Sky reconstruction for the Tianlai cylinder array

TL;DR

This paper develops a spherical harmonic-based sky map reconstruction method for the Tianlai cylinder array, addressing issues like grating lobes and demonstrating improved imaging with irregular feed spacing.

Contribution

It introduces a sky reconstruction technique applicable to cylindrical arrays, including methods to mitigate grating lobes through irregular feed spacing.

Findings

Regular feed spacing causes spurious images due to grating lobes.

Irregular feed spacing reduces grating lobes and improves map quality.

Reconstructed maps show effective noise and beam characteristics.

Abstract

In this paper, we apply our sky map reconstruction method for transit type interferometers to the Tianlai cylinder array. The method is based on the spherical harmonic decomposition, and can be applied to cylindrical array as well as dish arrays and we can compute the instrument response, synthesised beam, transfer function and the noise power spectrum. We consider cylinder arrays with feed spacing larger than half wavelength, and as expected, we find that the arrays with regular spacing have grating lobes which produce spurious images in the reconstructed maps. We show that this problem can be overcome, using arrays with different feed spacing on each cylinder. We present the reconstructed maps, and study the performance in terms of noise power spectrum, transfer function and beams for both regular and irregular feed spacing configurations.