Mass and Environment Drive the Evolution of Early–type Galaxies

New information has recently become available on the fundamental plane for various samples of early-type galaxies with redshift up to 1.3, both in clusters and in the field. This information is reviewed and clues are derived on the evolution of spheroids over the last two thirds of the Universe lifetime as a function of galaxy mass and environment, in comparison with the predictions of the hierarchical models of galaxy formation. Using the Universe as a time-machine and interpreting changes in M/L ratio as age differences, we see that the age increases with galaxy mass in all environments, cluster galaxies with any mass are older than field galaxies with the same mass, and the age difference between cluster and field galaxies increases with mass. The first two results confirm those obtained with other methods, and are reproduced by the most recent incarnation of the hierarchical models, while the third result is new and appears in contrast with the predictions of these models.