On the evolutionary status of early-type galaxies in clusters atz≈ 0.2 - I. The Fundamental Plane

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 A 2390 are based on Multi-Object-Spectroscopy with MOSCA at the 3.5-m telescope on Calar Alto Observatory and are complemented by ground-based imaging with 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 ≥ Mr ≥ −23.0) and a rather wide field-of-view of 1.53 h −1 × 1.53 h−1 70 Mpc2. 70 Since 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 groundbased 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.