Sky maps without anisotropies in the cosmic microwave background are a better fit to WMAP’s uncalibrated time-ordered data than the official sky maps

The purpose of this reanalysis of the WMAP uncalibrated time-ordered data (TOD) is twofold. The first is to reassess the reliability of the detection of the anisotropies in the official WMAP sky maps of the cosmic microwave background (CMB). The second is to assess the performance of a proposed criterion in avoiding systematic errors in detecting a signal of interest. The criterion is implemented by testing the null hypothesis that the uncalibrated TOD is consistent with no anisotropies when WMAP’s hourly calibration parameters are allowed to vary. It is shown independently for all 20 WMAP channels that sky maps with no anisotropies are a better fit to the TOD than those from the official analysis. The recently launched Planck satellite should help sort out this perplexing result. Copyright c © EPLA, 2009 Introduction. – The measurement of anisotropies in the cosmic microwave background (CMB) is of great interest to astronomers. The sky maps generated by the WMAP mission are widely considered to be the best measurements of the reported anisotropies [1–3]. The measurements of the CMB made by the WMAP satellite did not directly measure the intensity of the CMB at each point in the sky. Rather, each sky map of the CMB was reconstructed from hundreds of millions of differential measurements, usually referred to as the time-ordered data (TOD). Image reconstruction, including calibration of the TOD, was used to reconstruct the sky maps from the TOD. The CMB is widely believed to have been radiated by the universe when it was about 400000 years old. Therefore, any variation in the intensity of the CMB with direction in the sky would provide priceless information on the early universe. The CMB has been shown to have a nearly perfect black-body spectrum with a temperature of 2.726K [4]. Black bodies with this temperature radiate in the 60–630GHz range with a peak frequency of about (a)E-mail: [email protected] 160GHz. Also, the CMB has a nearly uniform intensity with direction. The WMAP sky maps. A sky map is an intensity plot of radiation in all directions at a particular frequency (fig. 1). At the galactic equator is the signal generated by the dust and gas in our Galaxy that obscures the CMB that is called the galactic band. Our Solar System’s relative motion to the CMB of about 369 km/s introduces a small but smooth variation in the intensity of the CMB, usually referred to as the dipole, at about 1 part in 10000 [1]. Given the relative motion is precisely known, the exact intensity of the dipole can be predicted [5] and easily subtracted off the CMB. Any variations in the intensity of the CMB after the subtraction are referred to as anisotropies. The reported anisotropies have intensity variations roughly 10 to 20 times smaller than those of the dipole. Thus, highly sensitive and well-calibrated instrumentation is needed to reliably measure the reported anisotropies. Figure 1 shows the sky map generated by the official WMAP analysis of the 5 year data for the 94GHz frequency band both with and without the dipole subtracted. For display purposes only, the sky map has