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

Abstract

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

Hydrogen Epoch of Reionization Array (HERA) Phase II Deployment and Commissioning

“…This was subsequently confirmed experimentally by varying feed height and observing changes in autocorrelations. Kim et al (2022) found in simulation that feed positioning should be accurate to the 1 centimeter level in position and 1°in tilt to minimize foreground leakage in power spectra. This leakage is caused by calibration errors, as the feed positioning offset impacts array redundancy.…”

Direct Optimal Mapping Image Power Spectrum and its Window Functions

“…noiseless simulations. We will investigate the effects of realistic noise, radio-frequency interference, realistic errors in beam models, calibration accuracy, realistic antenna position, and beam variations (Orosz et al 2019;Aguirre et al 2022;Kim et al 2022Kim et al , 2023.…”

Impact of beam systematics on the OVRO-LWA science cases: 21-cm cosmology & Exoplanet studies.

“…In general, precisely measuring or modeling the complex beam patterns antenna elements over the entire bandwidth of operation is difficult and errors can manifest due to various factors: environmental conditions such as soil moisture and electrical properties variation, manufacturing defects, and positioning errors, mutual coupling and cross-talk between individual antennas in the interferometer [6,7]. In addition, all of these effects can vary with time.…”