The HI Companions of HII Galaxies and Low Surface Brightness Dwarf Galaxies

Abstract

I study the VLA HI survey of HII galaxies by Taylor et al. (1995, ApJS, 99, 427; 1996, ApJS, 102, 189) and the VLA HI survey of low surface brightness (LSB) dwarf galaxies by Taylor et al. (1996, ApJS, in press) to investigate the role of galaxy interactions in triggering the bursts of massive star formation seen in HII galaxies. I find that the companion rate for HII galaxies is more than twice that of LSB dwarfs (p[HII] = 0.57 p[LSB] = 0.24). I examine the completeness of the companion samples detected by the two surveys, finding that because they were observed in identical fashions, there are no relative biases to cause one sample or the other to have more companions. Thus I conclude that the difference in the number of HI rich companions is genuine, and signifies a difference in the local, small scale environments between the two types of galaxy. I search through published galaxy catalogs to study the large scale environments of the two samples, finding that at large separations, the two samples exist in very similar environments on average. The difference in companion rates between HII galaxies and LSB dwarfs supports the idea that the bursts of star formation are triggered by galaxy interactions.