Asymmetries in the Cosmic Microwave Background Anisotropy Field
Abstract
We report on the results from two independent but complementary statistical analyses of the Wilkinson Microwave Anisotropy Probe (WMAP) firstyear data, based on the power spectrum and Npoint correlation functions. We focus on large and intermediate scales (larger than about 3°) and compare the observed data against Monte Carlo ensembles with WMAPlike properties. In both analyses, we measure the amplitudes of the largescale fluctuations on opposing hemispheres and study the ratio of the two amplitudes. The powerspectrum analysis shows that this ratio for WMAP, as measured along the axis of maximum asymmetry, is high at the 95%99% level (depending on the particular multipole range included). The axis of maximum asymmetry of the WMAP data is weakly dependent on the multipole range under consideration but tends to lie close to the ecliptic axis. In the Npoint correlationfunction analysis, we focus on the northern and southern hemispheres defined in ecliptic coordinates, and we find that the ratio of the largescale fluctuation amplitudes is high at the 98%99% level. Furthermore, the results are stable with respect to choice of Galactic cut and also with respect to frequency band. A similar asymmetry is found in the COBE Differential Microwave Radiometer (DMR) map, and the axis of maximum asymmetry is close to the one found in the WMAP data.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 2004
 DOI:
 10.1086/382267
 arXiv:
 arXiv:astroph/0307507
 Bibcode:
 2004ApJ...605...14E
 Keywords:

 Cosmology: Cosmic Microwave Background;
 Cosmology: Observations;
 Methods: Statistical;
 Astrophysics
 EPrint:
 6 pages, 5 figures