Deconvolving the wedge: maximum-likelihood power spectra via spherical-wave visibility modelling

Ghosh, A., Mertens, F. G. & Koopmans, L. V. E., Mar-2018, In : Monthly Notices of the Royal Astronomical Society. 474, 4, p. 4552-4563 12 p.

Research output: Contribution to journalArticleAcademicpeer-review

Direct detection of the Epoch of Reionization (EoR) via the red-shifted 21-cm line will have unprecedented implications on the study of structure formation in the infant Universe. To fulfil this promise, current and future 21-cm experiments need to detect this weak EoR signal in the presence of foregrounds that are several orders of magnitude larger. This requires extreme noise control and improved wide-field high dynamic-range imaging techniques. We propose a new imaging method based on a maximum likelihood framework which solves for the interferometric equation directly on the sphere, or equivalently in the uvw-domain. The method uses the one-to-one relation between spherical waves and spherical harmonics (SpH). It consistently handles signals from the entire sky, and does not require a w-term correction. The SpH coefficients represent the sky-brightness distribution and the visibilities in the uvw-domain, and provide a direct estimate of the spatial power spectrum. Using these spectrally smooth SpH coefficients, bright foregrounds can be removed from the signal, including their side-lobe noise, which is one of the limiting factors in high dynamics-range wide-field imaging. Chromatic effects causing the so-called 'wedge' are effectively eliminated (i.e. deconvolved) in the cylindrical (k(perpendicular to), k(parallel to)) power spectrum, compared to a power spectrum computed directly from the images of the foreground visibilities where the wedge is clearly present. We illustrate our method using simulated Low-Frequency Array observations, finding an excellent reconstruction of the input EoR signal with minimal bias.

Original languageEnglish
Pages (from-to)4552-4563
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - Mar-2018


  • methods: data analysis, techniques: interferometric, diffuse radiation, large-scale structure of Universe, cosmology: observations, QUASAR ULAS J1120+0641, 21 CM RADIATION, FOREGROUND REMOVAL, REDSHIFTED 21-CM, INTERFEROMETRIC OBSERVATIONS, INTERGALACTIC MEDIUM, COSMIC REIONIZATION, SPIN TEMPERATURE, NEUTRAL GAS, EPOCH

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