Asymmetries in the angular distribution of the cosmic microwave background

Abstract

Context. Intriguing features in the angular distribution of the cosmic microwave background (CMB), such as the north-south asymmetry, were reported in the one-and three-year Wilkinson Microwave Anisotropy Probe (WMAP) data and should be studied in detail. We investigate some of these asymmetries in the CMB temperature angular distribution considering the ΛCDM model in the three, five, and seven year WMAP data.Aims. We aim to analyze the four quadrants of the internal linear combination (ILC) CMB maps using three different Galactic cuts: the WMAP KQ85 mask, a |b| < 10 • Galactic cut, and the WMAP KQ85 mask + |b| < 10 • Galactic cut. Methods. We used the two-point angular correlation function (TPCF) in the WMAP maps for each of their quadrants. The same procedure was performed for 1000 Monte Carlo (MC) simulations that were produced using the WMAP team ΛCDM best-fit power spectrum. In addition, we changed the quadrupole and octopole amplitudes obtained from the ΛCDM model spectrum. We changed this to fit the quadrupole and octopole amplitudes to their observable values from the WMAP data. We repeated the analysis for the 1000 simulations of this modified ΛCDM model, hereafter MΛCDM. Results. Our analysis showed asymmetries between the southeastern quadrant (SEQ) and the other quadrants (southwestern quadrant (SWQ), northeastern quadrant (NEQ) and northwestern quadrant (NWQ)). Over all WMAP ILC maps, the probability for the occurrence of the SEQ-NEQ, SEQ-SWQ and SEQ-NWQ asymmetries varies from 0.1% (SEQ-NEQ) to 8.5% (SEQ-SWQ) using the KQ85 mask and the KQ85 mask + |b| < 10 • Galactic cut, respectively. We also calculated the probabilities for the MΛCDM using only the KQ85 mask and found no significant differences in the results. Moreover, the cold spot region located in the SEQ quadrant was covered with masks of 5, 10 and 15 degrees radius and again the results remained unchanged. Furthermore, this analysis was repeated for random regions in the SEQ quadrant with a 15-degree mask and the SEQ quadrant still remained asymmetric with respect to the other quadrants of the CMB map. Conclusions. We found an excess of power in the TPCF at scales >100 degrees in the SEQ with respect to the other quadrants that is independent of the Galactic cut used. Moreover, we tested a possible relation between the cold spot and the SEQ excess of power and found no evidence for it. Finally, we could not find any specific region within the SEQ that might be considered responsible for the quadrant asymmetry.

Quadrant asymmetry in the angular distribution of cosmic microwave background in thePlancksatellite data

“…Other unexpected features then emerged from the data, with examples including an alignment of the low order multipoles (Bielewicz et al 2004;Schwarz et al 2004;Copi et al 2004;de Oliveira-Costa et al 2004;Bielewicz et al 2005;Land & Magueijo 2005;Copi et al 2006;Abramo et al 2006;Frommert & Ensslin 2010;Gruppuso & Burigana 2009), the cold spot, which corresponds to a region with a significant temperature decrement (Vielva et al 2004;Cruz et al 2005Cruz et al , 2007Vielva 2010). More recently, the lack of large angle temperature correlations found previously on WMAP data were confirmed in Planck data by Copi et al (2013).The anomaly more related to this paper are the north-south asymmetry (Eriksen et al 2004a,b;Hansen et al 2004a,b;Donoghue et al 2005;Hoftuft et al 2009;Paci et al 2010;Pietrobon et al 2010;Vielva et al 2010) and the quadrant asymmetry (Santos et al 2012).…”

“…Taking into consideration that the occurrence of this asymmetry in the data (σ SEQ /σ NEQ ) can happen between any quadrant in the simulated maps, regardless of the different number of pixels in each quadrant because of the use of the mask, we found a probability of 0.8% for this asymmetry to happen (see Table 3, probability P3). It is important to point out that Santos et al (2012) found no evidence for a connection between the SEQ excess of power and the so-called cold spot anomaly (see Vielva et al 2004;Cruz et al 2005Cruz et al , 2007Vielva 2010).…”

“…(see Table 4). In Table 4, 1 It is important to point out that we used a different method from Santos et al (2012), found more appropriate, to calculate the mean values of the σ ratios. we can also see once again that the results are in agreement when WMAP KQ85 or Planck masks are used in the analysis.…”

“…It may then be interesting to repeat the statistical isotropy analysis done for WMAP, and previously for COBE, on Planck data. A&A 569, A75 (2014) The purpose of our study is to investigate the presence of quadrant asymmetry, which was detected in WMAP data by Santos et al (2012), in the Planck data using the two-point angular correlation function (TPCF). This result showed the existence of an excess of power, at angular distances between pixels above 90 degrees, in the southeastern quadrant (SEQ).…”

Influence ofPlanckforeground masks in the large angular scale quadrant CMB asymmetry

“…Other violations of isotropy were soon announced in WMAP data, including an alignment of the loworder multipoles (Bielewicz et al 2004(Bielewicz et al , 2005Schwarz et al 2004;Copi et al 2004Copi et al , 2006de Oliveira-Costa et al 2004;Land & Magueijo 2005;Abramo et al 2006;Gruppuso & Burigana 2009;Frommert & Ensslin 2010), the cold spot (Vielva et al 2004;Cruz et al 2005Cruz et al , 2007Vielva 2010), the parity asymmetry (Kim & Naselsky 2010;Gruppuso et al 2011;Aluri & Jain 2012;Hansen et al 2012;Naselsky et al 2012;Zhao 2014), and the north-south asymmetry (Eriksen et al 2004a,b;Hansen et al 2004a,b;Donoghue et al 2005;Hoftuft et al 2009;Paci et al 2010;Pietrobon et al 2010;Vielva et al 2010). Closely related to the north-south asymmetry is the power asymmetry found between different quadrants of the CMB sky (Santos et al 2012(Santos et al , 2014.…”