Influence of Planck foreground masks in the large angular scale quadrant CMB asymmetry

¹ CAS Key Laboratory for Researches in Galaxies and Cosmology, University of Sciences and Technology of China, Chinese Academy of Sciences, Hefei, 230026 Anhui, PR China
e-mail: larissa@ustc.edu.cn
² Università di Roma “Tor Vergata”, Dipartimento di Fisica, 00185 Rome, Italy
³ INFN, Sezione di Roma Tor Vergata, 00173 Rome, Italy
⁴ Instituto Nacional de Pesquisas Espaciais – INPE, Divisão de Astrofísica, 12227-010 São José dos Campos, SP, Brazil
⁵ State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, 100190 Beijing, PR China

Received: 10 June 2015
Accepted: 2 October 2015

Abstract

Context. The measured cosmic microwave background (CMB) angular distribution shows high consistency with the ΛCDM model, which predicts cosmological isotropy as one of its fundamental characteristics. However, isotropy violations were reported in CMB temperature maps of the Wilkinson Microwave Anisotropy Probe (WMAP) and confirmed by Planck satellite data.

Aims. Our purpose is to investigate the influence of different sky cuts (masks) employed in the analysis of CMB angular distribution, in particular in the excess of power in the southeastern quadrant (SEQ) and the lack of power in the northeastern quadrant (NEQ), found in both WMAP and Planck data.

Methods. We compared the two-point correlation function (TPCF) computed for each quadrant of the CMB foreground-cleaned temperature maps to 1000 Monte Carlo (MC) simulations generated assuming the ΛCDM best-fit power spectrum using four different masks, from the least to the most severe one: mask-rulerminimal, UT78, U73, and U66. In addition to the quadrants and for a better understanding of these anomalies, we computed the TPCF using the mask-rulerminimal for circular regions in the map where the excess and lack of power are present. We also compared, for completeness, the effect of Galactic cuts (+/−10, 20, 25, and 30 degrees above/below the Galactic plane) in the TPCF calculations as compared to the MC simulations.

Results. We found consistent results for three masks, namely mask-rulerminimal, U73, and U66. The results indicate that the excess of power in the SEQ tends to vanish as the portion of the sky covered by the mask increases and the lack of power in the NEQ remains virtually unchanged. A different result arises for the newly released UT78 Planck mask. When this mask is applied, the NEQ is no longer anomalous. On the other hand, the excess of power in the SEQ becomes the most significant one among the masks. Nevertheless, the asymmetry between the SEQ and NEQ is independent of the mask and it disagrees with the isotropic model with at least 95% C.L.

Conclusions. We find that UT78 disagrees with the other analyzed masks, especially when considering the SEQ and the NEQ individual analysis. Most important, the use of UT78 washes out the anomaly in the NEQ. Furthermore, we find an excess of kurtosis, compared with simulations, in the NEQ for the regions not masked by UT78 but masked by the other masks, indicating that the previous result could be due to unremoved residual foregrounds by UT78.