Point Sources in theWilkinson Microwave Anisotropy ProbeSky Maps

We discuss point-source foregrounds for the Wilkinson Microwave Anisotropy Probe ( WMAP ) experiment. We consider several possible strategies for removing them and we assess how the statistics of the cosmic microwave background (CMB) signal are affected by the residual sources. Assuming a power-law distribution for the point sources, we propose a method aimed at determining the slope of the distribution from the analysis of the moments of the observed maps. The same method allows for a determination of the underlying CMB variance. We conclude that the best strategy for finding point sources is the simultaneous thresholding of the filtered map at all frequencies, with a relatively low threshold. With this strategy, we expect to find 70% (95%) of the sources above 3 (4) σ. Assuming the most conservative case for point-source detection, the recovered slope of the point-source distribution is 2.55 ± 0.15, for a fiducial n = 2.5 value. The recovered CMB plus noise map variance is within 0.2% from the real one, with a standard deviation of 0.31%, while cosmic variance contributes 2.2% to the same CMB plus noise map.