On Measuring the 21 cm Global Spectrum of the Cosmic Dawn with an Interferometer Array

Abstract

Abstract We theoretically investigate the recovery of the global spectrum (monopole) from visibilities (cross-correlation only) measured by an interferometer array and the feasibility of extracting the 21 cm signal of the cosmic dawn. In our approach, the global spectrum is obtained by solving the monopole and higher-order components simultaneously from visibilities measured with up to thousands of baselines. Using this algorithm, the monopole of both the foreground and the 21 cm signal can be correctly recovered in a broad range of conditions. We find that a 3D baseline distribution can have much better performance than a 2D (planar) baseline distribution, particularly when there is a lack of shorter baselines. We simulate for ground-based 2D and 3D array configurations, and a cross-shaped space array located at the Sun–Earth L2 point that can form 3D baselines through orbital precession. In all simulations we obtain a good recovered global spectrum, and successfully extract the 21 cm signal from it, with a reasonable number of antennas and observation time.