formation and highlights the impact of radiation on molecular hydrogen recovery in primordial minihalos.

Findings

Minimum halo mass for collapse increases from 10^5 to 10^6 Msun after star formation.

Gas-rich mergers rapidly recover gas and promote star formation in evacuated halos.

Major mergers can accelerate Pop III star formation, contrary to previous beliefs.

Abstract

We present a study of the co-evolution of a population of primordial star-forming minihalos at Cosmic Dawn. In this study, we highlight the influence of individual Population III stars on the ability of nearby minihalos to form sufficient molecular hydrogen to undergo star formation. In the absence of radiation, we find the minimum halo mass required to bring about collapse to be ~10^5 Msun, this increases to ~10^6 Msun after two stars have formed. We find an inverse relationship between halo mass and the time required for it to recover its molecular gas after being disrupted by radiation from a nearby star. We also take advantage of the extremely high resolution to investigate the effects of major and minor mergers on the gas content of star-forming minihalos. Contrary to previous claims of fallback of supernova ejecta, we find minihalos evacuated after hosting Pop III stars primarily recover gas through mergers with undisturbed halos. We identify an intriguing type of major merger between recently evacuated halos and gas-rich ones, finding that these 'mixed' mergers accelerate star formation instead of suppressing it like their low redshift counterparts. We attribute this to the gas-poor nature of one of the merging halos resulting in no significant rise in temperature or turbulence and instead inducing a rapid increase in central density and hydrostatic pressure. This constitutes a novel formation pathway for Pop III stars and establishes major mergers as potentially the primary source of gas, thus redefining the role of major mergers at this epoch.