Confirmation of Wide-Field Signatures in Redshifted 21 cm Power Spectra

TL;DR

This paper confirms the presence of a wide-field foreground signature, called the 'pitchfork', in high-redshift 21 cm power spectra, demonstrating improved detection with enhanced data sensitivity and discussing mitigation strategies for future instruments.

Contribution

The study provides the first high signal-to-noise confirmation of the pitchfork foreground signature in 21 cm power spectra and discusses antenna design strategies to suppress this effect in future arrays.

Findings

Confirmed the pitchfork signature with SNR > 10.

Improved data sensitivity through coherent averaging of snapshots.

Future antenna designs can suppress foreground leakage by ~40 dB.

Abstract

We confirm our recent prediction of the "pitchfork" foreground signature in power spectra of high-redshift 21 cm measurements where the interferometer is sensitive to large-scale structure on all baselines. This is due to the inherent response of a wide-field instrument and is characterized by enhanced power from foreground emission in Fourier modes adjacent to those considered to be the most sensitive to the cosmological H I signal. In our recent paper, many signatures from the simulation that predicted this feature were validated against Murchison Widefield Array (MWA) data, but this key pitchfork signature was close to the noise level. In this paper, we improve the data sensitivity through the coherent averaging of 12 independent snapshots with identical instrument settings and provide the first confirmation of the prediction with a signal-to-noise ratio > 10. This wide-field effect can be mitigated by careful antenna designs that suppress sensitivity near the horizon. Simple models for antenna apertures that have been proposed for future instruments such as the Hydrogen Epoch of Reionization Array and the Square Kilometre Array indicate they should suppress foreground leakage from the pitchfork by ~40 dB relative to the MWA and significantly increase the likelihood of cosmological signal detection in these critical Fourier modes in the three-dimensional power spectrum.