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 con- ducted 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 con- tains 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 mor- phological 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 be- tween the current SFR 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. towards nearby voids, with the aim of finding faint galaxies within the voids. This was motivated by the question of whether the void regions represent real structures, or whether they merely appear as such due to selection effects. According to some theo- ries of galaxy formation (Dekel & Silk 1986), that were worked out in the frame of the cold dark matter (CDM) scenarios in- cluding biasing, dwarf galaxies should originate from the 1 fluctuations, and ought to be more evenly distributed than the high rare density peaks which form the giants. In these scenar- ios the dwarf galaxies should trace the underlying dark mat- ter and are expected to fill the voids. Since there was a hint that emission-line galaxies are more evenly distributed (Salzer