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We model a 21 cm intensity mapping survey in the redshift range 0.01<z<1.5designed to simulate the skies as seen by future radio telescopes such as theSquare Kilometre Array (SKA), including instrumental noise and Galacticforegrounds. In our pipeline, we remove the introduced Galactic foregroundswith a fast independent component analysis (fastica) technique. We present thepower spectrum of the large-scale matter distribution, C(l), before and afterthe application of this foreground removal method and calculate the resultingsystematic errors. We attempt to reduce systematics in the foregroundsubtraction by optimally masking the maps to remove high foregrounds in theGalactic plane. Our simulations show a certain level of bias remains in thepower spectrum at all scales l<400. At large-scales l<30 this bias isparticularly significant. We measure the impact of these systematic effects intwo different ways: firstly we fit cosmological parameters to the broadbandshape of the power spectrum and secondly we extract the position of the BaryonAcoustic Oscillations (BAO). In the first analysis, we find that thesystematics introduce an significant shift in the best fit cosmologicalparameters at the 2 to 3 sigma level which depends on the masking and noiselevels. However, cosmic distances can be recovered in an unbiased way afterforeground removal at all simulated redshifts by fitting the BAOs in the powerspectrum. We conclude that further advances in foreground removal are needed inorder to recover unbiased information from the broadband shape of the powerspectrum, however, intensity mapping experiments will be a powerful tool formapping cosmic distances across a wide redshift range.

The effect of foreground subtraction on cosmological measurements from Intensity Mapping