On Foreground Removal from the Wilkinson Microwave Anisotropy Probe Data by an Internal Linear Combination Method: Limitations and Implications

By H. Eriksen, A. Banday, K. G'orski, P. Lilje. 2004

218 citations recorded by the source corpus.

We study the Internal Linear Combination (ILC) method presented by the Wilkinson Microwave Anisotropy Probe (WMAP) science team, with the goal of determining whether it may be used for cosmological purposes, as a template-free alternative to existing foreground-correction methods. We conclude that the method does have the potential to do just that, but great care must be taken both in implementation and in a detailed understanding of limitations caused by residual foregrounds, which can still affect cosmological results. As a first step we demonstrate how to compute the ILC weights both accurately and efficiently by means of Lagrange multipliers, and we apply this method to the observed data to produce a new version of the ILC map. This map has 12% lower variance than the ILC map of the WMAP team, primarily because of less noise. Next we describe how to generate Monte Carlo simulations of the ILC map and find that these agree well with the observed map on angular scales up to l ≈ 200, using a conservative sky cut. Finally we make two comments to the ongoing debates concerning the large-scale properties of the WMAP data. First, we note that the Galactic southeastern quadrant is associated with notably different ILC weights than the other three quadrants, possibly indicating a foreground-related anisotropy. Second, we study the properties of the quadrupole and octopole (amplitude, alignment, and planarity) and reproduce the previously reported results that the quadrupole and octopole are strongly aligned and that the octopole is moderately planar. Even more interestingly, we find that the l = 5 mode is spherically symmetric at about 3 σ, and that the l = 6 mode is planar at the 2 σ level. However, we also assess the impact of residual foregrounds on these statistics, and find that the ILC map is not clean enough to allow for cosmological conclusions. Alternative methods must be developed to study these issues further.

Subfields: Astronomy and Astrophysics, Oceanography

View Paper: https://www.semanticscholar.org/paper/6037ef93f3f82b8e1499fac3b2c80cf8f99b2e9a

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In Astronomy and Astrophysics

1. A. Banday
2. K. G'orski
3. H. Eriksen
4. F. Hansen
5. D. Schwarz
6. P. Lilje
7. Glenn Starkman
8. C. Copi

In Oceanography

1. A. Banday
2. H. Eriksen
3. K. G'orski
4. F. Hansen
5. João Magueijo
6. K. Land
7. P. Lilje
8. Jean-François Cardoso

Citations in the corpus

• The pre-launch Planck Sky Model: a model of sky emission at submillimetre to centimetre wavelengths (2012, methodology): “In particular, CMB temperature maps have been obtained from publicly released WMAP data by a number of authors (e.g. Tegmark et al. 2003; Eriksen et al. 2004; Delabrouille et al. 2009; Basak & Delabrouille 2012).”
• Large-Angle Anomalies in the CMB (2010, methodology): “Most of the results discussed so far have been obtained using reconstructed full-sky maps of the WMAP observations [1, 22, 59].”
• INCREASING EVIDENCE FOR HEMISPHERICAL POWER ASYMMETRY IN THE FIVE-YEAR WMAP DATA (2009, methodology): “Some early notable examples include unexpected low-ℓ correlations (de Oliveira-Costa et al. 2004), a peculiar large cold spot in the southern Galactic hemisphere (Vielva et al. 2004), and a dipolar distribution of large-scale power (Eriksen et al. 2004a).”
• The Axis of Evil revisited (2006, methodology): “• In an anlaysis of the ILC map-making method, Eriksen et al. (2004) proposed a faster algorithm for the computation of the weights, that employs Lagrangian multipliers to linearize the problem.”
• Power Spectrum Estimation from High-Resolution Maps by Gibbs Sampling (2004, background): “However, the exact significance of this anomaly is dif-ficult to assess for several reasons, but mainly because of uncertainties in the foreground subtraction process (Eriksen et al. 2004; Slosar & Seljak 2004).”
• The non‐Gaussian cold spot in Wilkinson Microwave Anisotropy Probe: significance, morphology and foreground contribution (2006, background): “However also the TCM map presents complex noise properties (Eriksen et al 2004c).”
• CMB and SZ effect separation with constrained Internal Linear Combinations (2010, methodology): “…for foreground emission, has been extensively used in the analysis of the maps obtained by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite to extract a CMB map (Bennett et al. 2003; Eriksen et al. 2004; Park, Park & Gott 2007; Kim, Naselsky & Christensen 2008; Delabrouille et al. 2009).”
• POWER ASYMMETRY IN COSMIC MICROWAVE BACKGROUND FLUCTUATIONS FROM FULL SKY TO SUB-DEGREE SCALES: IS THE UNIVERSE ISOTROPIC? (2008, methodology): “…as well as other statistical anomalies were confirmed by several other authors using other methods (de Oliveira-Costa et al. 2004; Tegmark et al. 2003; Park 2004; Vielva et al. 2004b; Eriksen et al. 2004b; Land & Magueijo 2005a,b; Larson & Wandelt 2004; McEwen et al. 2005; Hansen et al. 2004b,c).”
• Evidence of Vorticity and Shear at Large Angular Scales in the WMAP Data: A Violation of Cosmological Isotropy? (2005, background): “To assess the statistical significance of the fits we compare our results to an ensemble of 10 000 LILC simulations, produced using the pipeline described by Eriksen et al. (2004b).”
• A full sky, low foreground, high resolution CMB map from WMAP (2008, methodology): “Eriksen et al. (2004) have obtained a CMB map at 1 degree resolution with another implementation of the ILC.”
• Detection of a non‐Gaussian spot in WMAP (2004, methodology): “Thereafter several other groups have found non-Gaussian signatures or asymmetries in the WMAP data (Park 2003, Eriksen et al. 2003, 2004a, Hansen et al. 2004a, b).”
• Hemispherical Power Asymmetry in the Third-Year Wilkinson Microwave Anisotropy Probe Sky Maps (2007, methodology): “Perhaps the three most important ones were: 1) alignments and symmetry features among low ℓ 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…”