High-resolution, high signal-to-noise, global H I spectra of southern, extreme late-type spiral galaxies

We have used the Nancay decimetric radio telescope to obtain high-resolution, high signal-to-noise, global H I spectra of 30 southern, extreme late-type spiral galaxies with V(h) less than or equal to 3000 km s(-1). For all of the galaxies we measure new precise radial velocities and H I velocity widths. Optical imaging and photometry of these galaxies was recently published by Matthews & Gallagher. In Appendix B we present new H I spectra for four additional late-type galaxies. The H I spectra of the extreme late-type spirals have velocity widths characteristic of true, rotationally supported disk galaxies, and most are double-peaked. Nonetheless, the morphologies of the H I profiles are diverse, indicating that disk galaxies with similar H I contents and optical luminosities can have very different H I distributions and/or velocity fields. H I profile type and Hubble type are generally well-correlated for our sample. Seventy-seven percent of our H I profiles show at least some degree of asymmetry; in many cases the stellar disk of these galaxies is also asymmetric. Several of our spectra have an additional H I peak near the systemic velocity, perhaps indicating a gas enhancement in the central regions of the galaxy disk.