A method for subtracting foregrounds from multifrequency CMB sky maps

An improved method for subtracting contaminants from Cosmic MicrowaveBackground (CMB) sky maps is presented, and used to estimate how well futureexperiments will be able to recover the primordial CMB fluctuations. We findthat the naive method of subtracting foregrounds (such as dust emission,synchrotron radiation, free-free-emission, unresolved point sources, etc) on apixel by pixel basis can be improved by more than an order of magnitude bytaking advantage of the correlation of the emission in neighboring pixels. Theoptimal multi-frequency subtraction method improves on simple pixel-by-pixelsubtraction both by taking noise-levels into account, and by exploiting thefact that most contaminants have angular power spectra that differsubstantially from that of the CMB. The results are natural to visualize in thetwo-dimensional plane with axes defined by multipole l and frequency v. Wepresent a brief overview of the geography of this plane, showing the regionsprobed by various experiments and where we expect contaminants to dominate. Weillustrate the method by estimating how well the proposed ESA COBRAS/SAMBAmission will be able to recover the CMB fluctuations against contaminatingforegrounds.