Redundant Array Configurations for 21 cm Cosmology

TL;DR

This paper evaluates array configurations for 21 cm cosmology, demonstrating how modifications to dense, redundant arrays like HERA can improve imaging, calibration, and foreground mitigation for Epoch of Reionization studies.

Contribution

It introduces and compares array configurations that enhance calibration and imaging capabilities while maintaining high sensitivity for 21 cm cosmology.

Findings

Modest array modifications improve imaging and calibration.

Off-grid antennas enhance sub-aperture sampling.

Outrigger antennas increase angular resolution.

Abstract

Realizing the potential of 21 cm tomography to statistically probe the intergalactic medium before and during the Epoch of Reionization requires large telescopes and precise control of systematics. Next-generation telescopes are now being designed and built to meet these challenges, drawing lessons from first-generation experiments that showed the benefits of densely packed, highly redundant arrays--in which the same mode on the sky is sampled by many antenna pairs--for achieving high sensitivity, precise calibration, and robust foreground mitigation. In this work, we focus on the Hydrogen Epoch of Reionization Array (HERA) as an interferometer with a dense, redundant core designed following these lessons to be optimized for 21 cm cosmology. We show how modestly supplementing or modifying a compact design like HERA's can still deliver high sensitivity while enhancing strategies for calibration and foreground mitigation. In particular, we compare the imaging capability of several array configurations, both instantaneously (to address instrumental and ionospheric effects) and with rotation synthesis (for foreground removal). We also examine the effects that configuration has on calibratability using instantaneous redundancy. We find that improved imaging with sub-aperture sampling via "off-grid" antennas and increased angular resolution via far-flung "outrigger" antennas is possible with a redundantly calibratable array configuration.