Synthesis imaging with a lunar orbit array: I. global sky map and its systematics

Abstract

Ground-based radio astronomical observation at frequencies below 30 MHz is hampered by the Ionosphere and radio frequency interference (RFI). The Discovering Sky at the Longest wavelength (DSL) mission, also known as the Hongmeng mission, employs a linear array of satellites on a circular orbit around the Moon to make interferometric observations in this band. Though vastly different from the usual ground-based arrays, the interferometric visibility data collected by such an array is linearly related to the sky map, and the reconstruction is in principle an inversion problem of linear mapping. In this paper, we investigate a number of issues in the algorithm of global map reconstruction, focusing on the impact of sub-pixel noise induced by the finite pixelization of the sky, and errors due to regularization. We find that in the reconstruction process, if one builds up the beam matrix, which relates the sky pixels to the visibilities, by naively evaluating its elements at each of the pixel centers, then the sub-pixel noise can give rise to a significant aliasing effect. However, this effect can be effectively mitigated by a simple pixel-averaging method. Based on evaluation of the image quality using the correlation coefficient between the input and reconstructed map, and the signal-to-noise ratio, we discuss the selection strategy of the regularization parameter, and show that the sky can be well reconstructed with a reasonable choice of the regularization parameter.

22 pages, 20 figures

References in corpus (23)

• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• A model of diffuse Galactic Radio Emission from 10 MHz to 100 GHz
• The non-coplanar baselines effect in radio interferometry: The W-Projection algorithm
• All-Sky Interferometry with Spherical Harmonic Transit Telescopes
• The Radio Sky at Meter Wavelengths: m-Mode Analysis Imaging with the Owens Valley Long Wavelength Array
• Discovering the Sky at the Longest wavelengths with a lunar orbit array
• Transformative Science from the Lunar Farside: Observations of the Dark Ages and Exoplanetary Systems at Low Radio Frequencies
• Source counts and confusion at 72-231 MHz in the MWA GLEAM survey
• Prospects for precision cosmology with the 21 cm signal from the dark ages
• Sky reconstruction from transit visibilities: PAON-4 and Tianlai Dish Array
• Lunar Orbit Measurement of Cosmic Dawn 21 cm Global Spectrum
• PRATUSH experiment concept and design overview
• An Ultra-long Wavelength Sky Model with Absorption Effect
• Brute-Force Mapmaking with Compact Interferometers: A MITEoR Northern Sky Map from 128 MHz to 175 MHz
• Wide field imaging for the Square Kilometre Array
• Large-scale Array for Radio Astronomy on the Farside
• Extragalactic Peaked-Spectrum Radio Sources at Low-Frequencies are Young Radio Galaxies
• An imaging algorithm for a lunar orbit interferometer array
• Antenna Design and Implementation for the Future Space Ultra-Long Wavelength Radio Telescope
• Ultra-Low-Frequency Radio Astronomy Observations from a Selenocentric Orbit: first results of the Longjiang-2 experiment
• Ground Experiments and Performance Evaluation of the Low-Frequency Radio Spectrometer Onboard the Lander of Chang'e-4 Mission
• RFSoC receiver calibration system for 21-cm global spectrum experiments from space: The CosmoCube case
• A new method of reconstructing Galactic three-dimensional structures using ultralong-wavelength radio observations