The evolution of cluster E and S0 galaxies measured from the Fundamental Plane

Photometry has been obtained for magnitude limited samples of galaxies in the two rich clusters Abell 665 (37 galaxies) and Abell 2218 (61 galaxies). Both clusters have a redshift of 0.18. The limiting magnitude of the samples is 19 m in the I-band. Spectroscopy has been obtained for seven galaxies in A665 and nine galaxies in A2218, all of which also have available photometry. Spectroscopy has been obtained for two additional galaxies in A2218, one of which is a background galaxy. Effective radii re and mean surface brightnesses e were derived from the photometry. The typical uncertainties are ±0.078 in log re and ±0.12 in log e. The combination log re+0.82 loge that enters the Fundamental Plane (FP) has an uncertainty of only ±0.018. The spectroscopy was used for measurements of the velocity dispersions, σ. The typical uncertainty is ±0.023 on log σ. The data are used to establish the FP, log re = α log σ + β log e + γ, for the clusters. The FP for these two clusters adds important knowledge about the properties of E and S0 galaxies in the relatively unexplored redshift interval 0.05 to 0.3. We have