| Abstract | We present new single-dish HI observations of 39 southern, extreme late- type spiral and irregular galaxies. These data are part of our continuing program aimed at obtaining a more complete census of the neutral gas content of optically identified, Local Supercluster galaxies for which no redshifts or HI data were previously available. We show that H I surveys concentrated on optically selected targets continue to be an effective means of surveying the gas in the local universe and furthering our knowledge of the properties of nearby galaxies. By focusing on galaxies with small angular sizes, low surface brightnesses, and very late-type morphologies, we find that we detect moderately low-M_HI_ galaxies within 10 Mpc, as well as a range of more distant, H I-rich systems. In spite of our limited detection sensitivity, we detected over 50% of our targets, implying that the majority of the objects in the faintest optically selected samples of late-type galaxies have at least moderate HI masses (detectable by our survey) and are not very low-M_HI_ dwarfs. Therefore, if large populations of very low-M_HI_, galaxies exist, they are not commonly found in optically selected, extreme late-type field samples. We find that most of our detected objects lie in previously defined groups or clouds, and we detect no objects in the direction of a nearby void. |
