A technique for foreground subtraction in redshifted 21cm observations

Abstract

One of the main challenges for future 21cm observations is to remove foregrounds which are several orders of magnitude more intense than the H I signal. We propose a new technique for removing foregrounds of the redshifted 21cm observations. We consider multi-frequency interferometer observations. We assume that the 21cm signals in different frequency channels are uncorrelated and the foreground signals change slowly as a function of frequency. When we add the visibilities of all channels, the foreground signals increase roughly by a factor of ∼N because they are highly correlated. However, the 21cm signals increase by a factor of ∼√N because the signals in different channels contribute randomly. This enables us to obtain an accurate shape of the foreground angular power spectrum. Then, we obtain the 21cm power spectrum by subtracting the foreground power spectrum obtained this way. We describe how to obtain the average power spectrum of the 21cm signal. © 2012 The American Astronomical Society. All rights reserved.