CONFIRMATION OF WIDE-FIELD SIGNATURES IN REDSHIFTED 21 cm POWER SPECTRA

Abstract

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