First-year Wilkinson Microwave Anisotropy Probe (WMAP) observations:: Galactic signal contamination from sidelobe pickup

Since the Galactic center is similar to1000 times brighter than fluctuations in the cosmic microwave background (CMB), CMB experiments must carefully account for stray Galactic pickup. We present the level of contamination due to sidelobes for the first-year CMB maps produced by the Wilkinson Microwave Anisotropy Probe (WMAP) observatory. For each radiometer, full 4pi sr antenna gain patterns are determined from a combination of numerical prediction and ground-based and space-based measurements. These patterns are convolved with the WMAP first-year sky maps and observatory scan pattern to generate the expected sidelobe signal contamination, for both intensity and polarized microwave sky maps. When the main beams are outside of the Galactic plane, we find rms values for the expected sidelobe pickup of 15, 2.1, 2.0, 0.3, and 0.5 muK for the K, Ka, Q, V, and W bands, respectively. Except for at the K band, the rms polarized contamination is much less than1 muK. Angular power spectra of the Galactic pickup are presented.