Rotational widths for use in the Tully-Fisher relation. I. Long-slit spectroscopic data

We present new long-slit H alpha spectroscopy for 403 noninteracting spiral galaxies, obtained at the Palomar Observatory 5 m Hale telescope, which is used to derive well-sampled optical rotation curves. Because many of the galaxies show optical emission features that are significantly extended along the spectrograph slit, a technique was devised to separate and subtract the night sky lines from the galaxy emission. We exploit a functional fit to the rotation curve to identify its center of symmetry; this method minimizes the asymmetry in the final, folded rotation curve. We derive rotational widths using both velocity histograms and the Polyex model fit. The final rotational width is measured at a radius containing 83% of the total light as derived from I-band images. In addition to presenting the new data, we use a large sample of 742 galaxies for which both optical long-slit and radio H I line spectroscopy are available to investigate the relation between the H I content of the disks and the extent of their rotation curves. Our results show that the correlation between those quantities, which is well established in the case of H I-poor galaxies in clusters, is present also in H I-normal objects: for a given optical size, star formation can be traced farther out in the disks of galaxies with larger H I mass.