Increasing evidence for hemispherical power asymmetry in the five-year WMAP data

Details Increasing evidence for hemispherical power asymmetry in the five-year WMAP data Increasing evidence for hemispherical power asymmetry in the five-year WMAP data

2009-03-06

arxiv.org/abs/0903.1229v2

Astrophys.J.699:985-989,2009

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

6 pages, 2 figures; added references and minor comments. Accepted for publication in ApJ

Scientific paper

10.1088/0004-637X/699/2/985

(Abridged)Motivated by the recent results of Hansen et al. (2008) concerning a noticeable hemispherical power asymmetry in the WMAP data on small angular scales, we revisit the dipole modulated signal model introduced by Gordon et al. (2005). This model assumes that the true CMB 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, p. Previous analyses of this model has been restricted to very low resolution due to computational cost. In this paper, we double the angular resolution, and compute the full corresponding posterior distribution for the 5-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, non-zero at 3.3sigma, and the preferred direction points toward Galactic coordinates (l,b) = (224 degree, -22 degree) +/- 24 degree. The corresponding results for l <~ 40 from earlier analyses was A = 0.11 +/- 0.04 and (l,b) = (225 degree,-27 degree). The statistical significance of a non-zero amplitude thus increases from 2.8sigma to 3.3sigma when increasing l_max from 40 to 64, and all results are consistent to within 1sigma. Similarly, the Bayesian log-evidence difference with respect to the isotropic model increases from Delta ln E = 1.8 to Delta ln E = 2.6, ranking as "strong evidence" on the Jeffreys' scale. The raw best-fit log-likelihood difference increases from Delta ln L = 6.1 to Delta ln L = 7.3. 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 5-year WMAP data set, in agreement with the reports of Hansen et al. (2008).

Affiliated with

Also associated with

No associations

Rating

Increasing evidence for hemispherical power asymmetry in the five-year WMAP data does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Increasing evidence for hemispherical power asymmetry in the five-year WMAP data, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Increasing evidence for hemispherical power asymmetry in the five-year WMAP data will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-136131