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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 ∼ 30). 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.
Highlights
The Hydrogen Epoch of Reionization Array (HERA; http:// reionization.org) is a staged experiment to use the redshifted 21 cm line of neutral hydrogen to characterize our Cosmic Dawn, from the formation of the first stars and black holes ∼0.1 Gyr after the Big Bang (z ∼ 30) through the full reionization of the intergalactic medium (IGM) ∼ 1 Gyr later (z ∼ 6)
As examined above, maximizing sensitivity to a limited number of spatial modes for the delay-spectrum technique requires a grid of antennas that simultaneously measures the same baselines using many redundant pairs of antennas. This redundancy may be exploited to calibrate the array as well, as long as the true antenna positions fall close enough to that ideal grid (Liu et al 2010). This technique was pioneered with the MIT EoR experiment (MITEoR) experiment (Zheng et al 2014), and has resulted in a package called OMNICAL developed for Precision Array Probing the Epoch of Reionization (PAPER) and HERA
As described in the previous section, the critical insights from the first generation 21 cm Epoch of Reionization (EOR) experiments have been applied to define the requirements for HERA—an instrument designed to ensure that foregrounds remain bounded within the wedge while delivering the sensitivity for high-significance detections of the 21 cm reionization power spectrum with
Summary
The Hydrogen Epoch of Reionization Array (HERA; http:// reionization.org) is a staged experiment to use the redshifted 21 cm line of neutral hydrogen to characterize our Cosmic Dawn, from the formation of the first stars and black holes ∼0.1 Gyr after the Big Bang (z ∼ 30) through the full reionization of the intergalactic medium (IGM) ∼ 1 Gyr later (z ∼ 6). These include the Precision Array Probing the Epoch of Reionization (PAPER; Parsons et al 2010), the Murchison Widefield Array (MWA; Tingay et al 2013), the LOw Frequency ARray (LOFAR; van Haarlem et al 2013), and the Long Wavelength Array (Ellingson et al 2009), as well as systems for existing dish arrays like the Very Large Array (Kassim et al 2013) and the Giant Metrewave Radio Telescope (GMRT; Paciga et al 2011).
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