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Improving CMB non-Gaussianity estimators using tracers of local structure

James M. G. Mead1,*, Antony Lewis2,†, and Lindsay King1

  • 1Institute of Astronomy and Kavli Institute for Cosmology Cambridge, University of Cambridge, Madingley Road, Cambridge CB3 OHA, United Kingdom
  • 2Department of Physics & Astronomy, University of Sussex, Brighton BN1 9QH, United Kingdom

  • *jmead@ast.cam.ac.uk
  • †http://cosmologist.info
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Phys. Rev. D 83, 023507 – Published 10 January, 2011

DOI: https://doi.org/10.1103/PhysRevD.83.023507

Abstract

Local non-Gaussianity causes correlations between large-scale perturbation modes and the small-scale power. The large-scale CMB signal has contributions from the integrated Sachs-Wolfe (ISW) effect, which does not correlate with the small-scale power. If this ISW contribution can be removed, the sensitivity to local non-Gaussianity is improved. Gravitational lensing and galaxy counts can be used to trace the ISW contribution; in particular, we show that the CMB lensing potential is highly correlated with the ISW signal. We construct a nearly optimal estimator for the local non-Gaussianity parameter fNL and investigate to what extent we can use this to decrease the variance on fNL. We show that the variance can be decreased by up to 20% at Planck sensitivity using galaxy counts. CMB lensing is a good bias-independent ISW tracer for future more sensitive observations, though the fractional decrease in variance is small if good polarization data are also available.

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Phys. Rev. D 83, 023507– Published 10 January, 2011
  • Received 10 September 2010

© 2011 The American Physical Society

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