The Local Environment of HII Galaxies

We have carried out an investigation of the environments of low redshift HII galaxies by cross-correlating their positions on the sky with those of faint field galaxies in the Automatic Plate Measuring Machine catalogues. We address the question of whether violent star formation in HII galaxies is induced by low mass companions by statistically estimating the mean space density of galaxies around them. We argue that even if low mass companions were mainly intergalactic HI clouds, their optical counterparts should be detectable at faint limits of the APM scans. A significantly positive signal is detected for the HII galaxy-APM galaxy angular cross-correlation function, but the amplitude is poorly determined. The projected cross-correlation function has higher signal-to-noise, and suggests that the amplitude is slightly lower than for normal field galaxies. This implies that these bursting dwarf galaxies inhabit slightly lower density environments to those of normal faint field galaxies, consistent with other studies of emission line galaxies. This suggests that in these dwarf starburst galaxies, star formation is not triggered by unusually strong tidal interactions, and must have a different origin.