Limits on the 21 cm power spectrum at z=6.5-7.0 from MWA observations

TL;DR

This paper reports the deepest upper limits on the 21 cm power spectrum during the Epoch of Reionization from MWA data, indicating evidence of a heated intergalactic medium at redshifts 6.5 to 7.0.

Contribution

It introduces improved data analysis techniques and provides the first evidence of a heated IGM at these redshifts using MWA observations.

Findings

Lowest power spectrum limits achieved by MWA to date.

Evidence of heated intergalactic medium at z=6.5-7.0.

Power spectrum measurements at specific k-values and redshifts.

Abstract

This paper presents the spherically-averaged 21 cm power spectrum derived from Epoch of Reionization (EoR) observations conducted with the Murchison Widefield Array (MWA). The analysis uses EoR0-field data, centered at (RA$=0h$, DEC$=-27^{\circ}$), collected between 2013 and 2023. Building on the improved methodology described in Trott et al. 2020, we incorporate additional data quality control techniques introduced in Nunhokee et al. 2024. We report the lowest power level limits on the EoR power spectrum at redshifts $z=6.5$, $z=6.8$, and $z=7.0$. These power levels, measured in the East-West polarization, are $(30.2)^2$ mK$^2$ at $k=0.18\, h$ Mpc$^{-1}$, $(31.2)^2$ mK$^2$ at $k=0.18\, h$ Mpc$^{-1}$ and $(39.1)^2$ mK$^2$ at $k=0.21\, h$ Mpc$^{-1}$ respectively. The total integration time amounts to 268 hours. These results represent the deepest upper limits achieved by the MWA to date and provide the first evidence of heated intergalactic medium (IGM) at redshifts $z=6.5$ to $7.0$.