The Morphology of HII Galaxies

We present CCD images of a sample of 39 HII galaxies taken at the Danish 1.54m telescope on La Silla. The images are used to analyse the morphology of these emission line dwarfs, and the structural properties of the knots of star formation and of the underlying galaxy. The sizes of the starbursts are measured. We propose a morphological classification based on the presence or absence of signs of tails, extensions, or distorted outer isophotes. This criterion segregates the objects into two broad morphological types with different physical properties: the more disturbed and extended (type I) HII galaxies having larger luminosities and velocity dispersions than the more compact and regular (type II) objects. The relative position of HII galaxies and of a sample of dwarf elliptical galaxies in the [R -- sigma] diagram support the hypothesis of a possible evolutionary link between the two types of galaxy.