2018/07/31 by J. Colin Hill
Physics and Astronomy · #Anisotropy #Astrophysics #Bispectrum #Black-body radiation #Cosmic background radiation #Cosmic microwave background #Cosmology and Gravitation Theories #Galaxies: Formation, Evolution, Phenomena #Non-Gaussianity #Physics #Planck #Quantum mechanics #Radiation #Radio Astronomy Observations and Technology #Spectral density #Statistics #astro-ph.CO #hep-ph #hep-th
paper · pdf · doi:10.1103/physrevd.98.083542
published as Phys. Rev. D 98, 083542 (2018) · 18 pages, 10 figures, abstract slightly abridged, comments welcome; v2: 26 pages, 22 figures, results unchanged, added new results for equilateral and orthogonal NG; v3: matches published version
openalex created_date 2018/08/03 · openalex publication_date 2018/10/31 · arxiv created 2018/11/02 · arxiv updated 2018/11/06 · openalex updated_date 2026/08/05
The cosmic microwave background temperature bispectrum is currently the most precise tool for constraining non-Gaussianity (NG) in the primordial curvature perturbations. The Planck temperature data tightly constrain the amplitude of local-type NG: fNLloc=2.5\ifmmode±\else\textpm\fi5.7. In this paper, we compute previously neglected foreground biases in temperature-based fNLloc measurements. We consider signals from the integrated Sachs-Wolfe (ISW) effect, gravitational lensing, the thermal and kinematic Sunyaev-Zel'dovich effects, and the cosmic infrared background. In standard analyses, a significant foreground bias arising from the ISW-lensing bispectrum is subtracted from the fNLloc measurement. However, a number of other terms sourced by the ISW, lensing, thermal and kinematic Sunyaev-Zel'dovich effects, and cosmic infrared background fields are also present in the temperature bispectrum. We compute the dominant biases on fNLloc arising from these signals, focusing on ``squeezed'' bispectrum shapes. Most of the biases are nonblackbody in nature, and are thus reduced by multifrequency component separation methods; however, recent analyses have found that extragalactic foregrounds are present at non-negligible levels in the Planck component-separated maps. Moreover, the Planck FFP8 simulations do not include the correlations amongst components that are responsible for these biases. We compute the biases for individual Planck frequencies, finding that some are comparable to the statistical error bar on fNLloc, even for the main cosmic microwave background channels (100, 143, and 217 GHz). For future experiments, they can greatly exceed the statistical error bar (considering temperature data only). Alternatively, the foreground contributions can be marginalized over, but without strong priors this leads to a non-negligible increase in the error bar on fNLloc. A full assessment for Planck and other experiments will require calculations in tandem with component separation, ideally using simulations. We also compute these biases for equilateral and orthogonal NG, finding large effects for the latter. Similar calculations must be performed for trispectrum NG. We conclude that the search for primordial NG using Planck data may not yet be over.