Multi-object spectroscopy of low redshift EIS clusters. III. Properties of optically selected clusters

We have carried out an investigation of the properties of low redshift EIS clusters using both spectroscopy and imaging data. We present new redshifts for 738 galaxies in 21 ESO Imaging Survey (EIS) Cluster fields. We use the "gap"-technique to search for significant overdensities in redshift space and to identify groups/clusters of galaxies corresponding to the original EIS matched filter cluster candidates. In this way we spectroscopically confirm 20 of the 21 cluster candidates with a matched-filter estimated redshift z sub(MF) = 0.2. We have now obtained spectroscopic redshifts for 34 EIS cluster candidates with z sub(MF) = 0.2. Of those we spectroscopically confirm 32 with redshifts ranging from z = 0.064 to 0.283. We find that: 1) the velocity dispersions of the systems range from sigma sub(v) less than or equal to 130 km s super(-1) to sigma sub(v) = 1200 km s super(-1), typical of galaxy groups to rich clusters; 2) richnesses corresponding to Abell classes R less than or equal to 1; and 3) concentration indices ranging from C = 0.2 to C = 1.2. From the analysis of the colours of the galaxy populations we find that 60% of the spectroscopically confirmed systems have a "significant" red sequence. These systems are on average richer and have higher velocity dispersions. We find that the colour of the red sequence galaxies matches passive stellar evolution predictions.