We have obtained optical CCD spectroscopy along the major axes of 22 nearby spiral galaxies of Sb and Sc types in order to analyze their rotation curves. By subtracting the stellar continuum emission, we have obtained position–velocity (PV) diagrams of the Hα and [N II] lines. We point out that the Hα line is often superposed by a broad stellar absorption feature (Balmer wing) in the nuclear regions, and, therefore, the [N II] line is a better tracer of kinematics in the central few hundred parsec regions. By applying the envelope-tracing technique to the Hα and [N II] PV diagrams, we have derived nucleus-to-disk rotation curves of the observed galaxies. The rotation curves rise steeply within the central few hundred parsecs, indicating a rapidly rotating nuclear disk and mass concentration near the nucleus.
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A 1998 study studied this question.