Constraining the Epoch of Reionization With Highly Dispersed Fast Radio Bursts

TL;DR

This paper explores using high-redshift Fast Radio Bursts' dispersion measures to constrain the timing, duration, and morphology of the Epoch of Reionization, providing forecasts for observational capabilities.

Contribution

It introduces a method to use FRB dispersion measures as probes of the EoR's astrophysics and morphology, with forecasted constraints based on mock data.

Findings

100 high-z FRBs can rule out uncorrelated reionization at 68% credibility.

≥10^4 FRBs can rule out uncorrelated reionization at 95% credibility.

≥10^5 FRBs can constrain reionization duration and midpoint with high precision.

Abstract

The period in which hydrogen in the intergalactic medium (IGM) is ionized, known as the Epoch of Reionization (EoR) is still poorly understood. The timing and duration of the EoR is expected to be governed by the underlying astrophysics. Furthermore, most models of reionization predict a correlation between the density and ionization field. Here we consider using the mean dispersion measure (DM) of high redshift Fast Radio Bursts (FRBs) as a probe of the underlying astrophysics and morphology of the EoR. To do this, we forecast observational scenarios by building mock data sets of non-repeating FRBs between redshifts $8\leq z \leq 10$. It is assumed that all FRBs have accompanying spectroscopic redshift measurements. We find that samples of 100 high redshift FRBs, in the above mentioned narrow redshift range, can rule out uncorrelated reionization at $68\%$ credibility, while larger samples, $\geq 10^4$ FRBs, can rule out uncorrelated reionization at $95\%$ credibility. We also find 100 high redshift FRBs can rule out scenarios where the Universe is entirely neutral at $z = 10$ with $68\%$ credibility. Further with $\geq 10^5$ FRBs, we can constrain the duration $\Delta z$ of reionization (duration between mean ionized fraction 0.25 to 0.75) to $\Delta z = 2.0^{+0.5}_{-0.4}$, and the midpoint of reionization to $z = 7.8^{+0.4}_{-0.2}$ at $95\%$ credibility.