Detection of Non-Gaussianity in the Wilkinson Microwave Anisotropy Probe First-Year Data Using Spherical Wavelets

By Patricio Vielva, Enrique Martinez-Gonzalez, Rita Belén Barreiro, José Luis Sanz, L. Cayón. 2003

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A non-Gaussian detection in the Wilkinson Microwave Anisotropy Probe (WMAP) first-year data is reported. The detection has been found in the combined Q - V - W map proposed by the WMAP team after applying a wavelet technique based on the spherical Mexican hat wavelet (SMHW). The skewness and the kurtosis of the SMHW coefficients are calculated at different scales (ranging from a few arcminutes to tens of degrees). A non-Gaussian signal is detected at scales of the SMHW around 4° (size in the sky of around 10°). The right-tail probability of the detection is ≈0.4%. In addition, a study of Gaussianity is performed in each hemisphere. The northern hemisphere is compatible with Gaussianity, whereas the southern one deviates from Gaussianity with a right-tail probability of ≈0.1%. Systematics, foregrounds, and uncertainties in the estimation of the cosmological parameters are carefully studied in order to identify the possible source of non-Gaussianity. The detected deviation from Gaussianity is not found to be caused by systematic effects: (1) Each one of the Q, V, and W receivers shows the same non-Gaussianity pattern. (2) Several combinations of the different receivers at each frequency band—which highly reduce the cosmic microwave background (CMB) and the foreground emissions—do not show this non-Gaussian pattern. Similarly, Galactic foregrounds show a negligible contribution to the non-Gaussian detection: non-Gaussianity is detected in all the WMAP maps (from 23 to 94 GHz), and no frequency dependence is observed. Moreover, the expected foreground contribution to the combined WMAP map was added to CMB Gaussian simulations showing a behavior compatible with the Gaussian model. The influence of uncertainties in the CMB power spectrum estimation are also quantified. Hence, possible intrinsic temperature fluctuations (such as secondary anisotropies and primordial features) cannot be rejected as the source of this non-Gaussian detection. We remark that our result implies not only asymmetries north/south—like other previous WMAP analyses—but also a direct non-Gaussian detection.

Subfields: Astronomy and Astrophysics, Oceanography

View Paper: https://www.semanticscholar.org/paper/651841dd8fc825fa3b02b3cf62fc6c2b06f31bc1

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Citations in the corpus

Hemispherical Power Asymmetry in the Third-Year Wilkinson Microwave Anisotropy Probe Sky Maps (2007, background): “…multipoles (de Oliveira-Costa et al. 2004; Eriksen et al. 2004a), 2) an apparent asymmetry in the distribution of fluctuation power in two opposing hemispheres (Eriksen et al. 2004b; Hansen et al. 2004), and 3) a peculiar cold spot in the southern hemisphere (Vielva et al. 2004; Cruz et al. 2005).”
Directly Observing the Galaxies Likely Responsible for Reionization (2016, background): “…used in astronomy for purposes such as de-noising images (Starck et al. 2002), analyzing the clustering of galaxies (Slezak et al. 1993; Escalera & MacGillivray 1995; Martínez et al. 2005), and detecting non-Gaussianity in the cosmic microwave background (Starck et al. 2004; Vielva et al. 2004).”
The non‐Gaussian cold spot in Wilkinson Microwave Anisotropy Probe: significance, morphology and foreground contribution (2006, methodology): “…alignment statistics (Wiaux et al. 2006); multivariate analysis (Dineen & Coles 2005); Minkowski functionals (Park 2004, Eriksen et al. 2004b); gradient and dispersion analyses (Chyzy et al. 2005) or wavelets (Vielva et al. 2004, Mukherjee & Wang 2004, Cruz et al. 2005, McEwen et al. 2005).”
The Axis of Evil revisited (2006, neutral): “Reports of something awry have been obtained using a variety of techniques (e.g., Park (2004); Eriksen et al. (2004a); Hansen et al. (2004); Donoghue & Donoghue (2005); Land & Magueijo (2005a); Hansen et al. (2004); Eriksen et al. (2004b); Vielva et al. (2004)).”
Testing for Non-Gaussianity in the Wilkinson Microwave Anisotropy Probe Data: Minkowski Functionals and the Length of the Skeleton (2004, methodology): “…such signatures has arisen in recent months from putative detections of non-Gaussian features in the Wilkinson Microwave Anisotropy Probe (WMAP; Bennett et al. 2003a) first-year sky maps (Coles et al. 2004; Naselsky et al. 2003; Vielva et al. 2004; Copi et al. 2004; Park 2004; Eriksen et al. 2004).”
Spherical needlets for cosmic microwave background data analysis (2008, methodology): “…where statistical methods are required; a very incomplete list of references should include testing for non-Gaussianity (see Cabella et al. 2004; Vielva et al. 2004), foreground subtraction (Hansen et al. 2006), point source detection (Sanz et al. 2006), component separation (Moudden et al.…”
The Pantheon+ Analysis: Cosmological Constraints (2022, neutral): “The “CMB cold spot,” a 5° region of−70 μK centered at (l∼ 209°, b∼−57°), was first detected in data from the Wilkinson Microwave Anisotropy Probe (Vielva et al. 2004; Cruz et al. 2006), and subsequently in Planck data (Gurzadyan et al. 2014).”
Confronting Lemaitre–Tolman–Bondi models with observational cosmology (2008, background): “This should not come as a surprise, we do live in an (locally) inhomogeneous universe, some say that within a large underdense void [6, 7, 8, 9, 10, 11] similar to that which induces a cold spot in the CMB [ 12 , 13, 14] so why should we assume global homogeneity? In fact, the possibility that we ha”
Probing cosmic isotropy with a new X-ray galaxy cluster sample through the LX–T scaling relation (2020, background): “…(l, b) = (264◦,−17◦) and the unexpected quadrupole-octopole alignment and the existence of the Cold Spot at (l, b) = (210◦,−57◦) (Tegmark et al. 2003; Vielva et al. 2004; Kim & Naselsky 2010; Aluri & Jain 2012; Cai et al. 2014; Planck Collaboration XXIII 2014; Planck Collaboration XVI 2016;…”
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Detection of a non‐Gaussian spot in WMAP (2004, methodology): “Previous works such as Vielva et al. 2004, Eriksen et al. 2004a or Hansen 2004b have already reported North-South asymmetries, which are confirmed here.”
SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP ) OBSERVATIONS: ARE THERE COSMIC MICROWAVE BACKGROUND ANOMALIES? (2010, methodology): “Vielva et al. (2004) used a spherical Mexican hat wavelet (SMHW) analysis on the first year WMAP data to claim a detection of a non-Gaussian signal on a scale of a few degrees, independent of the WMAP observing frequency.”
FIVE-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE OBSERVATIONS: COSMOLOGICAL INTERPRETATION (2008, neutral): “…al. 2004, 2007a; Copi et al. 2004; Schwarz et al. 2004; Copi et al. 2006, 2007; Gordon et al. 2005; Bielewicz et al. 2005; Jaffe et al. 2005, 2006; Vielva et al. 2004; Cruz et al. 2005, 2006, 2007b,a; Cayón et al. 2005; Bridges et al. 2007; Wiaux et al. 2008; Räth et al. 2007; Land & Magueijo…”
POWER ASYMMETRY IN COSMIC MICROWAVE BACKGROUND FLUCTUATIONS FROM FULL SKY TO SUB-DEGREE SCALES: IS THE UNIVERSE ISOTROPIC? (2008, background): “The position of the non-Gaussian cold spot found in (Vielva et al. 2004b) is found to be positioned close to the center of the hemisphere with large fluctuation power.”
POWER ASYMMETRY IN WMAP AND PLANCK TEMPERATURE SKY MAPS AS MEASURED BY A LOCAL VARIANCE ESTIMATOR (2014, background): “…features in the data that hinted at possible violations of the statistical isotropy (see, e.g., Tegmark et al. 2003; de Oliveira-Costa et al. 2004; Vielva et al. 2004; Larson & Wandelt 2004; Land & Magueijo 2005a, 2005b, 2007; McEwen et al. 2005, 2006; Jaffe et al. 2006; Hinshaw et al. 2007;…”