First Results from HERA Phase I: Upper Limits on the Epoch of Reionization 21 cm Power Spectrum

Abstract

We report upper limits on the Epoch of Reionization 21 cm power spectrum at redshifts 7.9 and 10.4 with 18 nights of data (∼36 hr of integration) from Phase I of the Hydrogen Epoch of Reionization Array (HERA). The Phase I data show evidence for systematics that can be largely suppressed with systematic models down to a dynamic range of ∼109 with respect to the peak foreground power. This yields a 95% confidence upper limit on the 21 cm power spectrum of Δ 21 2 ≤ ( 30.76 ) 2 mK 2 at k = 0.192 h Mpc−1 at z = 7.9, and also Δ 21 2 ≤ ( 95.74 ) 2 mK 2 at k = 0.256 h Mpc−1 at z = 10.4. At z = 7.9, these limits are the most sensitive to date by over an order of magnitude. While we find evidence for residual systematics at low line-of-sight Fourier k ∥ modes, at high k ∥ modes we find our data to be largely consistent with thermal noise, an indicator that the system could benefit from deeper integrations. The observed systematics could be due to radio frequency interference, cable subreflections, or residual instrumental cross-coupling, and warrant further study. This analysis emphasizes algorithms that have minimal inherent signal loss, although we do perform a careful accounting in a companion paper of the small forms of loss or bias associated with the pipeline. Overall, these results are a promising first step in the development of a tuned, instrument-specific analysis pipeline for HERA, particularly as Phase II construction is completed en route to reaching the full sensitivity of the experiment.

Automated Detection of Antenna Malfunctions in Large‐N Interferometers: A Case Study With the Hydrogen Epoch of Reionization Array

“…Note that this data is from the second phase of the HERA array, which uses Vivaldi feeds rather than dipoles, along with other changes, and differs significantly from the phase one data analyzed in HERA Collaboration et al. (2021). The HERA receivers are distributed throughout the array in nodes which contain modules for post‐amplification, filtering, analog to digital conversion, and a frequency Fourier transform.…”

“…Next, we perform a simple RFI flagging, analogous to the algorithm used in HERA Collaboration et al. (2021), but performed on a single auto‐correlation waterfall averaged over all remaining antennas. This process includes a search for local outliers after median filtering and then mean filtering, which are flagged as RFI.…”

“…This is a simplified version of the algorithm used in HERA Collaboration et al. (2021) with the exception that it is sped up by performing it on a single waterfall averaged over unflagged antennas.…”

Snowmass2021 Cosmic Frontier White Paper: Cosmological Simulations for Dark Matter Physics

“…For example, energy released by annihilating or decaying DM can heat the intergalactic medium and contribute to reionization. Upcoming probes of the Epoch of Reionization (EoR), such as HERA [271] and SKA [261], therefore have the potential to provide a new window into DM microphysics.…”

Current status and future of cosmology with 21cm Intensity Mapping

“…LOFAR 13,14 and NenuFAR 15 have deployed antennae in Europe, LWA 16 is a large dipole array in New Mexico (USA), while MWA 17 or HERA 18,19 observe from Australia. Recent upper limits on the 21cm power spectrum from these experiments can be found in 20 for LOFAR, in 21 for MWA and in 22 for HERA. Detection of the 21cm EoR signal is also the main goal of the SKA-low instrument of the future SKA (Square Km Array) observatory 23 .…”