INCREASING EVIDENCE FOR HEMISPHERICAL POWER ASYMMETRY IN THE FIVE-YEAR WMAP DATA

By J. Hoftuft, H. Eriksen, A. Banday, K. G'orski, F. Hansen, P. Lilje. 2009

248 citations recorded by the source corpus.

Motivated by the recent results of Hansen et al. concerning a noticeable hemispherical power asymmetry in the Wilkinson Microwave Anisotropy Probe (WMAP) data on small angular scales, we revisit the dipole-modulated signal model introduced by Gordon et al.. This model assumes that the true cosmic microwave background signal consists of a Gaussian isotropic random field modulated by a dipole, and is characterized by an overall modulation amplitude, A, and a preferred direction, . Previous analyses of this model have been restricted to very low resolution (i.e., 3.°6 pixels, a smoothing scale of 9° FWHM, and ℓ ≲ 40) due to computational cost. In this paper, we double the angular resolution (i.e., 1.°8 pixels and 4.°5 FWHM smoothing scale), and compute the full corresponding posterior distribution for the five-year WMAP data. The results from our analysis are the following: the best-fit modulation amplitude for ℓ ⩽ 64 and the ILC data with the WMAP KQ85 sky cut is A = 0.072 ± 0.022, nonzero at 3.3σ, and the preferred direction points toward Galactic coordinates (l, b) = (224°, − 22°) ± 24°. The corresponding results for ℓ ≲ 40 from earlier analyses were A = 0.11 ± 0.04 and (l, b) = (225°, − 27°). The statistical significance of a nonzero amplitude thus increases from 2.8σ to 3.3σ when increasing ℓmax from 40 to 64, and all results are consistent to within 1σ. Similarly, the Bayesian log-evidence difference with respect to the isotropic model increases from Δln E = 1.8 to Δln E = 2.6, ranking as “strong evidence” on the Jeffreys' scale. The raw best-fit log-likelihood difference increases from to . Similar, and often slightly stronger, results are found for other data combinations. Thus, we find that the evidence for a dipole power distribution in the WMAP data increases with ℓ in the five-year WMAP data set, in agreement with the reports of Hansen et al.

Subfields: Applied Mathematics, Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/e79f1931f26a6f968740246c023e147df73054f1

How researchers see this paper

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In Applied Mathematics

1. Antonino Del Popolo
2. Morgan Le Delliou

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

• Small scale problems of the $\Lambda$CDM model: a short review (2016, methodology): “s. This is shown in Fig.14. Both the left, and right panels display RCs with Vmax < 24km/s while simulations have much larger values. Rotation curves obtained from NFW-shaped subhaloes with Vmax = (12,18,24,40)km/s, with a 1 s scatter, taken from Aquarius simulations, present the simulation side ”
• POWER ASYMMETRY IN WMAP AND PLANCK TEMPERATURE SKY MAPS AS MEASURED BY A LOCAL VARIANCE ESTIMATOR (2014, background): “However, given that the 9 year WMAP sky maps are virtually indistinguishable from the 5 year sky maps on angular scales larger than 5◦ relative to cosmic variance, we expect the dipole modulation results to be very close to those reported by Hoftuft et al. (2009) for the 5 year WMAP data.”
• SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP ) OBSERVATIONS: ARE THERE COSMIC MICROWAVE BACKGROUND ANOMALIES? (2010, methodology): “However, analyses that use optimal estimators (as we do in our analysis below) have all studied the dipolar modulation (e.g., Hoftuft et al. 2009; Hanson & Lewis 2009).”