We analyse new integral field spectroscopy of the inner region ( central 2.5 kpc ) of the spiral galaxy NGC 4321 to study the peculiar kinematics of this region .
Fourier analysis of the velocity residuals obtained by subtracting an axisymmetric rotation model from the H \alpha velocity field , indicates that the distortions are global features generated by an m = 2 perturbation of the gravitational potential which can be explained by the nuclear bar .
This bar has been previously observed in the near-infrared but not in the optical continuum dominated by star formation .
We detect the optical counterpart of this bar in the 2D distribution of the old stellar population ( inferred from the equivalent width map of the stellar absorption lines ) .
We apply the Tremaine–Weinberg method to the stellar velocity field to calculate the pattern speed of the inner bar , obtaining a value of \Omega _ { b } =160 \pm 70 km s ^ { -1 } kpc ^ { -1 } .
This value is considerably larger than the one obtained when a simple bar model is considered .
However the uncertainties in the pattern speed determination prevent us to give support to alternative scenarios .