The evolutionary history of early-type galaxies as derived from the fundamental plane

The fundamental plane (FP) scaling relations and their evolution are a powe rful tool for studying the global properties of early-type galaxies and the ir evolutionary history. The form of the FP, as derived by surveys in the l ocal Universe at wavelengths ranging from the U to the K band, cannot be ex plained by metallicity variations alone among early-type galaxies; systemat ic variations in age, dark matter content, or homology breaking are require d. A large-scale study of early-type galaxies at 0.1 < z < 0.6 demonstrates that the SB intercept of the FP, the rest frame (U-V) colour, and the abso rption line strengths all evolve passively, thereby implying a high mean fo rmation redshift for the stellar content. The slope of the FP evolves with redshift, which is broadly consistent with systematic age effects occurring along the early-type galaxy sequence. The implication that the least lumin ous early-type galaxies formed later than the luminous galaxies is discusse d in the context of the evolution of the colour-magnitude relation, the But cher-Oemler effect and hierarchical galaxy formation models.