Arecibo HI Mapping of a Large Sample of Dwarf Irregular Galaxies

Abstract

Neutral hydrogen mapping of 70 dwarf irregular (Sm, Im and BCD) galaxies is reported, with position-velocity contour maps presented for those resolved by the Arecibo beam. The galaxies were selected either from the Virgo Cluster Catalog, from similarly identified field galaxies, or from a distance-limited sample within the Arecibo declination range. We do not find any isolated dwarfs with a larger HI to optical radius ratio than DDO 154; the ``protogalaxy'' HI 1225+01 (Giovanelli \& Haynes 1989) continues to be a unique object among dwarfs that have been mapped in HI. For all dwarfs with significant rotation we are able to determine the sense of the spin. For a number of better-resolved dwarfs we are able to determine rotation curves, in most cases extending well beyond the last measured point in available synthesis array maps. Correlations among the several measures of galaxy size and mass are studied; in Paper II (Salpeter \& Hoffman 1996) we combine these data with those for the set of all available mapped dwarf irregular galaxies and for mapped spirals spanning a similar range of redshifts to investigate variations in Tully-Fisher relations and in surface densities as functions of galaxy size and luminosity or mass.