Imaging the Southern Sky at 159MHz using Spherical Harmonics with the Engineering Development Array 2

Abstract

One of the major priorities of international radio astronomy is to study the early universe through the detection of the 21 cm HI line from the epoch of reionisation (EoR). Due to the weak nature of the 21 cm signal, an important part in the detection of the EoR is removing contaminating foregrounds from our observations as they are multiple orders of magnitude brighter. In order to achieve this, sky maps spanning a wide range of frequencies and angular scales are required for calibration and foreground subtraction. Complementing the existing low-frequency sky maps, we have constructed a Southern Sky map through spherical harmonic transit interferometry utilising the engineering development array 2 (EDA2), a square kilometre array (SKA) low-frequency array prototype system. We use the m-mode formalism to create an all-sky map at 159MHz with an angular resolution of 3 degrees, with data from the (EDA2) providing information over +60 degrees to -90 degrees in declination. We also introduce a new method for visualising and quantifying how the baseline distribution of an interferometer maps to the spherical harmonics, and discuss how prior information can be used to constrain spherical harmonic components that the interferometer is not sensitive to.

29 pages, 35 figures, accepted in PASA (11-01-2022)

References in corpus (10)

• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• Observational constraints on Cosmic Reionization
• All-sky Galactic radiation at 45 MHz and spectral index between 45 and 408 MHz
• Characterisation of the ionosphere above the Murchison Radio Observatory using the Murchison Widefield Array
• Improved Measurement of the Spectral Index of the Diffuse Radio Background Between 90 and 190 MHz
• SARAS measurement of the Radio Background at long wavelengths
• Fine Structures and Overlying Loops of Confined Solar Flares
• Absolute Calibration of Diffuse Radio Surveys at 45 and 150 MHz
• The All-Sky SignAl Short-Spacing INterferometer (ASSASSIN) I: Global sky measurements with the Engineering Development Array-2
• Imaging on a Sphere with Interferometers: the Spherical Wave Harmonic Transform