Reionization in the Light of Dark Stars

TL;DR

This paper explores how Dark Stars influence cosmic reionization and CMB optical depth, demonstrating that their inclusion allows higher Pop III star formation efficiencies to match Planck measurements.

Contribution

It introduces a semi-analytic model incorporating Dark Stars and feedback effects, showing their significant role in matching observed CMB optical depth.

Findings

Dark Stars can significantly impact reionization history.

Including Dark Stars allows higher Pop III star formation efficiencies.

Model aligns with Planck's measured optical depth.

Abstract

We investigate the effect of Dark Stars (DSs) on the reionization history of the Universe, and the interplay between them and feedback due to Lyman-Werner (LW) radiation in reducing the Cosmic Microwave Background (CMB) optical depth to a value within the $\tau = 0.054 \pm 0.007$ range measured by Planck. We use a semi-analytic approach to evaluate reionization histories and CMB optical depths, which includes Population II (Pop II) stars in atomic cooling halos and Pop III stars in minihalos with LW feedback, preceded by a DS phase. We show that while LW feedback by itself can reduce the integrated optical depth to the last scattering surface to $\sim 0.05$ only if the Pop III star formation efficiency is less than $\sim 0.2\%$, the inclusion of a population of DSs can naturally lead to the measured CMB optical depth for much larger Pop III star formation efficiencies $\gtrsim 1\%$.