Exploring one-point statistics in HERA phase I data: effects of foregrounds and systematics on measuring one-point statistics

Abstract

The epoch of reionization (EoR) marks a pivotal phase in cosmic evolution, transitioning the intergalactic medium (IGM) from mostly neutral to ionized. Studying this transition offers key insights into the formation of the first luminous sources. A primary observable from the EoR is the redshifted 21 cm line emission, originating from hyperfine splitting in ground-state neutral hydrogen. Radio interferometers, designed to detect these faint signals, are crucial for characterizing the EoR. In recent years, various radio interferometers have undertaken extensive efforts to probe the power spectrum of 21 cm fluctuations during the EoR, leading to several upper limits. These include the Giant Meter Wave Radio Telescope (GMRT; G. Paciga et al. 2013), the Murchison Widefield Array (MWA; S. J. Tingay et al. 2013; J. S. Dillon et al. 2014; A. P. Beardsley et al. 2016; N. Barry et al. 2019; C. M. Trott et al. 2020), the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER; A. R. Parsons et al. 2010; C. Cheng et al. 2018; M. Kolopanis et al. 2019), the Low Frequency Array (LOFAR; van Haarlem et al. 2013; A. H. Patil et al. 2017; F. G. Mertens et al. 2020; R. Ghara et al. 2025), and the Hydrogen Epoch of Reionization Array (HERA; J. S. Dillon & A. R. Parsons 2016; D. R. DeBoer et al. 2017; L. M. Berkhout et al. 2024). More recently, The HERA Collaboration et al. (2022a, hereafter H22a) and The HERA Collaboration et al. (2023, hereafter H23) reported upper limits on the 21 cm power spectrum. The HERA Collaboration et al. (2022b, hereafter H22b) and H23 explored the astrophysical parameter space, using these limits to constrain IGM X-ray heating and disfavor inefficient heating by z ∼ 8.