| Abstract | The H I content of the bright barred spiral galaxy NGC 3359 has been mapped with the VLA at a resolution of 18 arcsec (0.95 kpc) and 25 km/s. The neutral hydrogen is distributed in a grand-design, two-armed spiral pattern which dominates the large-scale structure. This H I spiral coincides very closely with the optical arms and the loci of H II regions, but extends to larger radii and is essentially bisymmetric, unlike the impression given by the rather patchy optical structure. On scales comparable to the synthesized beam, the gas is strongly clumped. Most of the total H I mass of 5 x 10 to the 9th solar mass is confined to a regularly bounded disk of radius 13.1 kpc, with some filamentary features extending to more than twice that distance from the nucleus. The velocity field of NGC 3359 exhibits large symmetric noncircular motions superposed on its rotation. The maxima of these disturbances are spatially coincident with the H I spiral arms, indicating that a density wave of large amplitude governs the global circulation of the gas in the disk of this galaxy. Streaming motions of at least 45 km/s are observed. The rotation curve rises to a maximum of 153 km/s at 11.2 kpc and then declines very slowly out to the last measured point at 21.6 kpc. The total mass within that radius is inferred to be 1.2 x 10 to the 11th solar mass. The observed kinematics suggest that the plane of the galaxy is not substantially warped at any radius. An extremely small and faint satellite galaxy has been discovered in this synthesis. Its global properties may be similar to those of the intergalactic H II regions, except that it is not observed in a phase of active star formation. |
