21 cm Tomography with Foregrounds

Twenty-one centimeter tomography is emerging as a powerful tool to explore the reionization epoch and cosmological parameters, but it will only be as good as our ability to accurately model and remove astrophysical foreground contamination. Previous treatments of this problem have focused on the angular structure of the signal and foregrounds and what can be achieved with limited spectral resolution (channel widths in the 1 MHz range). In this paper we introduce and evaluate a "blind" method to extract the multifrequency 21 cm signal by taking advantage of the smooth frequency structure of the Galactic and extragalactic foregrounds. We find that 21 cm tomography is typically limited by foregrounds on scales of k ≪ 1 h Mpc^-1 and is limited by noise on scales of k ≫ 1 h Mpc^-1, provided that the experimental channel width can be made substantially smaller than 0.1 MHz. Our results show that this approach is quite promising even for scenarios with rather extreme contamination from point sources and diffuse Galactic emission, which bodes well for upcoming experiments such as LOFAR, MWA, PAST, and SKA.