The Impact of Beam Variations on Power Spectrum Estimation for 21-cm Cosmology I: Simulations of Foreground Contamination for HERA

TL;DR

This paper simulates how feed-induced beam perturbations in HERA affect foreground contamination in power spectrum measurements, highlighting the need for mitigation strategies to improve Epoch of Reionization signal detection.

Contribution

It provides a detailed simulation and analysis of primary beam perturbations caused by feed motions and their impact on foreground leakage in HERA's power spectrum measurements.

Findings

Vertical feed motions mainly cause leakage from point sources near zenith.

Horizontal and tilting motions lead to leakage from diffuse sources near the horizon.

Different feed motions affect foreground contamination differently depending on source type.

Abstract

Detecting cosmological signals from the Epoch of Reionization (EoR) requires high-precision calibration to isolate the cosmological signals from foreground emission. In radio interferometery, perturbed primary beams of antenna elements can disrupt the precise calibration, which results in contaminating the foreground-free region, or the EoR window, in the cylindrically averaged power spectrum. For Hydrogen Epoch of Reionization Array (HERA), we simulate and characterize the perturbed primary beams induced by feed motions such as axial, lateral, and tilting motions, above the 14-meter dish. To understand the effect of the perturbed beams, visibility measurements are modeled with two different foreground components, point sources and diffuse sources, and we find different feed motions present a different reaction to each type of sky source. HERA's redundant-baseline calibration in the presence of non-redundant antenna beams due to feed motions introduces chromatic errors in gain solutions, which produces foreground power leakage into the EoR window. The observed leakage from vertical feed motions comes predominately from point sources around zenith. Furthermore, the observed leakage from horizontal and tilting feed motion comes predominately from the diffuse components near the horizon. Mitigation of chromatic gain errors will be necessary for robust detection of the EoR signals with minimal foreground bias, and this will be discussed in the subsequent paper.