Dipartimento di Astronomia, Università di Padova, vicolo dell'Osservatorio 2, 35122 Padova, Italy
2 European Southern Observatory, 3107 Alonso de Cordova, Santiago, Chile
3 Vatican Observatory, University of Arizona, Tucson, AZ 85721, USA
Corresponding author: L. Coccato, email@example.com
Accepted: 25 November 2003
We present the ionized-gas kinematics and photometry of a sample of 4 spiral galaxies which are characterized by a zero-velocity plateau along the major axis and a velocity gradient along the minor axis, respectively. By combining these new kinematical data with those available in the literature for the ionized-gas component of the S0s and spirals listed in the Revised Shapley-Ames Catalog of Bright Galaxies we realized that about of unbarred galaxies show a remarkable gas velocity gradient along the optical minor axis. This fraction rises to about if we include unbarred galaxies with an irregular velocity profile along the minor axis. This phenomenon is observed all along the Hubble sequence of disk galaxies, and it is particularly frequent in early-type spirals. Since minor-axis velocity gradients are unexpected if the gas is moving onto circular orbits in a disk coplanar to the stellar one, we conclude that non-circular and off-plane gas motions are not rare in the inner regions of disk galaxies.
Key words: galaxies: kinematics and dynamics / galaxies: elliptical and lenticular, cD / galaxies: spiral / galaxies: structure
Based on observations carried out at the European Southern Observatory in La Silla (Chile) (ESO 69.B-0706 and 70.B-0338), with the Multiple Mirror Telescope which is a joint facility of the Smithsonian Institution and the University of Arizona, and with the Italian Telescopio Nazionale Galileo (AOT-5, 3-18) at the Observatorio del Roque de los Muchachos in La Palma (Spain).
© ESO, 2004