PAPER-64 CONSTRAINTS ON REIONIZATION: THE 21 cm POWER SPECTRUM AT<i>z</i>= 8.4

Abstract

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 $\\textbf{The\nlimits presented in this paper have been retracted: The erratum can be found in\nAppendix A.}$\n