Stacking detection map without re-gridding the cube. The background grey-scale image is the cube of the TNG50 520855 galaxy collapsed along the spectral axis and blanked from the galaxy emission. Black contours denote the noiseless moment 0 map clipped at the column density value of 3.6 × 10¹⁷ cm⁻². The coloured squares indicate the stacking regions where their stacked spectrum contains a reliable detection. Different colours represent different cell size: red for 9 × 9 and green for 5 × 5 beams.