Neutral hydrogen in IC 342. II. The detailed structure.

A study of H I in the Scd galaxy IC342 with a resolution in radial velocity of 16 km/s and with an angular resolution sufficient to resolve detailed spiral structure is presented. Spiral arms extend over the outer, warped parts of the disk, and reach the limit of detected H I at about 40 arcmin from the nucleus. The pattern is multiarmed, with the clearest features lying beyond the observed optical emission, and inner arms which are well correlated with other population material. A marginal detection of radial streaming motions above 5 km/s along one arm is consistent with the results presented and with the conclusion derived from the H I distribution that corotation is between 16 and 21 kpc from the nucleus, and the pattern speed is approximately 10 km/s/kpc.