Tools, techniques, and early results in studies of 21 cm, Lyman-alpha, and H-alpha emission from the cosmic dawn

Abstract

We present advances in antenna characterization for low frequency radio observations of 21 cm emission from the Epoch of Reionization (EOR). Using satellite transmissions as probe signals, we map the all-sky, high dynamic range antenna response of the Murchison Widefield Array (MWA) and the Hydrogen Epoch of Reionization Array (HERA). We study deviations from numerical electromagnetic models and variation among the 128 MWA antenna elements, and show both effects severely limit foreground subtraction in the region of Fourier space where the EOR signal is brightest. We show that this contamination can be mitigated by modeling the observed foreground leakage as covariance in the frequency dimension, then downweighting it using the optimal quadratic estimator of Liu & Tegmark and Dillon, Liu, & Tegmark. We assess the real world prospects of cross-correlation measurements between 21 cm, Lyman-a, and H-a emission from the EOR. We show that geometric effects produce percent-level correlations between low frequency radio fluxes and nearinfrared fluxes, and we set the first limit on the angular cross spectrum between 21 cm and Lyman-a emission from the EOR. We show that in the near term, higher resolution radio and near-infrared surveys such as LOFAR and the Dark Energy Survey can start to probe optimistic models of the EOR.