Signatures of reionization feedback in the near-infrared background

TL;DR

This paper proposes a new method to detect reionization feedback effects by analyzing the near-infrared background, focusing on the color and scale signatures caused by quenched faint galaxies in the early universe.

Contribution

It introduces a novel observational signature of reionization feedback based on galaxy color and scale dependence in the near-infrared background, distinguishable from other effects.

Findings

Reionization feedback induces a measurable color and scale signature in the near-infrared background.

Differences in the background persist up to 5 micrometers, detectable by upcoming missions like SPHEREx.

Power spectra of intensity ratio maps show significant variations, useful for future studies.

Abstract

The reionization of the intergalactic medium at redshifts $z\gtrsim 6$ is expected to have a lasting impact on galaxies residing in low-mass dark matter halos. Unable to accrete or retain gas photo-heated to temperatures $T \gtrsim 10^4$ K, the star formation histories of faint galaxies in the early Universe are expected to decline as they exhaust their gas supply, resulting in a turn-over in the galaxy luminosity function (LF) and a potential solution to the missing satellites problem in the local group. Unfortunately, there are several challenges to constraining `reionization feedback' empirically, most notably that galaxies in low-mass halos are intrinsically faint, and that there are other physical mechanisms capable of inducing a turn-over in the LF. In this work, we investigate a new signature of reionization feedback that is in principle distinct from other processes: as faint galaxies are quenched by reionization, their stellar populations passively age and grow redder while the brighter galaxies nearby continue to form stars at an increasing rate and so remain relatively blue. We find that this contrast, between quenched and un-quenched galaxies induces a scale and colour-dependent signature in the present-day near-infrared background comparable to the expected sensitivity of NASA's upcoming SPHEREx mission. Whereas models with pure mass suppression largely affect the signal at wavelengths $\lesssim 2 \mu\rm{m}$, $\sim 5$%-level differences in the background persist out to $\sim 5 \mu\rm{m}$ for reionization feedback models. Finally, the power spectra of intensity ratio maps exhibit larger variations, and may thus be a promising target for future analyses.