Neutral hydrogen in IC 342 - II. The detailed structure

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Abstract
H I in the Scd galaxy IC342 has been studied with a resolution in radial velocity of 16 km s–1 and with an angular resolution (1.9 × 2.0 arcmin) sufficient to resolve detailed spiral structure. Spiral arms extend over the outer, warped parts of the disc, and reach the limit of detected H I at ∼ 40 arcmin (50 kpc) from the nucleus. The pattern is multi-armed, with the clearest features lying beyond the observed optical emission, and inner arms which are well correlated with other Population I material. If the arms are quasi-stationary density-wave features, the absence of radial streaming motions > 5 km s–1 implies a small pattern speed. A marginal detection of such motions along one arm is consistent both with this result 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 ∼ 10 km s–1 kpc–1.

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