2005MNRAS.358..233F

We investigate a spectroscopic sample of 48 early-type galaxies in the rich cluster Abell 2390 at z= 0.23 and 48 early-type galaxies from a previously published survey of Abell 2218 at z= 0.18. The spectroscopic data of A2390 are based on multi-object spectroscopy using the multi-object spectrograph for Calar Alto at the 3.5-m telescope on Calar Alto Observatory and are complemented by ground-based imaging using the 5.1-m Hale telescope and Hubble Space Telescope (HST) observations in the F555W and F814W filters. Our investigation spans a broad range in luminosity (-20.5 ≥M_r≥-23.0) and a rather wide field of view of 1.53h^–1₇₀x 1.53h^–1₇₀Mpc².

As the A2218 and A2390 samples are very similar, we can combine them and analyse a total number of 96 early-type (E+S0) galaxies at z∼ 0.2. Using the ground-based data only, we construct the Faber-Jackson relation (FJR) for all 96 E+S0 galaxies and detect a modest luminosity evolution with respect to the local reference. The average offset from the local FJR in the Gunn r band is. Similar results are derived for each cluster separately. Less massive galaxies show a trend for a larger evolution than more massive galaxies. HST/WFPC2 surface brightness profile fits were used to derive the structural parameters for a subsample of 34 E+S0 galaxies. We explore the evolution of the Fundamental Plane (FP) in Gunn r, its projections on to the Kormendy relation and the M/L ratios as a function of velocity dispersion. The FP for the cluster galaxies is offset from the local Coma cluster FP. At a fixed effective radius and velocity dispersion our galaxies are brighter than their local counterparts. For the total sample of 34 E+S0 cluster galaxies which enter the FP we deduce only a mild evolution with a zero-point offset of 0.10±0.06, corresponding to a brightening of 0.31±0.18 mag. Elliptical and lenticular galaxies are uniformly distributed along the FP with a similar scatter of 0.1 dex. Within our sample we find little evidence for differences between the populations of elliptical and S0 galaxies. There is a slight trend that lenticulars induce on average a larger evolution of 0.44±0.18 mag than ellipticals with 0.02 ±0.21 mag. The M/L ratios of our distant cluster galaxies at z= 0.2 are offset by Δlog(M/L_r) =-0.12±0.06 dex compared with those of Coma. Our results can be reconciled with a passive evolution of the stellar populations and a high formation redshift for the bulk of the stars in early-type galaxies. However, our findings are also consistent with the hierarchical formation picture for rich clusters, if ellipticals in clusters had their last major merger at high redshift.