Constraint on Matter Power Spectrum on $10^6-10^9M_\odot$ Scales from ${\large\tau_e}$

TL;DR

This paper uses reionization observations and Planck data to set new constraints on the matter power spectrum at small scales, impacting dark matter models such as warm dark matter and sterile neutrinos.

Contribution

It introduces a novel method linking reionization physics to matter power spectrum constraints on $10^6-10^9M_ extodot$ scales, providing the strongest limits to date.

Findings

Upper limit on $ au_e$ constrains minimum mean free path of ionizing photons.

Derived lower bounds on warm dark matter particle mass and sterile neutrino mass.

Established confidence levels for dark matter particle mass limits.

Abstract

An analysis of the physics-rich endgame of reionization at $z=5.7$ is performed, utilizing jointly the observations of the Ly$\alpha$ forest, the mean free path of ionizing photons, the luminosity function of galaxies and new physical insight. We find that an upper limit on ${\rm \tau_e}$ provides a constraint on the minimum mean free path (of ionizing photons) that is primarily due to dwarf galaxies, which in turn yields a new and yet the strongest constraint on the matter power spectrum on $10^6-10^9M_\odot$ scales. With the latest Planck measurements of ${\rm \tau_e = 0.055 \pm 0.009}$, we can place an upper limit of $(8.9\times 10^6, 3.8\times 10^7, 4.2\times 10^8)M_\odot$ on the lower cutoff mass of the halo mass function, or equivalent a lower limit on warm dark matter particle mass ${\rm m_x \ge (15.1, 9.8, 4.6)keV}$ or on sterile neutrino mass ${\rm m_s \ge (161, 90, 33)keV}$, at $(1, 1.4, 2.2)\sigma$ confidence level, respectively.