Improved limits on the 21cm signal at z=6.5-7.0 with the MWA using Gaussian information

TL;DR

This paper presents improved upper limits on the 21cm signal during the Epoch of Reionization at redshifts 6.5-7.0 by analyzing Gaussian components of interferometric data from the MWA, accounting for foreground contamination.

Contribution

It introduces a method to separate Gaussian from non-Gaussian signals in 21cm data, leading to tighter constraints on the EoR power spectrum.

Findings

Improved 2-sigma upper limits on 21cm power spectrum at z=6.5-7.0.

Foreground contamination causes non-Gaussianity in measurements.

Gaussian component extraction enhances sensitivity to the 21cm signal.

Abstract

We explore the properties of interferometric data from high-redshift 21~cm measurements using the Murchison Widefield Array. These data contain redshifted 21~cm signal, contamination from continuum foreground sources, and radiometric noise. The 21~cm signal from the Epoch of Reionization is expected to be highly-Gaussian, which motivates the use of the power spectrum as an effective statistical tool for extracting astrophysical information. We find that foreground contamination introduces non-Gaussianity into the distribution of measurements, and then use this information to separate Gaussian from non-Gaussian signal. We present improved upper limits on the 21cm EoR power spectrum from the MWA using a Gaussian component of the data, based on the existing analysis from Nunhokee et al (2025). This is extracted as the best-fitting Gaussian to the measured data. Our best 2 sigma (thermal+sample variance) limit for 268 hours of data improves from (30.2~mK)^2 to (23.0~mK)^2 at z=6.5 for the EW polarisation, and from (39.2~mK)^2 to (21.7~mK)^2 = 470~mK^2 in NS. The best limits at z=6.8 (z=7.0) improve to P < (25.9~mK)^2 (P < (32.0~mK)^2), and k = 0.18h/Mpc (k = 0.21h/Mpc). Results are compared with realistic simulations, which indicate that leakage from foreground contamination is a source of the non-Gaussian behaviour.