H alpha kinematics of S(4)G spiral galaxies - I. NGC 864
We present a study of the kinematics of the isolated spiral galaxy NGC 864, using H alpha Fabry-Perot data obtained with the Galaxy H alpha Fabry-Perot System (GH alpha FaS) instrument at the William Herschel Telescope in La Palma, complemented with images at 3.6 mu m, in the R band and in H alpha filter, and integral-field spectroscopic data. The resulting data cubes and velocity maps allow the study of the kinematics of the galaxy, including in-depth investigations of the rotation curve, velocity moment maps, velocity residual maps, gradient maps and position-velocity diagrams. We find asymmetries in the velocity field in the bar zone, caused by non-circular motions, probably in response to the potential of the bar. We also find a flat-profile bar, in agreement with the strong bar, with the grand design spiral pattern, and with the gap between the ends of the bar and the start of the spiral arms. We quantify the rate of massive star formation, which is concentrated in the two spiral arms.