A neutral hydrogen study of the barred spiral galaxy NGC 3319

Abstract

Neutral hydrogen line observations of the late-type barred spiral galaxy NGC 3319 are presented. The distribution and kinematics of the galaxy are studied using the Very Large Array,1 The Very Large Array is an instrument of the National Radio Astronomy Observatory, which is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation. with spatial resolutions between 11 and 50 arcsec, and a channel separation of 10.33 km s−1. As is typical for late-type galaxies, NGC 3319 is rich in H i, with a gaseous bar and spiral features. Several large, low-density regions are present, and the H i spiral structure is distorted, especially in the south. The gas distribution is asymmetric and extends significantly further to the south-east due to a long, off-centre tail. Non-circular motions caused by the bar, spiral structure and low-density regions are present in the radial velocity field, complicating the rotation curve analysis. These non-axisymmetric structures cause the values of the position angle and inclination derived from the velocity field to vary across the disc. In addition, beyond a radius of 180 arcsec, the velocity field is severely perturbed on the approaching (southern) side of the galaxy, and the disc becomes non-planar. However, the galaxy does not show the typical ‘integral sign’ shape of a warped system. We detect a small system approximately 11 arcmin (40 kpc) south of the centre of NGC 3319. It is seen in eight velocity channels and is coincident with a small, resolved object in the Palomar Sky Survey. A tidal interaction between this object and NGC 3319 is the most likely cause of the distorted spiral structure, the H i tail, and the velocity perturbations found in the southern half of the galaxy. Infalling tidal debris from such an event may account for the large, low-density regions found in the disc, several of which show kinematic evidence that suggest they are expanding superstructures. We are unable to determine the corotation radius from the H i velocity field using kinematic methods, but a break in the slope of the abundance gradient places it near the end of the bar. Star formation zones, as determined from an Hα image of the galaxy, are aligned with H i peaks and, except in the outermost optical disc, occur when the local H i density is in excess of 1.5×1021 cm−2.