TY - JOUR
T1 - Symmetry of the CMB sky as a new test of its statistical isotropy. Non cosmological octupole?
AU - Nasselski, Pavel
AU - Hansen, Martin Anders Kirstejn
AU - Kim, Jaiseung
PY - 2011/9/6
Y1 - 2011/9/6
N2 - In this article we propose a novel test for statistical anisotropy of the CMB ΔT( = (θ,φ)). The test is based on the fact, that the Galactic foregrounds have a remarkably strong symmetry with respect to their antipodal points S1: = -, = (θ,φ) and with respect to the Galactic plane, while the cosmological signal should not be symmetric or asymmetric under these transitions. We have applied the test for the octupole component of the WMAP ILC 7 map, by looking at a3,1 and a3,3, and their ratio to a3,2 both for real and imaginary values. We find abnormal symmetry of the octupole component at the level of 0.58%, compared to Monte Carlo simulations. By using the analysis of the phases of the octupole we found remarkably strong cross-correlations between the phases of the kinematic dipole and the ILC 7 octupole, in full agreement with previous results. We further test the multipole range 2 < l < 100, by investigating the ratio between the l+m = even and l+m = odd parts of power spectra. We compare the results to simulations of a Gaussian random sky, and find significant departure from the statistically isotropic and homogeneous case, for a very broad range of multipoles. We found that for the most prominent peaks of our estimator, the phases of the corresponding harmonics are coherent with phases of the octupole. We believe, our test would be very useful for detections of various types of residuals of the foreground and systematic effects at a very broad range of multipoles 2 l 1500-3000 for the forthcoming PLANCK CMB map, before any conclusions about primordial non-Gaussianity and statistical anisotropy of the CMB.
AB - In this article we propose a novel test for statistical anisotropy of the CMB ΔT( = (θ,φ)). The test is based on the fact, that the Galactic foregrounds have a remarkably strong symmetry with respect to their antipodal points S1: = -, = (θ,φ) and with respect to the Galactic plane, while the cosmological signal should not be symmetric or asymmetric under these transitions. We have applied the test for the octupole component of the WMAP ILC 7 map, by looking at a3,1 and a3,3, and their ratio to a3,2 both for real and imaginary values. We find abnormal symmetry of the octupole component at the level of 0.58%, compared to Monte Carlo simulations. By using the analysis of the phases of the octupole we found remarkably strong cross-correlations between the phases of the kinematic dipole and the ILC 7 octupole, in full agreement with previous results. We further test the multipole range 2 < l < 100, by investigating the ratio between the l+m = even and l+m = odd parts of power spectra. We compare the results to simulations of a Gaussian random sky, and find significant departure from the statistically isotropic and homogeneous case, for a very broad range of multipoles. We found that for the most prominent peaks of our estimator, the phases of the corresponding harmonics are coherent with phases of the octupole. We believe, our test would be very useful for detections of various types of residuals of the foreground and systematic effects at a very broad range of multipoles 2 l 1500-3000 for the forthcoming PLANCK CMB map, before any conclusions about primordial non-Gaussianity and statistical anisotropy of the CMB.
U2 - 10.1088/1475-7516/2011/09/012
DO - 10.1088/1475-7516/2011/09/012
M3 - Journal article
SN - 1475-7516
VL - 2011
SP - 012
JO - Journal of Cosmology and Astroparticle Physics
JF - Journal of Cosmology and Astroparticle Physics
IS - 09
ER -