Environmental Effects in Star-Forming Dwarf Galaxies

Summary

I present here some preliminary results of a study of the spectroscopic properties of a group of star-forming dwarf galaxies that have been selected in order to sample the range in physical conditions imposed by extreme density environments. This investigation is part of an ongoing project intended to evaluate the relative influences of the environment, and the initial conditions, on the evolution of galaxies with active star formation. It has been found that, on average, starforming dwarf galaxies located in nearby low density regions appear to present spectra with higher excitation, higher Hβ equivalent widths and larger total Hβ luminosities than similar objects located within high-density environments.

Introduction

The influence of the environment on the mechanisms that control star formation is one of the most important subjects concerning the study of the origin and evolution of galaxies. Spiral galaxies in clusters, a high-density environment, have been used to trace the present-day star formation rate (SFR) in order to compare with field galaxies. Some studies of spirals in clusters suggest a reduced SFR with respect to field galaxies of the same morphological type, while others tend to favour a similar or higher SFR in cluster spirals; this question still remains open (Moss & Whittle, 1993). Current environmental effects which can be operating in galaxies as a consequence of the interaction with companions and with the intergalactic medium include, among others, tidal shaking, tidal stripping, ram pressure sweeping and evaporation.