Correlations from Galactic Foregrounds in the First-Year Wilkinson Microwave Anisotropy Probe Data

We study a specific correlation in the spherical harmonic multipole domain for cosmic microwave background (CMB) analysis. This group of correlations between l = 2n, where n = 1,2,..., is caused by a symmetric signal in the Galactic coordinate system. A phase filter targeting such correlation therefore helps remove the localized bright pointlike sources in the Galactic plane and the strong diffuse component down to the CMB level. We illustrate the significance of these correlations and apply this estimator on some derived CMB maps with foreground residuals. In addition, we show that our proposed estimator significantly damps the phase correlations caused by Galactic foregrounds. This investigation provides understanding of mode correlations caused by Galactic foregrounds, which is useful for paving the way for foreground-cleaning methods for the CMB.