The 21-cm bispectrum as a probe of non-Gaussianities due to X-ray heating

Watkinson, Catherine A.; Giri, Sambit K.; Ross, Hannah E; Dixon, Keri L.; Iliev, Ilian T.; Mellema, Garrelt; Pritchard, Jonathan R.

doi:10.1093/mnras/sty2740

Cited by 76 publications

(78 citation statements)

References 74 publications

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“…Ref. [52] indeed confirmed that there is a clear effect present in the measurements of the bispectrum. How about observational prospects of the response functions?…”

Section: Summary and Discussionmentioning

confidence: 66%

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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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“…Ref. [52] indeed confirmed that there is a clear effect present in the measurements of the bispectrum. How about observational prospects of the response functions?…”

Section: Summary and Discussionmentioning

confidence: 66%

“…Ref. [52] have carried out a theoretical study of detectability of the bispectrum in SKA-Low observations in the presence of telescope noise. They find that for 1000-hour integration time the bispectrum from the equilateral triangle configuration will be detectable.…”

Section: Summary and Discussionmentioning

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.

Self Cite

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“…This result further motivates the use of alternative analysis techniques to interpret the signal from the CD to probe for rare X-ray sources. The bispectra of the 21-cm signals from all the X-ray simulations presented here have been extensively studied in Watkinson et al (2019).…”

Section: Discussionmentioning

confidence: 99%

Evaluating the QSO contribution to the 21-cm signal from the Cosmic Dawn

Ross

Dixon

Ghara

et al. 2019

Monthly Notices of the Royal Astronomical Society

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The upcoming radio interferometer Square Kilometre Array (SKA) is expected to directly detect the redshifted 21-cm signal from the neutral hydrogen present during the Cosmic Dawn. Temperature fluctuations from X-ray heating of the neutral intergalactic medium can dominate the fluctuations in the 21-cm signal from this time. This heating depends on the abundance, clustering, and properties of the X-ray sources present, which remain highly uncertain. We present a suite of three new large-volume, 349 Mpc a side, fully numerical radiative transfer simulations including QSO-like sources, extending the work previously presented in Ross et al. (2017). The results show that our QSOs have a modest contribution to the heating budget, yet significantly impact the 21-cm signal. Initially, the power spectrum is boosted on large scales by heating from the biased QSO-like sources, before decreasing on all scales. Fluctuations from images of the 21-cm signal with resolutions corresponding to SKA1-Low at the appropriate redshifts are well above the expected noise for deep integrations, indicating that imaging could be feasible for all the X-ray source models considered. The most notable contribution of the QSOs is a dramatic increase in non-Gaussianity of the signal, as measured by the skewness and kurtosis of the 21-cm probability distribution functions. However, in the case of late Lyman-α saturation, this non-Gaussianity could be dramatically decreased particularly when heating occurs earlier. We conclude that increased non-Gaussianity is a promising signature of rare X-ray sources at this time, provided that Lyman-α saturation occurs before heating dominates the 21-cm signal.

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“…This is compensated for by having a wider range of baselines, meaning a fuller interferometric U-V coverage. Despite this SKA does not achieve tighter posterior contours on parameters, when considering the power spectrum -this might not remain the case when considering higher order statistics such as the bispectrum (Watkinson et al 2019). For a direct comparison of HERA-331 and SKA's observational error on the power spectrum see Figure 4.…”

Section: Varying the Number Of Hera Dipolesmentioning

confidence: 99%

Bayesian model selection with future 21cm observations of the epoch of reionization

Binnie

Pritchard

2019

Monthly Notices of the Royal Astronomical Society

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We apply Bayesian statistics to perform model selection on different reionisation scenarios via the Multinest algorithm. Initially, we recover the results shown by 21CMMC for the parameter estimation of 21cmFAST models. We proceed to test several toy models of the Epoch of Reionisation (EoR) defined in contrasting morphology and scale. We find that LOFAR observations are unlikely to allow model selection even with long integration times. HERA would require 61 dipoles to perform the same analysis in 1080 hours, and becomes comparable to the SKA with 217 dipoles. We find the SKA requires only 324 hours of observation to conclusively distinguish between our models. Once model selection is achievable, an analysis of observational priors is performed finding that neutral fraction checks at specific redshifts add little to no inference. We show the difficulties in model selection at the level of distinguishing fiducial parameters within a model or distinguishing galaxies with a constant versus power law mass-to-light ratio. Finally, we explore the use of the Savage-Dickey density ratio to show the redundancy of the parameter R mfp within 21cmFAST.

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The 21-cm bispectrum as a probe of non-Gaussianities due to X-ray heating

Cited by 76 publications

References 74 publications

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

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

Evaluating the QSO contribution to the 21-cm signal from the Cosmic Dawn

Bayesian model selection with future 21cm observations of the epoch of reionization

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