The scale of the problem: Recovering images of reionization with Generalized Morphological Component Analysis

Emma Chapman*, Filipe B. Abdalla, J. Bobin, J-L Starck, Geraint Harker, Vibor Jelic, Panagiotis Labropoulos, Saleem Zaroubi, Michiel A. Brentjens, A. G. de Bruyn, L.V.E. Koopmans

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Abstract

The accurate and precise removal of 21-cm foregrounds from Epoch of Reionization (EoR) redshifted 21-cm emission data is essential if we are to gain insight into an unexplored cosmological era. We apply a non-parametric technique, Generalized Morphological Component Analysis (GMCA), to simulated Low Frequency Array (LOFAR)-EoR data and show that it has the ability to clean the foregrounds with high accuracy. We recover the 21-cm 1D, 2D and 3D power spectra with high accuracy across an impressive range of frequencies and scales. We show that GMCA preserves the 21-cm phase information, especially when the smallest spatial scale data is discarded. While it has been shown that LOFAR-EoR image recovery is theoretically possible using image smoothing, we add that wavelet decomposition is an efficient way of recovering 21-cm signal maps to the same or greater order of accuracy with more flexibility. By comparing the GMCA output residual maps (equal to the noise, 21-cm signal and any foreground fitting errors) with the 21-cm maps at one frequency and discarding the smaller wavelet scale information, we find a correlation coefficient of 0.689, compared to 0.588 for the equivalently smoothed image. Considering only the pixels in a central patch covering 50 per cent of the total map area, these coefficients improve to 0.905 and 0.605, respectively, and we conclude that wavelet decomposition is a significantly more powerful method to denoise reconstructed 21-cm maps than smoothing.

Original languageEnglish
Pages (from-to)165-176
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Volume429
Issue number1
DOIs
Publication statusPublished - 11-Feb-2013

Keywords

  • methods: statistical
  • cosmology: theory
  • dark ages, reionization, first stars
  • diffuse radiation
  • BLIND SOURCE SEPARATION
  • 21 CENTIMETER FLUCTUATIONS
  • FOREGROUND REMOVAL
  • HIGH-REDSHIFT
  • INTERGALACTIC MEDIUM
  • NEUTRAL HYDROGEN
  • 21-CM EPOCH
  • TOMOGRAPHY
  • LOFAR
  • SIMULATIONS

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