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 (Wayth et al. 2015) 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. (2021). 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 non-coplanar
arrays.