Measurement of the baryonic acoustic oscillation scale in 21 cm intensity fluctuations during the reionisation era

TL;DR

This paper investigates how 21cm intensity fluctuations during reionisation can be used to measure baryonic acoustic oscillations, assessing the impact of ionised regions on measurement precision and bias.

Contribution

It introduces a semi-numerical model to evaluate the effects of ionised regions on BAO measurements from 21cm data during reionisation.

Findings

BAO scale can be measured with 1.5% precision at z=6.5-7.5

No systematic bias in BAO measurement at z > 6.5

Reionisation model suggests feasible BAO detection with future arrays

Abstract

It has recently been suggested that the power spectrum of redshifted 21cm fluctuations could be used to measure the scale of baryonic acoustic oscillations (BAOs) during the reionisation era. The resulting measurements are potentially as precise as those offered by the next generation of galaxy redshift surveys at lower redshift. However unlike galaxy redshift surveys, which in the linear regime are subject to a scale independent galaxy bias, the growth of ionised regions during reionisation is thought to introduce a strongly scale dependent relationship between the 21cm and mass power spectra. We use a semi-numerical model for reionisation to assess the impact of ionised regions on the precision and accuracy with which the BAO scale could be measured using redshifted 21cm observations. For a model in which reionisation is completed at z~6, we find that the constraints on the BAO scale are not systematically biased at z > 6.5. In this scenario, and assuming the sensitivity attainable with a low-frequency array comprising 10 times the collecting area of the Murchison Widefield Array, the BAO scale could be measured to within 1.5 per cent in the range 6.5 < z < 7.5.