Position-velocity diagrams of ionized gas in the inner regions of disk galaxies

We use long-slit spectroscopy along the major axis of a sample of 23 nearby disk galaxies to study the kinematic properties of the ionized-gas component in their inner regions. For each galaxy, we derive the position-velocity diagram of the ionized gas from its emission lines. We discuss the variety of shapes observed in such position-velocity diagrams by comparing the gas velocity gradient, velocity dispersion and integrated flux measured in the inner (r ≃ ±1″) and outer regions (r ≃ ±4″). This kind of analysis allows the identification of galaxies which are good candidates to host a circumnuclear Keplerian gaseous disk rotating around a central mass concentration, and to follow up with Hubble Space Telescope observations.