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 MF = 0.2. We have now obtained spectroscopic redshifts for 34 EIS cluster candidates with z MF = 0.2 (see also Hansen et al. 2002, AA Olsen et al. 2003. AA 2) richnesses corresponding to Abell classes R ≤ 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.