AN H(I) OPTICAL ATLAS OF H(II) GALAXIES AND THEIR COMPANIONS/

We have conducted a directed search for intergalactic H I clouds, usin g H II galaxies as pointers to fields on the sky likely to contain suc h clouds. This extends our previous survey (Taylor et al. 1993) by usi ng the VLA to map in the 21 cm line of H I a complete, volume-limited sample of H II galaxies. We detected 20 of the 21 galaxies in our samp le and find that 14 have nearby H I companions. Some H II galaxies hav e multiple companions, and we have discovered a total of 19 companions , or a frequency of occurrence of companions of 0.67. This detection r ate is statistically consistent with a lower limit of the companion fr equency of 0.46, assuming that no companions are present outside of th e spatial and velocity ranges searched by our VLA observations. The co mpanion population is not a homogeneous one but is comprised of H II g alaxies, cataloged and previously uncataloged dwarfs, and several obje cts for which there are no known optical counterparts. These latter ob jects may be intergalactic H I clouds. Here we present our H I maps an d R-band optical images of the H II galaxy and companion systems, alon g with physical properties determined from these data. We compare our sample to samples of H II galaxies from the literature, finding that t he literature samples overrepresent the more massive, more luminous H II galaxies. Our total mass estimates imply that H II galaxies are dom inated by dark matter, in agreement with observations of dwarf irregul ar galaxies. We also find a tendency for H II galaxies to be character ized by dense central H I concentrations surrounded by less dense enve lopes. Detailed analysis of the H II galaxy/companion systems will app ear in subsequent papers.