The velocity field of NGC 4258.

A determination of the velocity field of NGC 4258 is reported, derived from slit spectra obtained with the Hale 200-inch (5-m) and 60-inch (1. 5-m) telescopes at Palomar Mountain. The central region, the normal spiral arms, and the anomalous Ha arms have been covered, and a final velocity contour map is given in a figure, where the accuracy is somewhat better than one contour unit (50 km ) It is shown that the motions in the normal arms are consistent with pure rotation when new values are adopted for the position angle of the line of nodes (146 ) and the inclination (72 . These are consistent with the outline of faint outer arms and the distribution of neutral hydrogen derived in Westerbork. An approximate "basic" rotation curve is adopted, and an analysis of the velocity field then indicates that if no motion perpendicular to the plane is important, the Ha arms rotate considerably more slowly, and in the regions around the minor axis contractions occur. These observations are consistent with the predictions of a model proposed earlier by van der Kruit, Oort, and Mathewson in connection with radio-continuum observations. Subject headings: galaxies, individual - galaxies, motions in