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Quantifying the non-Gaussianity in the EoR 21-cm signal through bispectrum
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Number of Authors: 62018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 476, no 3, p. 4007-4024Article in journal (Refereed) Published
Abstract [en]

The epoch of reionization (EoR) 21-cm signal is expected to be highly non-Gaussian in nature and this non-Gaussianity is also expected to evolve with the progressing state of reionization. Therefore the signal will be correlated between different Fourier modes (k). The power spectrum will not be able capture this correlation in the signal. We use a higher order estimator - the bispectrum - to quantify this evolving non-Gaussianity. We study the bispectrum using an ensemble of simulated 21-cm signal and with a large variety of k triangles. We observe two competing sources driving the non-Gaussianity in the signal: fluctuations in the neutral fraction (X-HT) field and fluctuations in the matter density field. We find that the non-Gaussian contribution from these two sources varies, depending on the stage of reionization and on which k modes are being studied. We show that the sign of the bispectrum works as a unique marker to identify which among these two components is driving the non-Gaussianity. We propose that the sign change in the bispectrum, when plotted as a function of triangle configuration cos 0 and at a certain stage of the EoR can be used as a confirmative test for the detection of the 21-cm signal. We also propose a new consolidated way to visualize the signal evolution (with evolving (x) over bar (HT) or redshift), through the trajectories of the signal in a power spectrum and equilateral bispectrum i.e. P(k) - B(k, k, k) space.

Place, publisher, year, edition, pages
2018. Vol. 476, no 3, p. 4007-4024
Keywords [en]
methods: numerical, dark ages, reionization, first stars
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-156640DOI: 10.1093/mnras/sty535ISI: 000430944100077OAI: oai:DiVA.org:su-156640DiVA, id: diva2:1215379
Available from: 2018-06-08 Created: 2018-06-08 Last updated: 2018-06-08Bibliographically approved

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Mellema, Garrelt
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Department of AstronomyThe Oskar Klein Centre for Cosmo Particle Physics (OKC)
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