Left and middle: profiles of tangential and radial velocity of M 99. Shaded area indicates the 1σ rms from the fittings. A green solid line represents the fitting for the whole disk, while blue dotted and red crossed circles are respectively the results for the approaching and receding sides fitted separately. Right panel: Hα velocity dispersion of M 99. Symbols represent the observed dispersion; the dashed line is a smooth model of the observation used to derive the asymmetric drift.