The End of an Era - The Population III to Population II Transition and the Near Infrared Background

TL;DR

This paper explores how the spectrum of the Near Infrared Background can reveal details about the transition from Population III to Population II stars, especially through a predicted Lyman-alpha bump influenced by star properties and formation history.

Contribution

It introduces the concept of the Lyman-alpha bump as an observable signature of Population III stars in the Near Infrared Background and models its dependence on star mass, formation rate, and redshift.

Findings

A Lyman-alpha bump can indicate massive Population III stars at z < 15.

The bump's shape depends on star formation rate and transition times.

Presence of the bump suggests Population III stars may exist at z ~ 6 even if rare.

Abstract

There are only a few ways to constrain the Era of Reionization and the properties of high redshift (z>6) stars through observations. Here, we discuss one of these observables - the spectrum of the Near Infrared Background - and how it is potentially affected by the transition from Population III to Population II stars. The stronger Lyman-alpha emission expected from massive Population III stars could result in a 'bump' in the spectrum of the Near Infrared Background (referred to in this work as the Lyman-alpha bump). The strength and shape of this bump can reveal properties of Population III stars. The Lyman-alpha bump is predicted to be higher if Population III stars are more massive and present at lower redshifts. The shape of the bump is governed by the star formation rate and the time it takes Population III stars to transition to Population II stars. If Population III stars are indeed massive, a bump is predicted as long as Population III stars exist at z < 15, even if their star formation rate is as low as 10^-7 M_sun yr^-1 Mpc^-3. This means that there may be some observational signature in the Near Infrared Background of small pockets of metal-free gas forming Population III stars at z ~ 6, even if they are quite rare.