Low resolution HI map (the beam size of 72″ × 62″) superimposed on an optical image of M 74. The position of SN 2002ap is marked as the red dot (credit: Kamphuis & Briggs 1992, reproduced with permission © ESO). Left: zeroth moment map (integrated emission). Right: first moment map (velocity fields). The asymmetric tail with an irregular velocity field is visible at the south-western outskirt of the atomic disc (around the position of RA = 1^h33^m20^s, Dec = 15° 25^m). North is up and east is to the left.