Hydrogen Epoch of Reionization Array (HERA)

TL;DR

HERA is a large radio interferometer array designed to measure 21 cm emission from the early universe, aiming to understand cosmic reionization, the formation of the first galaxies, and the Epoch of Reionization with high sensitivity and advanced foreground mitigation.

Contribution

This paper details the design, scientific goals, and performance requirements of HERA, a new 350-element array for 21 cm cosmology, advancing observational capabilities in this field.

Findings

HERA's design meets performance requirements for foreground mitigation.

Forecasts indicate HERA will significantly improve constraints on reionization.

Current instruments are nearing sensitivity limits, and HERA aims to surpass them.

Abstract

The Hydrogen Epoch of Reionization Array (HERA) is a staged experiment to measure 21 cm emission from the primordial intergalactic medium (IGM) throughout cosmic reionization ($z=6-12$), and to explore earlier epochs of our Cosmic Dawn ($z\sim30$). During these epochs, early stars and black holes heated and ionized the IGM, introducing fluctuations in 21 cm emission. HERA is designed to characterize the evolution of the 21 cm power spectrum to constrain the timing and morphology of reionization, the properties of the first galaxies, the evolution of large-scale structure, and the early sources of heating. The full HERA instrument will be a 350-element interferometer in South Africa consisting of 14-m parabolic dishes observing from 50 to 250 MHz. Currently, 19 dishes have been deployed on site and the next 18 are under construction. HERA has been designated as an SKA Precursor instrument. In this paper, we summarize HERA's scientific context and provide forecasts for its key science results. After reviewing the current state of the art in foreground mitigation, we use the delay-spectrum technique to motivate high-level performance requirements for the HERA instrument. Next, we present the HERA instrument design, along with the subsystem specifications that ensure that HERA meets its performance requirements. Finally, we summarize the schedule and status of the project. We conclude by suggesting that, given the realities of foreground contamination, current-generation 21 cm instruments are approaching their sensitivity limits. HERA is designed to bring both the sensitivity and the precision to deliver its primary science on the basis of proven foreground filtering techniques, while developing new subtraction techniques to unlock new capabilities. The result will be a major step toward realizing the widely recognized scientific potential of 21 cm cosmology.