Top row: on the left-hand panel the H i galactic emission, as derived from GBT observations, is shown (see text for details). On the right-hand panel, M 31 associated H i emission, obtained as the difference between the GBT map integrated over all the velocities, and the pure MW cirrus emission. Bottom row: on the left-hand panel the original SPIRE 250 μm image, convolved to the GBT resolution and matched to the same pixelsize, compared to the cirrus subtracted image, at the same resolution (right-hand side).