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T. Treu (Caltech)
Most of the recent studies of intermediate redshift (0.1< z < 1) early-type galaxies (E/S0) have been devoted to the cluster environment. In particular, the observed evolution of the Fundamental Plane (FP) indicates that the stellar populations of cluster E/S0 have formed at high redshift (>2).
However, it is likely that the population of galaxies in clusters evolves due to accretion of isolated galaxies and small groups. Therefore, in order to gain a reliable global picture, it is mandatory to study the evolution of E/S0 in all environments, from the core of rich clusters to the field. In addition, a specific prediction of the hierarchical clustering scenario is that major mergers and major episodes of star formation occur well below z=1 for field E/S0, while these phenomena are likely to be mostly confined to higher redshift for cluster E/S0.
I present here the results of a study of the FP for ~ 30 E/S0 in the redshift range z=0.11-0.41 (Treu et al. 1999,2001a,b), based on HST-WFPC2 imaging and ESO-3.6m spectroscopy. The investigation is being extended to z~ 0.7 by means of ESO-VLT spectroscopy (Treu et al. 2001c).