PAPER-64 Constraints on Reionization: The 21cm Power Spectrum at z=8.4

TL;DR

This paper reports improved upper limits on 21cm emission from cosmic reionization at redshift 8.4, using an extended observing campaign with the PAPER array, which constrains reionization models and informs future experiments.

Contribution

It presents the most stringent upper limits to date on the 21cm power spectrum at z=8.4, utilizing enhanced calibration and analysis techniques over a longer observation period.

Findings

New 2σ upper limit on Δ²(k) of (22.4 mK)² at z=8.4

Three-fold improvement over previous limits

Supports constraints against extremely cold reionization scenarios

Abstract

In this paper, we report new limits on 21cm emission from cosmic reionization based on a 135-day observing campaign with a 64-element deployment of the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) in South Africa. This work extends the work presented in Parsons et al. (2014) with more collecting area, a longer observing period, improved redundancy-based calibration, optimal fringe-rate filtering, and improved power-spectral analysis using optimal quadratic estimators. The result is a new $2\sigma$ upper limit on $\Delta^{2}(k)$ of (22.4 mK)$^2$ in the range $0.15 < k < 0.5h\ {\rm Mpc}^{-1}$ at $z = 8.4$. This represents a three-fold improvement over the previous best upper limit. As we discuss in more depth in a forthcoming paper (Pober et al. 2015, in prep), this upper limit supports and extends previous evidence against extremely cold reionization scenarios. We conclude with a discussion of implications for future 21cm reionization experiments, including the newly funded Hydrogen Epoch of Reionization Array (HERA). $\textbf{The limits presented in this paper have been retracted: The erratum can be found in Appendix A.}$