On the star-formation properties of emission-line galaxies in and around voids

We present a study of the star formation properties of a sample of emission line galaxies (ELGs) with respect to their environment. This study is part of a bigger project that aimed to find galaxies in voids and to investigate the large scale structure of the ELGs. A survey for ELGs was therefore conducted with the result that 16 galaxies have been found in very low density environments, of which 8 ELGs were found in two very well defined nearby voids. The sample presented here contains some galaxies identified in voids, as well as in the field environment that delimited the voids. These ELGs are all Blue Compact Galaxies (BCGs), and all void galaxies are also dwarfs. Both void and field sample contain the same mixture of morphological subtypes of BCDs, from the extreme Searle-Sargent galaxies to the Dwarf-Amorphous Nuclear-Starburst galaxies. The main result of this study is that field and void galaxies seem to have similar star formation rates (SFR), similar ratios between the current SFC and their average past SFR and similar mean SFR surface densities. There is no trend in metallicity, in the sense that void galaxies would have lower metallicities than their field counterparts. The field-cluster dichotomy is also discussed using available results from the literature, since our sample does not cover the cluster environment. The implication of our findings are discussed in connection with the theories for the formation and evolution of BCDs.