Simulated 21 cm plus thermal noise input map (top), the GNILC reconstructed map and the respective residuals (middle), and the difference between the two (bottom), corresponding to a channel centered at 1115 MHz in the MD30 configuration. The maps are in celestial coordinates and are covered by the apodized Galactic mask defined in Sect. 3.2. The HI component was convolved with a FWHM = 40 arcmin beam.