Effect of foregrounds on the cosmic microwave background radiation multipole alignment

Abstract

We analyse the effect of foregrounds on the observed alignment of the cosmic microwave background radiation (CMBR) quadrupole and octopole. The alignment between these multipoles is studied by using a symmetry‐based approach which assigns a principal eigenvector (PEV) or an axis with each multipole. We determine the alignment between these multipoles and its significance using the internal linear combination (ILC) 5‐ and 7‐yr maps. We also use the maps obtained by applying the internal power spectrum estimation (IPSE) procedure on the corresponding Wilkinson Microwave Anisotropy Probe data sets to assess its significance. The effect of foreground cleaning is studied in detail within the framework of the IPSE method both analytically and numerically. By using simulated CMBR data, including foregrounds and detector noise, we study how the PEVs of the simulated pure CMB maps differ from those of the corresponding clean maps. We find that, in general, the shift in the PEVs is relatively small and in random directions. Because of the random nature of the shift we conclude that the residual foregrounds can only lead to misalignment rather than cause alignment of multipoles. We also directly estimate the significance of the observed alignment by using simulated clean maps. We find that the results in this case are identical to those obtained by simple analytic estimates or by using simulated pure CMB maps.

Alignments of parity even/odd-only multipoles in CMB

“…These axes are shown in subsequent plots as some of the reference anisotropy directions seen in the CMB sky. Note that the alignment of CMB temperature quadrupole and octopole modes was found to improve by appying any additional corrections such as residual galactic bias correction (Aluri et al 2011) or kinetic quadrupole correction, frequency independent (Schwarz et al 2004) or frequency dependent . The PLANCK 2015 foreground cleaned maps have the frequency independent kinetic Doppler boost contribution subtracted (Planck Collaboration IX 2016).…”

Probing Statistical Isotropy of Cosmological Radio Sources using Square Kilometre Array

“…This is rather surprising! Furthermore, it is difficult to explain this alignment in terms of bias or foreground effects (Aluri et al, 2011). The procedure for extraction of the preferred direction has been developed in (de Oliveira-Costa et al, 2004;Ralston and Jain, 2004;Samal et al, 2008).…”

Searching for primordial non-Gaussianity in Planck CMB maps using a combined estimator

“…We begin the tests using just two classes, corresponding to MC CMB maps constructed using f NL = [−10, 10] (class = 1) and f NL = [40,60] (class = 2). We started using m = 1000 Area vectors (v i 0 , for i = 1, ..., 1000) for training the NN, 500 of each class.…”

“…Therefore, the test of the masks were performed applying the estimator to two sets of maps, each one composed by a different sky fraction. Both tests used three classes of maps, composed by a non-Gaussian signal such as f NL = [−10, 10] (class = 1), [28,48] (class = 2) and [60,80] (class = 3). The average hits resulting from these tests, that is the rate of successfully detection cases, are shown in Table 2.…”

“…These pixel noise maps are those corresponding to the SMICA, NILC, and SEVEM Planck maps, and the masks are the same used in the previous tests. Again it was used three classes of synthetic maps, constructed using the same ranges of f NL values used in previous analysis, that are: f NL = [−10, 10], [28,48] and [60,80]. Then, it was performed a total of four tests of the estimator, in four different sets of synthetic maps, that are: two sets of maps contaminated by SMICA noise, using 1) the U73 mask and 2) their own CS-mask, to analyze the influence of the two kinds of masks in the presence of the same noise, and two sets of maps contaminated with 3) SEVEM and 4) NILC noises, but using the same mask, U73, testing the impact of these two kinds of noise even with a rigorous sky cut.…”