Properties of Bulgeless Disk Galaxies. I. Atomic Gas

We study the neutral hydrogen properties of a sample of 20 bulgeless disk galaxies (Sd-Sdm Hubble types), an interesting class that can be used to constrain galaxy formation and evolution, especially the role of mergers versus internal processes. Our sample is composed of nearby (within 32 Mpc), moderately inclined galaxies that bracket the circular velocity of 120 km s--1, which has been found to be associated with a transition in dust scale heights in edge-on, late-type disks. Here, we present H I channel maps, line profiles, and integrated intensity maps. We also derive kinematic parameters, including the circular velocity, from rotation curve analyses and calculate the integrated H I flux and H I mass for each galaxy in the sample. Three of the 20 galaxies in our sample have kinematically distinct outer components with major axes that differ by 30?-90? from the main disk. These distinct outer components may be due to a recent interaction, which would be somewhat surprising because the disks do not contain bulges. We will use the data products and derived properties in subsequent investigations into star formation and secular evolution in bulgeless disks with circular velocities above and below 120 km s--1.