Forecasting foreground impact on cosmic microwave background measurements

We explore the possible impact of galactic and extragalactic foregrounds on measurements of the cosmic microwave background (CMB). We find that, given our present understanding of the foregrounds, they are unlikely qualitatively to affect the ability of the MAP and Planck satellites to determine the angular power spectrum of the CMB, the key statistic for constraining cosmological parameters. Sufficiently far from the galactic plane, the only foregrounds that will affect power spectrum determination with any significance are the extragalactic ones. For MAP we find that the most troublesome foregrounds are radio point sources and the thermal Sunyaev–Zeldovich (SZ) effect. For Planck they are these same radio point sources and the far‐infrared background. Prior knowledge of the statistics of the SZ component (via either theoretical calculation, or higher‐frequency observations of just a few per cent of the sky, such as will be achieved by balloon‐borne experiments) may significantly improve MAP ’s determination of the CMB power spectrum. We also explore the foreground impact on MAP and Planck polarization power‐spectrum measurements.