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

Abstract

New photometry and spectroscopy for the two rich clusters Abell 665 and Abell 2218 are presented and used to establish the Fundamental Plane (FP) 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 compared the FP for A665 and A2218 with the FP for the three clusters CL0024+16, CL1358+62 and MS2053-04 with redshifts between 0.33 and 0.58, and with the FP for the Coma cluster. The scatter around the FP is similar for all six clusters. We find that the slope of the FP for the intermediate redshift clusters is slightly different from the one found for the Coma cluster and other nearby clusters. This may either be caused by selection effects for the intermediate redshift clusters or by differences in the evolution of low luminosity galaxies and high luminosity galaxies. The mass-to-light (M/L) ratios, as measured from the FP, change with redshift. Using the data for all five intermediate redshift clusters, we find that the M/L ratios for photometry calibrated to Gunn r change with redshift as Delta log M/L_r = (-0.26+-0.06) Delta z for q0=0.5. This is consistent with the previously published analysis for CL0024+16, CL1358+62 and MS2053-04. For q0=0.5 the results are consistent with passive evolution of a stellar population which formed at a redshift larger than five. For q0=0.15 the formation redshift must be larger than 1.7. Our new data for A665 and A2218 confirm the gradual and slow evolution of the bright E and S0 galaxies. However, possible star formation in E and S0 galaxies during the last 3-4 Gyr of the history of the Universe, as well as the selection effects complicate the interpretation of the data.