Nearly Full-sky Low-multipole Cosmic Microwave Background Temperature Anisotropy. III. Cosmic Microwave Background 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 ∼3 σ for the Planck common mask with 26% masked fraction to ∼2 σ for the 1% mask. We find good agreement between the two sky cuts for the low northern variance, ∼3 σ , and the parity asymmetry, ∼2 σ . For the quadrupole-octopole alignment, we find good agreement between the 1% mask result and the full-sky results in the literature, ∼3 σ . 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 Λ cold dark matter (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.