Characterizing Signal Loss in the 21 cm Reionization Power Spectrum: A Revised Study of PAPER-64

TL;DR

This study investigates how analysis choices cause signal loss in 21cm EoR power spectrum measurements, leading to revised upper limits from PAPER-64 data and improved understanding of error estimation.

Contribution

It identifies sources of signal loss in power spectrum estimation and provides a revised, higher upper limit for the 21cm power spectrum from PAPER-64 data.

Findings

Detailed analysis of signal loss mechanisms.

Revised higher upper limit for PAPER-64 21cm power spectrum.

Summary of previously unaccounted errors in error estimation.

Abstract

The Epoch of Reionization (EoR) is an uncharted era in our Universe's history during which the birth of the first stars and galaxies led to the ionization of neutral hydrogen in the intergalactic medium. There are many experiments investigating the EoR by tracing the 21cm line of neutral hydrogen. Because this signal is very faint and difficult to isolate, it is crucial to develop analysis techniques that maximize sensitivity and suppress contaminants in data. It is also imperative to understand the trade-offs between different analysis methods and their effects on power spectrum estimates. Specifically, with a statistical power spectrum detection in HERA's foreseeable future, it has become increasingly important to understand how certain analysis choices can lead to the loss of the EoR signal. In this paper, we focus on signal loss associated with power spectrum estimation. We describe the origin of this loss using both toy models and data taken by the 64-element configuration of the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER). In particular, we highlight how detailed investigations of signal loss have led to a revised, higher 21cm power spectrum upper limit from PAPER-64. Additionally, we summarize errors associated with power spectrum error estimation that were previously unaccounted for. We focus on a subset of PAPER-64 data in this paper; revised power spectrum limits from the PAPER experiment are presented in a forthcoming paper by Kolopanis et al. (in prep.) and supersede results from previously published PAPER analyses.