Top left panel: enlarged image of the 2D map of the line-of-sight velocity of stars in the region of the HG. The iso-velocity contours are overlaid on the image, the minimum and maximum values are 2785 km s^-1 and 2960 km s^-1, with a step of about 6 km s^-1. The cross marks the centre of the galaxy where the systemic velocity is V = 2875 ± 3 km s^-1. The dashed lines indicate the photometric major and minor axes of the HG. Top right panel: high-frequency residual image obtained by the ratio of the original reduced r-band MUSE image with a smoothed one, where each original pixel value is replaced with the median value in a rectangular window of 25 × 25 pixels. Bottom left panel: enlarged image of the 2D map of the velocity field derived by the model. The dashed line indicates the direction of the HG minor axis PA = 157°. The iso-velocity contours are overlaid on the image, the minimum and maximum values are −145 km s^-1 and 145 km s^-1, with a step of about 13 km s^-1. See Sect. 4 for details. Bottom right panel: enlarged image of the 2D map of the line-of-sight velocity of gas in the regions close to centre of the galaxy. The iso-velocity contours are overlaid on the image, the minimum and maximum values are 2800 km s^-1 and 2920 km s^-1, with a step of about 6 km s^-1. In all images the cross marks the centre of the galaxy and north is up, east on the left.