2020/10/31 by Dominic Anstey, Eloy de Lera Acedo, Will Handley · 2 citations
Engineering · Physics and Astronomy · #Antenna (radio) #Antenna Design and Optimization #Astrophysics #Chromatic scale #Chromaticity #Computer science #Millimeter-Wave Propagation and Modeling #Optics #Physics #Radio Astronomy Observations and Technology #Remote sensing #Sky #Telecommunications #astro-ph.IM
paper · pdf · doi:10.1093/mnras/stab1765
20 pages, 18 figures
openalex publication_date 2021/06/18 · arxiv created 2021/11/11 · arxiv updated 2021/11/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
ABSTRACT The H i 21 cm absorption line is masked by bright foregrounds and systematic distortions that arise due to the chromaticity of the antenna used to make the observation coupling to the spectral inhomogeneity of these foregrounds. We demonstrate that these distortions are sufficient to conceal the 21 cm signal when the antenna is not perfectly achromatic and that simple corrections assuming a constant spatial distribution of foreground power are insufficient to overcome them. We then propose a new physics-motivated method of modelling the foregrounds of 21 cm experiments in order to fit the chromatic distortions as part of the foregrounds. This is done by generating a simulated sky model across the observing band by dividing the sky into N regions and scaling a base map assuming a distinct uniform spectral index in each region. The resulting sky map can then be convolved with a model of the antenna beam to give a model of foregrounds and chromaticity parametrized by the spectral indices of the N regions. We demonstrate that fitting this model for varying N using a Bayesian nested sampling algorithm and comparing the results using the evidence allows the 21 cm signal to be reliably detected in data of a relatively smooth conical log spiral antenna. We also test a much more chromatic conical sinuous antenna and find this model will not produce a reliable signal detection, but in a manner that is easily distinguishable from a true detection.