Rotational Widths for Use in the Tully-Fisher Relation. I. Long-Slit Spectroscopic Data

We present new long-slit Halpha spectroscopy for 403 non-interacting spiralgalaxies, obtained at the Palomar Observatory 5 m Hale telescope, which is usedto derive well-sampled optical rotation curves. Because many of the galaxiesshow optical emission features which are significantly extended along thespectrograph slit, a technique was devised to separate and subtract the nightsky lines from the galaxy emission. We exploit a functional fit to the rotationcurve to identify its center of symmetry; this method minimizes the asymmetryin the final, folded rotation curve. We derive rotational widths using bothvelocity histograms and the Polyex model fit. The final rotational width ismeasured at a radius containing 83% of the total light as derived from I-bandimages. In addition to presenting the new data, we use a large sample of 742galaxies for which both optical long-slit and radio HI line spectroscopy areavailable to investigate the relation between the HI content of the disks andthe extent of their rotation curves. Our results show that the correlationbetween those quantities, which is well-established in the case of HI-poorgalaxies in clusters, is present also in HI-normal objects: for a given opticalsize, star formation can be traced further out in the disks of galaxies withlarger HI mass.Comment: 16 pages, 6 figures. Full version of Table 1 and Figure 5 available as separate files. To appear in AJ (September 2005