21 cm Tomography with Foregrounds

Twenty-one centimeter tomography is emerging as a powerful tool to explorethe end of the cosmic dark ages and the reionization epoch, but it will only beas good as our ability to accurately model and remove astrophysical foregroundcontamination. Previous treatments of this problem have focused on the angularstructure of the signal and foregrounds and what can be achieved with limitedspectral resolution (bandwidths in the 1 MHz range). In this paper we introduceand evaluate a ``blind'' method to extract the multifrequency 21cm signal bytaking advantage of the smooth frequency structure of the Galactic andextragalactic foregrounds. We find that 21 cm tomography is typically limitedby foregrounds on scales $k\ll 1h/$Mpc and limited by noise on scales $k\gg1h/$Mpc, provided that the experimental bandwidth can be made substantiallysmaller than 0.1 MHz. Our results show that this approach is quite promisingeven for scenarios with rather extreme contamination from point sources anddiffuse Galactic emission, which bodes well for upcoming experiments such asLOFAR, MWA, PAST, and SKA.Comment: 10 pages, 6 figures. Revised version including various cases with high noise level. Major conclusions unchanged. Accepted for publication in Ap