Wilkinson Microwave Anisotropy Probe Team Research Articles

Constraints on mode couplings and modulation of the CMB with WMAP data

We investigate a possible asymmetry in the statistical properties of the cosmic microwave background temperature field and to do so we construct an estimator aiming at detecting a dipolar modulation. Such a modulation is found to induce correlations between multipoles with $\ensuremath{\Delta}\ensuremath{\ell}=1$. We proceed in two steps. First, assuming that the only possible contaminant comes from our galaxy, we build an estimator using an azimuthally symmetric galactic mask for which analytical construction is possible. Applying this estimator to the V and W bands of the Wilkinson Microwave Anisotropy Probe (WMAP) data, we found an apparent detection in the V band. Further investigation of the foregrounds and the use of the kp0 mask provided by the WMAP team shows that, when the main extragalactic sources are properly removed, no significant detection remains.

TheN‐Point Correlation Functions of the First‐YearWilkinson Microwave Anisotropy ProbeSky Maps

We compute the two-, three- and four-point correlation functions from the Wilkinson Microwave Anisotropy Probe (WMAP) first-year data and compare these with a Monte Carlo ensemble of 5000 realizations based on the best-fit WMAP running-index spectrum of Gaussian fluctuations. The analysis is carried out in three steps, covering small (<72'), intermediate (<5°), and large scales (up to 180°). On the largest scales our results are consistent with the previously reported hemisphere power asymmetries: the northern ecliptic hemisphere is practically devoid of large-scale fluctuations, while the southern hemisphere shows relatively strong fluctuations. We also detect excess correlations in W-band difference maps as compared with the detailed noise simulations produced by the WMAP team, possibly indicative of unknown systematics. While unlikely to affect any temperature-based results, this effect could potentially be important for the upcoming polarization data. On intermediate angular scales we find hints of a similar anisotropic distribution of power as seen on the very largest scales, but not to the same extent. In general, the model is accepted on these scales. Finally, the same is also true on the smallest scales probed in this paper.

The Angular Power Spectrum of the First-Year Wilkinson Microwave Anisotropy Probe Data Reanalyzed

We measure the angular power spectrum of the Wilkinson Microwave Anisotropy Probe (WMAP) first-year temperature anisotropy maps. We use the Spatially Inhomogeneous Correlation Estimator (SpICE) to estimate Cl's for multipoles l = 2-900 from all possible cross-correlation channels. Except for the map-making stage, our measurements provide an independent analysis of that by G. Hinshaw et al. Despite the different methods used, there is virtually no difference between the two measurements for l 700; the highest l's are still compatible within 1 σ errors. We use a novel intrabin variance method to constrain Cl errors in a model-independent way. Simulations show that our implementation of the technique is unbiased within 1% for l 100. When applied to WMAP data, the intrabin variance estimator yields diagonal errors ~10% larger than those reported by the WMAP team for 100 < l < 450. This translates into a 2.4 σ detection of systematics, since no difference is expected between the SpICE and the WMAP team estimator window functions in this multipole range. With our measurement of the Cl's and errors, we get a χ2 per degree of freedom (dof) of 1.042 for a best-fit ΛCDM model, which has a 14% probability, whereas the WMAP team obtained χ2/dof = 1.066, which has a 5% probability. We assess the impact of our results on cosmological parameters using Markov chain Monte Carlo simulations. From WMAP data alone, assuming spatially flat power-law ΛCDM models, we obtain the reionization optical depth τ = 0.145 ± 0.067, spectral index ns = 0.99 ± 0.04, Hubble constant h = 0.67 ± 0.05, baryon density Ωbh2 = 0.0218 ± 0.0014, cold dark matter density ΩCDMh2 = 0.122 ± 0.018, and σ8 = 0.92 ± 0.12, consistent with a reionization redshift zre = 16 ± 5 (68% CL).

Microwave Interstellar Medium Emission Observed by theWilkinson Microwave Anisotropy Probe

We investigate the nature of the diffuse Galactic emission in the Wilkinson Microwave Anisotropy Probe (WMAP) temperature anisotropy data. Substantial dust-correlated emission is observed at all WMAP frequencies, far exceeding the expected thermal dust emission in the lowest frequency channels (23, 33, and 41 GHz). The WMAP team interprets this emission as dust-correlated synchrotron radiation, attributing the correlation to the natural association of relativistic electrons produced by supernovae (SNe) with massive star formation in dusty clouds, and deriving an upper limit of 5% on the contribution of Draine & Lazarian spinning dust to the K band (23 GHz). We pursue an alternative interpretation that much, perhaps most, of the dust-correlated emission at these frequencies is indeed spinning dust, and explore the spectral dependence on environment by considering a few specific objects as well as the full-sky average. Models similar to Draine & Lazarian spinning dust provide a good fit to the full-sky data. The full-sky fit also requires a significant component with a flat spectrum uncorrelated with Hα, possibly hot (~106 K) gas within 30° of the Galactic center.

On Foreground Removal from theWilkinson Microwave Anisotropy ProbeData by an Internal Linear Combination Method: Limitations and Implications

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.

Detection of Non‐Gaussianity in theWilkinson Microwave Anisotropy ProbeFirst‐Year Data Using Spherical Wavelets

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.

A polarized synchrotron template for cosmic microwave background polarization experiments based on WMAP data

We build template maps for the polarized Galactic synchrotron emission on large angular scales (7° full width at half maximum), in the 20-90 GHz microwave range, by using Wilkinson Microwave Anisotropy Probe (WMAP) data. The method, presented in recent work, requires a synchrotron total-intensity survey and the polarization horizon to model the polarized intensity and a starlight polarization map to model polarization angles. The basic template is obtained directly at 23 GHz with about 94 per cent sky coverage by using the synchrotron map released by the WMAP team. Extrapolations to 32, 60 and 90 GHz are performed by computing a synchrotron spectral-index map, which strongly reduces previous uncertainties in passing from low (1.4 GHz) to microwave frequencies. Differing from low-frequency data, none of our templates present relevant structures out of the Galactic plane. Our map at 90 GHz suggests that the synchrotron emission at high Galactic latitudes is low enough to allow robust detection of the E-mode component of the cosmological signal on large scale, even in models with low reionization (r = 0.05). Detection of the weaker B-mode on the largest scales (l 0.1. For lower levels of the gravitational-wave background the B-mode seems to be accessible only at the l ∼ 100 peak and in selected low-synchrotron emission areas.

The Quest for Microwave Foreground X

The Wilkinson Microwave Anisotropy Probe (WMAP) team has produced a foreground map that can account for most of the low-frequency Galactic microwave emission in the WMAP maps, tentatively interpreting it as emission. Finkbeiner and collaborators have challenged these conclusions, arguing that the WMAP team's synchrotron template is in fact dominated not by radiation but by some dust-related Galactic emission process, perhaps spinning dust grains, making dramatically different predictions for its behavior at lower frequencies. By cross-correlating this template with 10 and 15 GHz cosmic microwave background observations, we find that its spectrum turns over in a manner consistent with spinning dust emission, falling about an order of magnitude below what the interpretation would predict.

Significance of the largest scale CMB fluctuations in WMAP

We investigate anomalies reported in the cosmic microwave background maps from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite on very large angular scales and discuss possible interpretations. Three independent anomalies involve the quadrupole and octopole: (1) The cosmic quadrupole on its own is anomalous at the 1-in-20 level by being low (the cut-sky quadrupole measured by the WMAP team is more strikingly low, apparently due to a coincidence in the orientation of our Galaxy of no cosmological significance); (2) the cosmic octopole on its own is anomalous at the 1-in-20 level by being very planar; (3) the alignment between the quadrupole and octopole is anomalous at the 1-in-66 level. Although the a priori chance of all three occurring is 1 in 24000, the multitude of alternative anomalies one could have looked for dilutes the significance of such a posteriori statistics. The simplest small universe model where the universe has toroidal topology with one small dimension of order one-half the horizon scale, in the direction toward Virgo, could explain the three items above. However, we rule this model out using two topological tests: the S statistic and the matched circle test.

A maximum likelihood analysis of the low cosmic microwave background multipoles from theWilkinson Microwave Anisotropy Probe

The amplitudes of the quadrupole and octopole measured from the Wilkinson Microwave Anisotropy Probe (WMAP) appear to be lower than expected according to the concordance A cold dark matter (ACDM) cosmology. However, the pseudo-C l estimator used by the WMAP team is non-optimal. In this paper, we discuss the effects of Galactic cuts on pseudo-C l and quadratic maximum likelihood estimators. An application of a quadratic maximum likelihood estimator to Galaxy-subtracted maps produced by the WMAP team and Tegmark, de Oliveira-Costa & Hamilton shows that the amplitudes of the low multipoles are stable to different Galactic cuts. In particular, the quadrupole and octopole amplitudes are found to lie in the ranges ΔT 2 2 = 176-250 (μK) 2 and ΔT 2 3 = 794-1183 (μK) 2 (and more likely to be at the upper ends of these ranges) rather than the values ΔT 2 2 = 123 (μK) 2 and ΔT 2 3 = 611 (μK) 2 found by the WMAP team. These results indicate that the discrepancy with the concordance ACDM model at low multipoles is not particularly significant and is in the region of a few per cent. This conclusion is consistent with an analysis of the low amplitude of the angular correlation function computed from quadratic maximum likelihood power spectrum estimates.

High resolution foreground cleaned CMB map from WMAP

We perform an independent foreground analysis of the Wilkinson Microwave Anisotropy Probe (WMAP) maps to produce a cleaned cosmic microwave background (CMB) map (available online) useful for cross-correlation with, e.g., galaxy and x-ray maps. We use a variant of the Tegmark-Efstathiou technique that assumes that the CMB has a blackbody spectrum, but is otherwise completely blind, making no assumptions about the CMB power spectrum, the foregrounds, WMAP detector noise or external templates. Compared with the foreground-cleaned internal linear combination map produced by the WMAP team, our map has the advantage of containing less non-CMB power (from foregrounds and detector noise) outside the Galactic plane. The difference is most important on the angular scale of the first acoustic peak and below, since our cleaned map is at the highest ${(12.6}^{\ensuremath{'}})$ rather than lowest ${(49.2}^{\ensuremath{'}})$ WMAP resolution. We also produce a Wiener filtered CMB map, representing our best guess as to what the CMB sky actually looks like, as well as CMB-free maps at the five WMAP frequencies useful for foreground studies. We argue that our CMB map is clean enough that the lowest multipoles can be measured without any galaxy cut, and obtain a quadrupole value that is slightly less low than that from the cut-sky WMAP team analysis. This can be understood from a map of the CMB quadrupole, which shows much of its power falling within the Galaxy cut region, seemingly coincidentally. Intriguingly, both the quadrupole and the octopole are seen to have power suppressed along a particular spatial axis, which lines up between the two, roughly towards $(l,b)\ensuremath{\sim}(\ensuremath{-}110\ifmmode^\circ\else\textdegree\fi{},60\ifmmode^\circ\else\textdegree\fi{})$ in Virgo.

Faraday rotation as a diagnostic of Galactic foreground contamination of cosmic microwave background maps

We present a diagnostic test of possible Galactic contamination of cosmic microwave background (CMB) sky maps designed to provide an independent check on the methods used to compile these maps. The method involves a non-parametric measurement of cross-correlation between the Faraday rotation measure (RM) of extragalactic sources and the measured microwave signal at the same angular position. We argue that statistical properties of the observed distribution of rotation measures are consistent with a Galactic origin, an argument reinforced by a direct measurement of cross-correlation between the dust, free-free and synchrotron foreground maps and the RM values, with the strongest correlation being for dust and free-free. We do not find any statistically compelling evidence for correlations between the RM values and the COBE Differential Microwave Radiometer (DMR) maps at any frequency, so there is no evidence of residual contamination in these CMB maps. On the other hand, there is a statistically significant correlation of RM with the preliminary Wilkinson Microwave Anisotropy Probe (WMAP) individual frequency maps which remains significant in the Tegmark et al. Wiener-filtered map, but not in the internal linear combination map produced by the WMAP team.