21-cm Epoch of reionisation power spectrum with closure phase using the Murchison Widefield Array
The radio interferometric closure phases can be a valuable tool for studying cosmological HI from the early Universe. Closure phases have the advantage of being immune to element-based gains and associated calibration errors. Thus, calibration and errors therein, which are often sources of systemati...
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Published in | Publications of the Astronomical Society of Australia Vol. 41 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
New York, USA
Cambridge University Press
18.10.2024
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Subjects | |
Online Access | Get full text |
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Summary: | The radio interferometric closure phases can be a valuable tool for studying cosmological HI from the early Universe. Closure phases have the advantage of being immune to element-based gains and associated calibration errors. Thus, calibration and errors therein, which are often sources of systematics limiting standard visibility-based approaches, can be avoided altogether in closure phase analysis. In this work, we present the first results of the closure phase power spectrum of HI 21-cm fluctuations using the Murchison Widefield Array (MWA), with
$\sim12$
h of MWA phase II observations centred around redshift,
$z\approx 6.79$
, during the Epoch of Reionisation. On analysing three redundant classes of baselines – 14, 24, and 28 m equilateral triads, our estimates of the
$2\sigma$
(95% confidence interval) 21-cm power spectra are
$\lesssim(184)^2 pseudo\,\mathrm{mK}^2$
at
${k}_{||} = 0.36 pseudo\ h \mathrm{Mpc}^{-1}$
in the EoR1 field for the 14 m baseline triads, and
$\lesssim(188)^2 pseudo\,\mathrm{mK}^2$
at
$k_{||} = 0.18 \,pseudo\ h \mathrm{Mpc}^{-1}$
in the EoR0 field for the 24 m baseline triads. The ‘pseudo’ units denote that the length scale and brightness temperature should be interpreted as close approximations. Our best estimates are still 3-4 orders high compared to the fiducial 21-cm power spectrum; however, our approach provides promising estimates of the power spectra even with a small amount of data. These data-limited estimates can be further improved if more datasets are included into the analysis. The evidence for excess noise has a possible origin in baseline-dependent systematics in the MWA data that will require careful baseline-based strategies to mitigate, even in standard visibility-based approaches. |
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ISSN: | 1323-3580 1448-6083 |
DOI: | 10.1017/pasa.2024.81 |