Direct Optimal Mapping for 21 cm Cosmology: A Demonstration with the Hydrogen Epoch of Reionization Array

Abstract

Motivated by the desire for wide-field images with well-defined statistical properties for 21 cm cosmology, we implement an optimal mapping pipeline that computes a maximum likelihood estimator for the sky using the interferometric measurement equation. We demonstrate this “direct optimal mapping” with data from the Hydrogen Epoch of Reionization (HERA) Phase I observations. After validating the pipeline with simulated data, we develop a maximum likelihood figure-of-merit for comparing four sky models at 166 MHz with a bandwidth of 100 kHz. The HERA data agree with the GLEAM catalogs to < 10%. After subtracting the GLEAM point sources, the HERA data discriminate between the different continuum sky models, providing most support for the model of Byrne et al. We report the computation cost for mapping the HERA Phase I data and project the computation for the HERA 320-antenna data; both are feasible with a modern server. The algorithm is broadly applicable to other interferometers and is valid for wide-field and noncoplanar arrays.

Improved Constraints on the 21 cm EoR Power Spectrum and the X-Ray Heating of the IGM with HERA Phase I Observations

“…Power spectrum estimation: We compute power spectra using the delay approximation, in which we substitute a Fourier transform along the frequency axis of a visibility ( i.e., a delay transform) for a line-of-sight Fourier transform (Parsons et al 2012a). This strategy avoids mapmaking entirely (Dillon et al 2013(Dillon et al , 2015bXu et al 2022). We thus approximate τ and u (the magnitude of the baseline in units of wavelengths) as mapping linearly to line-of-sight Fourier modes, k ∥ , and transverse Fourier modes, k ⊥ , respectively.…”