Erasing the Milky Way: new cleaning technique applied to GBT intensity mapping data

We present the rst application of a new foreground removal pipeline to the current leading HI intensity mapping dataset, obtained by the Green Bank Telescope (GBT). We study the 15hr and 1hr eld data of the GBT observations previously presented in Masui et al. (2013) and Switzer et al. (2013) covering about 41 square degrees at 0:6 < z < 1:0 which overlaps with the WiggleZ galaxy survey employed for the cross-correlation with the maps. In the presented pipeline, we subtract the Galactic foreground continuum and the point source contaminations using an independent component analysis technique (fastica) and develop a description for a Fourier-based optimal weighting estimator to compute the temperature power spectrum of the intensity maps and cross-correlation with the galaxy survey data. We show that fastica is a reliable tool to subtract diuse and point-source emission by using the non-Gaussian nature of their probability functions. The power spectra of the intensity maps and the cross-correlation with WiggleZ is typically an order of magnitude higher than the previous ndings by the GBT team. fastica is a very conservative subtraction technique and is not able to remove anisotropic noise contaminations caused by instrumental systematics unlike the singular value decomposition method which does not discriminate components according to their statistical properties. We conrm that foreground subtraction with fastica is robust against 21cm signal loss as seen by the converged amplitude of the cross-correlation of the intensity maps with the WiggleZ data.