THE H-I COMPANIONS OF H-II GALAXIES AND LOW SURFACE BRIGHTNESS DWARF GALAXIES

I study the VLA H I survey of H II galaxies by Taylor et al. and the V LA H I survey of low surface brightness (LSB) dwarf galaxies by Taylor et al. to investigate the role of galaxy interactions in triggering t he bursts of massive star formation seen in H II galaxies. Comparing t he two surveys, I find that H II galaxies have companions more than tw ice as often as LSB dwarfs (p = 0.57 for II galaxies, compared to p = 0.24 for LSB dwarfs). I examine the completeness of the companion samp les detected by the two surveys. For the companions to H II galaxies, the sample is Likely complete in the distribution of velocity separati ons from their parent galaxies but is probably missing some companions at large projected linear separations because of the finite size of t he VLA primary beam. For the companions of LSB dwarfs, the small numbe r of detections means their distributions in velocity and linear separ ation are poorly determined, but the LSB dwarfs were observed with the same observational setup as the H II galaxies, so they will have the same levels of completeness. Because the two samples were observed in exactly the same fashion, there will be no relative bias in the number of companions introduced in this way. In addition, the redshift distr ibutions of the two samples are very similar, so there will not be a d istance-related relative bias. Thus, I conclude that the difference in the number of H I rich companions is genuine, and signifies a differe nce in the local, small-scale environments between the two types of ga laxy, I search through published galaxy catalogs to determine number o f neighbors each galaxy has outside the area of the VLA observations. At these large separations, the number of neighbors is the same, withi n the errors, for the two types of galaxy. The high rate of companion occurrence at low separations for H II galaxies relative to LSB dwarfs supports the hypothesis that the bursts of star formation are trigger ed by galaxy interactions.