Cosmological contribution from population III stars in ultracompact minihalos

TL;DR

This study explores how Population III stars in ultracompact minihalos influence cosmic reionization and constrains primordial power spectrum parameters using Planck data.

Contribution

It models the impact of Pop. III stars in UCMHs on reionization and derives constraints on UCMH properties and primordial power spectrum amplitude.

Findings

UCMH initial mass > 10^{8.4} M_sun is tightly constrained.

Primordial power spectrum amplitude  10^{-8} for scales k  50 Mpc^{-1}.

Reionization by z > 3 is consistent with the model.

Abstract

In this work, we investigate the effect of Population~III~(Pop.~III) stars in ultracompact minihalos~(UCMHs) on the cosmic ionization history using the Planck observation data. Although high-redshift astrophysics is not understood yet, UCMHs could host the Pop.~III stars like the halos formed in the standard structure formation scenario. Such Pop.~III stars would emit ionizing photons during their main sequence and facilitate cosmic reionization in high redshifts. To study their effects on the global ionization, we model the cosmic reionization evolution based on the ``tanh"-type reionization model which is expressed by $z_{\mathrm{reio}}$ with additional two parameters characterizing the initial mass of UCMHs and the number density of UCMHs. We implement the Monte Carlo Markov Chain analysis with the latest Planck observation data for our reionization model. As the result, we found that if the UCMH initial mass is larger than $10^{8.4}\mathrm{M}_{\odot}$, the number density of UCMHs is strictly limited. Then we obtained the constraint on the amplitude of the primordial power spectrum through the constraint on the UCMH number density like $\mathcal{A}_{\zeta}\lesssim 10^{-8}$ in the scales, $k\lesssim 50\mathrm{Mpc}^{-1}$, when we assume that the standard ``tanh"-type reionization occurs by $z=3$, so that we set $z_{\mathrm{reio}}>3$.