Measuring galaxy distances from optical rotation curves

We describe a distance indicator for spiral galaxies using detailed rotation curves derived from Hα velocity fields and I band CCD photometry. Two-dimensional velocity fields are obtained with an imaging Fabry-Perot spectrometer with a velocity accuracy of better than 10 km/s. Rotation curves, based upon rotating disks geometries, are fit to these velocity fields. We present the I band photometry profiles, and the individual rotation curves for 75 galaxies. The extracted circular velocity is combined with I band magnitudes to form a Tully-Fisher relation, with a scatter of ~0.25^m^-0.3^m^ mag. We discuss in some detail the accuracy of our photometric measures, the merits of the detailed rotation curve solutions and the resultant effects on the scatter in the Tully-Fisher relation. As an example, we use the data to derive the relative distance modulus between the Hydra and Antlia clusters which yields a peculiar motion for Antlia of 900+/-100 km s^-1^. This confirms previous detections of large peculiar motions in the Hydra-Centaurus region.