Point source power in three-year Wilkinson Microwave Anisotropy Probe data

Using a set of multifrequency cross-spectra computed from the three year WMAP sky maps, we fit for the unresolved point source contribution. For a white noise power spectrum, we find a Q-band amplitude of A = 0.011 ± 0.001 μK sr (antenna temperature), significantly smaller than the value of 0.017±0.002 μK sr used to correct the spectra in the WMAP release. Modifying the point source correction in this way largely resolves the discrepancy Eriksen et al. (2006) found between the WMAP Vand W-band power spectra. Correcting the coadded WMAP spectrum for both the low-l power excess due to a sub-optimal likelihood approximation—also reported by Eriksen et al. (2006)—and the high-l power deficit due to over-subtracted point sources—presented in this letter—we find that the net effect in terms of cosmological parameters is a ∼ 0.7σ shift in ns to larger values: For the combination of WMAP, BOOMERanG and Acbar data, we find ns = 0.969±0.016, lowering the significance of ns 6= 1 from ∼ 2.7σ to ∼ 2.0σ. Subject headings: cosmic microwave background — cosmology: observations — methods: numerical