Nearly full-sky low-multipole CMB temperature anisotropy: III. CMB anomalies

Abstract

Unexpected features have been observed in the cosmic microwave background (CMB) temperature on large scales. We revisit these CMB anomalies using new foreground-cleaned CMB temperature maps derived in a companion paper from WMAP and Planck data, which are tailored to low-resolution analysis and require only minimal masking of $1\%$ of the sky. These maps allow us to assess the impact of foreground-cleaning methods and the choice of sky cut on the significance of five commonly studied CMB anomalies. We find a notable impact of the choice of galactic mask on the significance of two anomalies: the significance of the low real-space correlation function and of the local-variance asymmetry reduces from $\sim3\sigma$ for the Planck common mask with $26\%$ masked fraction to $\sim2\sigma$ for the $1\%$ mask. We find good agreement between the two sky cuts for the low northern variance, $\sim3\sigma$, and the parity asymmetry, $\sim2\sigma$. For the quadrupole-octopole alignment, we find good agreement between the $1\%$-mask result and the full-sky results in the literature, $\sim3\sigma$. Thus using a larger fraction of the sky enabled by improved foreground cleaning reduces the significance of two commonly studied CMB anomalies. Overall, for an alternative physical model to be convincingly favored over $\Lambda$CDM with statistically-isotropic Gaussian fluctuations, it would need to explain multiple CMB anomalies, or better describe some other type of measurement in addition to a CMB anomaly.