We have measured the Fundamental Plane ( FP ) parameters for a sample of 30 field early-type galaxies ( E/S0 ) in the redshift range 0.1 < z < 0.66 .
We find that : i ) the FP is defined and tight out to the highest redshift bin ; ii ) the intercept \gamma evolves as d \gamma / dz = 0.58 ^ { +0.09 } _ { -0.13 } ( for \Omega = 0.3 , \Omega _ { \Lambda } = 0.7 ) , or , in terms of average effective mass to light ratio , as d \log ( M / L _ { B } ) / dz = -0.72 ^ { +0.11 } _ { -0.16 } , i. e. faster than is observed for cluster E/S0 ( -0.49 \pm 0.05 ) .
In addition , we detect [ OII ] emission > 5 Å in 22 % of an enlarged sample of 42 massive E/S0 in the range 0.1 < z < 0.73 , in contrast with the quiescent population observed in clusters at similar z .
We interpret these findings as evidence that a significant fraction of massive field E/S0 experiences secondary episodes of star-formation at z < 1 .