POWER ASYMMETRY IN COSMIC MICROWAVE BACKGROUND FLUCTUATIONS FROM FULL SKY TO SUB-DEGREE SCALES: IS THE UNIVERSE ISOTROPIC?

By F. Hansen, A. Banday, K. G'orski, H. Eriksen, P. Lilje. 2008

182 citations recorded by the source corpus.

We repeat and extend the analysis of Eriksen et al. and Hansen et al., testing the isotropy of the cosmic microwave background fluctuations. We find that the hemispherical power asymmetry previously reported for the largest scales ℓ = 2–40 extends to much smaller scales. In fact, for the full multipole range ℓ = 2–600, significantly more power is found in the hemisphere centered at (θ = 107° ± 10°, ϕ = 226° ± 10°) in galactic co-latitude and longitude than in the opposite hemisphere, consistent with the previously detected direction of asymmetry for ℓ = 2–40. We adopt a model selection test where the direction and amplitude of asymmetry, as well as the multipole range, are free parameters. A model with an asymmetric distribution of power for ℓ = 2–600 is found to be preferred over the isotropic model at the 0.4% significance level, taking into account the additional parameters required to describe it. A similar direction of asymmetry is found independently in all six subranges of 100 multipoles between ℓ = 2–600. None of our 9800 isotropic simulated maps show a similarly consistent direction of asymmetry over such a large multipole range. No known systematic effects or foregrounds are found to be able to explain the asymmetry.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/eca4f4a68fcbd9f198a9e7ff329ef1a1415733ea

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In Astronomy and Astrophysics

1. E. Komatsu
2. A. Banday
3. David N. Spergel
4. Mark Halpern
5. C. Bennett
6. K. G'orski
7. J. Weiland
8. H. Eriksen

Citations in the corpus

• SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP ) OBSERVATIONS: ARE THERE COSMIC MICROWAVE BACKGROUND ANOMALIES? (2010, methodology): “In Hansen et al. (2009), the significance of a 2 ≤ l ≤ 600 hemispherical power asymmetry was quoted as 99.6%.”
• POWER ASYMMETRY IN WMAP AND PLANCK TEMPERATURE SKY MAPS AS MEASURED BY A LOCAL VARIANCE ESTIMATOR (2014, methodology): “…and is with current data sets generally found to be statistically significant at the 3σ–3.5σ level depending on the algorithm and angular scales under considerations (Park 2004; Eriksen et al. 2007; Hansen et al. 2009; Hoftuft et al. 2009; Axelsson et al. 2013; Planck Collaboration 2013d).”