Hemispherical Power Asymmetry in the Three-year Wilkinson Microwave Anisotropy Probe Sky Maps
نویسندگان
چکیده
We consider the issue of hemispherical power asymmetry in the three-year WMAP data, adopting a previously introduced modulation framework. Computing both frequentist probabilities and Bayesian evidences, we find that the model consisiting of an isotropic CMB sky modulated by a dipole field, gives a substantially better fit to the observations than the purely isotropic model, even when accounting for the larger prior volume. For the ILC map, the Bayesian log-evidence difference is ∼ 1.8 in favour of the modulated model, and the raw improvement in maximum log-likelihood is 6.1. The best-fit modulation dipole axis points toward (l, b) = (225◦,−27◦), and the modulation amplitude is 0.114, in excellent agreement with the results from the first-year analyses. The frequentist probability of obtaining such a high modulation amplitude in an isotropic universe is ∼ 1%. These results are not sensitive to data set or sky cut. Thus, the statistical evidence for a power asymmetry anomaly is both substantial and robust, although not decisive, for the currently available data. Increased sky coverage through better foreground handling and full-sky and high-sensitivity polarization maps may shed further light on this issue. Subject headings: cosmic microwave background — cosmology: observations — methods: statistical
منابع مشابه
A hemispherical power asymmetry from inflation
Measurements of cosmic microwave background temperature fluctuations by the Wilkinson Microwave Anisotropy Probe indicate that the fluctuation amplitude in one half of the sky differs from the amplitude in the other half. We show that such an asymmetry cannot be generated during single-field slow-roll inflation without violating constraints to the homogeneity of the Universe. In contrast, a mul...
متن کاملStatistical Isotropy of the Wilkinson Microwave Anisotropy Probe Data: a Bipolar Power Spectrum Analysis
The statistical expectation values of the temperature fluctuations of the cosmic microwave background (CMB) are assumed to be preserved under rotations of the sky. We use the bipolar power s pectrum (BiPS) proposed in Hajian & Souradeep to investigate the statistical isotropy (SI) of the CMB anisotropy maps recently measured by the Wilkinson Microwave Anisotropy Probe (WMAP). The method can iso...
متن کاملStatistical isotropy of CMB anisotropy from WMAP
The statistical expectation values of the temperature fluctuations of cosmic microwave background (CMB) are assumed to be preserved under rotations of the sky. We investigate the statistical isotropy of the CMB anisotropy maps recently measured by the Wilkinson Microwave Anisotropy Probe (WMAP) using bipolar spherical harmonic power spectrum proposed in Hajian & Souradeep 2003. The Bipolar Powe...
متن کاملStatistical Isotropy of the WMAP Data: A Bipolar Power Spectrum Analysis
The statistical expectation values of the temperature fluctuations of the cosmic microwave background (CMB) are assumed to be preserved under rotations of the sky. We investigate the statistical isotropy (SI) of the CMB anisotropy maps recently measured by the Wilkinson Microwave Anisotropy Probe (WMAP) using Bipolar Power Spectrum (BiPS) proposed in (Hajian & Souradeep 2003b). The method can p...
متن کاملMeasuring Statistical Isotropy of CMB Anisotropy
The statistical expectation values of the temperature fluctuations and polarization of cosmic microwave background (CMB) are assumed to be preserved under rotations of the sky. We investigate the statistical isotropy (SI) of the CMB maps recently measured by the Wilkinson Microwave Anisotropy Probe (WMAP) using the bipolar spherical harmonic formalism proposed in Hajian & Souradeep 2003 for CMB...
متن کامل