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ABSTRACT Population III stars are possible precursors to early supermassive black holes (BHs). The presence of soft UV Lyman–Werner (LW) background radiation can suppress Population III star formation in minihaloes and allow them to form in pristine atomic-cooling haloes. In the absence of molecular hydrogen ($$\rm H_2$$) cooling, atomic-cooling haloes enable rapid collapse with suppressed fragmentation. High background LW fluxes from preceding star-formation have been proposed to dissociate $$\rm H_2$$. This flux can be supplemented by LW radiation from one or more Population III star(s) in the same halo, reducing the necessary background level. Here, we consider atomic-cooling haloes in which multiple protostellar cores form close to one another nearly simultaneously. We assess whether the first star’s LW radiation can dissociate nearby $$\rm H_2$$, enabling rapid accretion on to a nearby protostellar core, and the prompt formation of a second, supermassive star (SMS) from warm, atomically-cooled gas. We use a set of hydrodynamical simulations with the code enzo, with identical LW backgrounds centred on a halo with two adjacent collapsing gas clumps. When an additional large local LW flux is introduced, we observe immediate reductions in both the accretion rates and the stellar masses that form within these clumps. While the LW flux reduces the $$\text{H}_2$$ fraction and increases the gas temperature, the halo core’s potential well is too shallow to promptly heat the gas to $$\gtrsim$$1000 K and increase the second protostar’s accretion rate. We conclude that this internal LW feedback scenario is unlikely to facilitate SMS or massive BH seed formation.
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The role of radiation and halo mergers in Pop III star formation
ABSTRACT We present a study of the co-evolution of a population of primordial star-forming minihaloes at Cosmic Dawn. In this study, we highlight the influence of individual Population III stars on the ability of nearby minihaloes 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 ∼105 M⊙, this increases to ∼106 M⊙ 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 minihaloes. Contrary to previous claims of fallback of supernova ejecta, we find minihaloes evacuated after hosting Pop III stars primarily recover gas through mergers with undisturbed haloes. We identify an intriguing type of major merger between recently evacuated haloes 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 haloes 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.
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- Award ID(s):
- 1835213
- PAR ID:
- 10472871
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 527
- Issue:
- 1
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 307-320
- Size(s):
- p. 307-320
- Sponsoring Org:
- National Science Foundation
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