The duration of reionization constrains the ionizing sources

TL;DR

This paper explores how the dominant galaxy types during reionization influence its duration, finding that bright galaxies likely played a major role, supported by observational constraints and CMB measurements.

Contribution

It compares models of reionization driven by faint versus bright galaxies, revealing that bright galaxies likely dominated, which affects the reionization timeline.

Findings

Bright galaxy models align better with observational constraints.

Faint galaxy models predict a longer reionization duration.

CMB measurements support bright galaxy dominance.

Abstract

We investigate how the nature of the galaxies that reionized the Universe affects the duration of reionization. We contrast two sets of models: one in which galaxies on the faint side of the luminosity function dominate the ionizing emissivity, and a second in which the galaxies on the bright side of the luminosity function dominate. The faint-end of the luminosity function evolves slowly, therefore the transition from mostly neutral to mostly ionized state takes a much longer time in the first set of models compared to the second. Existing observational constraints on the duration of this transition are relatively weak, but taken at face value prefer the model in which galaxies on the bright side play a major role. Measurements of the kinetic Sunyaev Zeldovich effect in the cosmic microwave background from the epoch of reionization also point in the same direction.