Foregrounds and forecasts for the cosmic microwave background

One of the main challenges facing upcoming cosmic microwave background (CMB ) experiments will be to distinguish the cosmological signal from foregroun d contamination. We present a comprehensive treatment of this problem and s tudy how foregrounds degrade the accuracy with which the Boomerang, MAP, an d Planck experiments can measure cosmological parameters. Our foreground mo del includes not only the normalization, frequency dependence, and scale de pendence for each physical component, but also variations in frequency depe ndence across the sky. When estimating how accurately cosmological paramete rs can be measured, we include the important complication that foreground m odel parameters (we use about 500) must be simultaneously measured from the data as well. Our results are quite encouraging: despite all these complic ations, precision measurements of most cosmological parameters are degraded by less than a factor of 2 for our main foreground model and by less than a factor of 5 in our most pessimistic scenario. Parameters measured though large-angle polarization signals suffer more degradation: up to 5 in the ma in model and 25 in the pessimistic case. The foregrounds that are potential ly most damaging and therefore most in need of further study are vibrating dust emission and point sources, especially those in the radio frequencies. It is well known that E and B polarization contain valuable information ab out reionization and gravity waves, respectively. However, the crosscorrela tion between polarized and unpolarized foregrounds also deserves further st udy, as we find that it carries the bulk of the polarization information ab out most other cosmological parameters.