Description of the masking process. Top left: map with the sum of all foregrounds considered in this work, including the synchrotron MD model (see Sect. 3.1), in the lowest frequency bin of a total of 30 channels centered on 984.7 MHz and limited to 10 K. Top right: result of applying the Galactic mask to the all-foregrounds map. Bottom left: BINGO apodized (5 deg) Galactic mask, preserving a sky fraction of 12.2%. Bottom right: result of applying the BINGO mask to the all-foregrounds map centered at 984.7 MHz. All maps are in celestial coordinates and the dashed lines delimit the BINGO covered area.