Quantifying the non-Gaussianity in the EoR 21-cm signal through bispectrum

Majumdar, Suman; Pritchard, Jonathan R.; Mondal, Rajesh; Watkinson, Catherine A.; Bharadwaj, Somnath; Mellema, Garrelt

doi:10.1093/mnras/sty535

Cited by 128 publications

(160 citation statements)

References 106 publications

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“…There is no fourth-moment (kurtosis) present. (More recent analysis by Majumdar et al 2018, shows similar results.) To study the observed visibility distributions, we can perform moments analysis directly on the KDE outputs 1 .…”

Section: Moments Analysissupporting

confidence: 64%

Robust statistics towards detection of the 21 cm signal from the Epoch of Reionization

Trott

Murray

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We explore methods for robust estimation of the 21 cm signal from the Epoch of Reionisation (EoR). A Kernel Density Estimator (KDE) is introduced for measuring the spatial temperature fluctuation power spectrum from the EoR. The KDE estimates the underlying probability distribution function of fluctuations as a function of spatial scale, and contains different systematic biases and errors to the typical approach to estimating the fluctuation power spectrum. Extraction of histograms of visibilities allows moments analysis to be used to discriminate foregrounds from 21 cm signal and thermal noise. We use the information available in the histograms, along with the statistical dis-similarity of foregrounds from two independent observing fields, to robustly separate foregrounds from cosmological signal, while making no assumptions about the Gaussianity of the signal. Using two independent observing fields to robustly discriminate signal from foregrounds is crucial for the analysis presented in this paper. We apply the techniques to 13 hours of Murchison Widefield Array (MWA) EoR data over two observing fields. We compare the output to that obtained with a comparative power spectrum estimation method, and demonstrate the reduced foreground contamination using this approach. Using the second moment obtained directly from the KDE distribution functions yields a factor of 2-3 improvement in power for k < 0.3h Mpc −1 compared with a matched delay space power estimator, while weighting data by additional statistics does not offer significant improvement beyond that available for thermal noise-only weights.

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Section: Moments Analysissupporting

confidence: 64%

Robust statistics towards detection of the 21 cm signal from the Epoch of Reionization

Trott

Murray

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…When applied to the 21-cm signal, eq. (2.9) has the key virtue that it contains more information than the power spectrum, but is simpler to estimate compared to the conventional bispectrum estimators [11,14,15].…”

Section: Position-dependent Power Spectrum As a Probe Of The Squeezedmentioning

confidence: 99%

Position-dependent power spectra of the 21-cm signal from the epoch of reionization

Giri

D’Aloisio

Mellema

et al. 2019

J. Cosmol. Astropart. Phys.

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The 21-cm signal from the epoch of reionization is non-Gaussian. Current radio telescopes are focused on detecting the 21-cm power spectrum, but in the future the Square Kilometre Array is anticipated to provide a first measurement of the bispectrum. Previous studies have shown that the position-dependent power spectrum is a simple and efficient way to probe the squeezed-limit bispectrum. In this approach, the survey is divided into subvolumes and the correlation between the local power spectrum and the corresponding mean density of the subvolume is computed. This correlation is equivalent to an integral of the bispectrum in the squeezed limit, but is much simpler to implement than the usual bispectrum estimators. It also has a clear physical interpretation: it describes how the smallscale power spectrum of tracers such as galaxies and the 21-cm signal respond to a large-scale environment. Reionization naturally couples large and small scales as ionizing radiation produced by galactic sources can travel up to tens of Megaparsecs through the intergalactic medium during this process. Here we apply the position-dependent power spectrum approach to fluctuations in the 21-cm background from reionization. We show that this statistic has a distinctive evolution in time that can be understood with a simple analytic model. We also show that the statistic can easily distinguish between simple "inside-out" and "outside-in" models of reionization. The position-dependent power spectrum is thus a promising method to validate the reionization signal and to extract higher-order information on this process.

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“…Note that the oscillations on the left side of the peak are due to the sharp edges of the bubbles: when symmetrical Gaussian distributions are used instead of binary bubbles, or once the field is smoothed by a given angular resolution, they vanish. We refer the interested reader to Watkinson et al (2017) and Majumdar et al (2018), where the authors discuss the various problems induced by solid spheres in the bispectrum. Finally, a comparison of numerical results with an analytical derivation of the TCF for a similar toy model can eb found in Appendix A.…”

Section: Application To Simulated Ionisation Fieldsmentioning

confidence: 99%

Studying the morphology of reionization with the triangle correlation function of phases

Gorce

Pritchard

2019

Monthly Notices of the Royal Astronomical Society

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We present a new statistical tool, called the triangle correlation function (TCF), inspired by the earlier work of Obreschkow et al. (2013). It is derived from the 3-point correlation function and aims to probe the characteristic scale of ionised regions during the Epoch of Reionisation from 21cm interferometric observations. Unlike most works, which focus on power spectrum, i.e. amplitude information, our statistic is based on the information we can extract from the phases of the Fourier transform of the ionisation field. In this perspective, it may benefit from the well-known interferometric concept of closure phases. We find that this statistical estimator performs very well on simple ionisation fields. For example, with well-defined fully ionised disks, there is a peaking scale, which we can relate to the radius of the ionised bubbles. We also explore the robustness of the TCF when observational effects such as angular resolution and noise are considered. We also get interesting results on fields generated by more elaborate simulations such as 21CMFAST. Although the variety of sources and ionised morphologies in the early stages of the process make its interpretation more challenging, the nature of the signal can tell us about the stage of reionisation. Finally, and in contrast to other bubble size distribution algorithms, we show that the TCF can resolve two different characteristic scales in a given map.

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Quantifying the non-Gaussianity in the EoR 21-cm signal through bispectrum

Cited by 128 publications

References 106 publications

Robust statistics towards detection of the 21 cm signal from the Epoch of Reionization

Robust statistics towards detection of the 21 cm signal from the Epoch of Reionization

Position-dependent power spectra of the 21-cm signal from the epoch of reionization

Studying the morphology of reionization with the triangle correlation function of phases

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