Extracting the 21 cm EoR signal using MWA drift scan data

Aug 22, 2026

The detection of redshifted hyperfine emission from neutral hydrogen (HI) is a leading probe of the Epoch of Reionization (EoR). The study analyzes 55 hours of Murchison Widefield Array (MWA) Phase II drift-scan EoR data centered at 154.24 MHz with 10.24 MHz bandwidth. Drift-scan stability is evaluated by comparing extracted power spectra against noise simulations, showing thermal-noise behavior in the cleanest data. The HI power spectrum is computed versus time in one and two dimensions, yielding best one-dimensional upper limits of Δ2≈(1000 mK)2 at k≈0.2 h Mpc−1 and k≈1 h Mpc−1. Foreground-dominated modes’ time dependence is also examined and compared to expectations.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages11

Reading Time28 min

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Abstract

Introduction

The Epoch of Reionization as a cosmology probe

Radio interferometers and global HI experiments

Challenges: foregrounds and signal separation

Related imaging and visibility-based pipelines

arXiv :2104 .03321v1 [ astro-ph .CO] 7 Apr 2021 Extracting the 21 cm EoR signal using MWA drift scan data Akash Kumar Patwa 1★ , Shiv Sethi1 , and K. S. Dwarakanath 1 1 Raman Research Institute, C. V. Raman Avenue, Sadashivanagar, Bengaluru 560080, India Accepted 2021 April 5 . Received 2021 March 3; in original form 2020 December 18 ABSTRACT The detection of redshifted hyperﬁne line of neutral hydrogen (HI) is the most promising probe of the Epoch of Reionization (EoR). We report an analysis of 55 hours of Murchison WideﬁeldArray (MWA) Phase II drift scan EoR data. The data correspond to a central frequency 􀁡0 = 154.24 MHz (􀁉 ' 8.2 for the redshifted HI hyperﬁne line) and bandwidth 􀀗 = 10.24 MHz. As one expects greater system stability in a drift scan, we test the system stability by comparing the extracted power spectra from data with noise simulations and show that the power spectra for the cleanest data behave as thermal noise. We compute the HI power spectrum as a function of time in one and two dimensions. The best upper limit on the one-dimensional power spectrum are:Δ2 (􀀺) ' (1000 mK)2 at 􀀺 ' 0.2ℎ Mpc−1and at 􀀺 ' 1ℎ Mpc−1 . The cleanest modes, which might be the most suited for obtaining the optimal signal-to-noise, correspond to 􀀺 & 1ℎ Mpc−1 . We also study the time-dependence of the foreground-dominated modes in a drift scan and compare with the expected behaviour. Key words: cosmology: observation; early Universe; dark ages, reionization, ﬁrst stars; techniques: interferometric; methods: observational; methods: data analysis 1 INTRODUCTION The probe of the end of cosmic dark age remains an outstanding issue in modern cosmology. From theoretical considerations, we expect the ﬁrst luminous objects to appear at a redshift 􀁉 ' 30. The ultraviolet and other radiation from these ﬁrst sources ionized and heated the neutral hydrogen (HI) in their neighbourhood. As the universe evolved, these ionized regions grew and merged, resulting ina fully ionized universe by 􀁉 ' 6, as suggested by the measurements of Gunn-Peterson troughs of quasars (Fan et al. 2006) . Recent Planck results on cosmic microwave background (CMB) temperature and polarization anisotropies ﬁx thereionization epoch at 􀁉 ' 7.8 (Planck Collaboration et al. 2020) . The cosmic time between the formation of the ﬁrst light sources (􀁉 ' 30, the era of cosmic dawn) and the universe becoming fully ionized (􀁉 ' 6) is generally referred to asthe Epoch of Reionization (EoR) . Many important astrophysical processes during this era, e.g. the formation of ﬁrst light sources and the evolution of ionized regions around them, can be best probed using the hyperﬁne transition of the neutral hydrogen atom. Due to the expansion of the universe, this line of rest frame frequency 􀁡 ' 1.4 GHz, redshifts to frequencies 70–200 MHz (􀁉 ' 6–20), which can be detected using meter-wave radio telescopes. Several existing and upcoming radio telescopes aim to detect both the sky-averaged and the ﬂuctuating component of redshifted HI signal, e.g. radio interferometers—Murchison Wideﬁeld Array (MWATingay et al. 2013, Bowman et al. 2013), Low Frequency Array (LOFAR van Haarlem et al. 2013), Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER Parsons et al. 2014), Hydrogen Epoch of Reionization Array (HERA DeBoer et al. ★ E-mail: [akpatwa@rri.res.in](akpatwa@rri.res.in) (AKP) 2017), and the Giant Metrewave Radio Telescope (GMRT, Paciga et al. 2013) . In addition there are multiple ongoing experiments to detect the global HI signal from this era—e.g. EDGES and SARAS (Bowman et al. 2018, Singh et al. 2018) . We focus on the ﬂuctuating component of the HI signal in this paper. There are considerable diﬃculties in the detection of this signal. Theoretical studies suggest that the strength of this signal is of the order of 10 mK at 150 MHz while the foregrounds are brighter than 100 K (for detailed review see Furlanetto et al. 2006, Morales & Wyith

FAQs

What observational signal is targeted in this study?

The work targets the redshifted hyperfine line of neutral hydrogen (HI) at 21 cm, used to probe the Epoch of Reionization (EoR).

How does the paper assess system stability with drift-scan data?

It compares extracted power spectra from the MWA drift-scan observations with noise simulations to test whether the cleanest data follow thermal-noise behavior.

What are the main results for the HI power spectrum upper limits?

The best one-dimensional upper limits are reported as Δ2≈(1000 mK)2 at k≈0.2 h Mpc−1 and at k≈1 h Mpc−1, with cleanest modes occurring around k≳1 h Mpc−1.

Aug 22, 2026

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