Strong size and internal density evolution of early-type galaxies between z \sim 2 and the present has been reported by several authors .
Here we analyze samples of nearby and distant ( z \sim 1 ) galaxies with dynamically measured masses in order to confirm the previous , model-dependent results and constrain the uncertainties that may play a role .
Velocity dispersion ( \sigma ) measurements are taken from the literature for 50 morphologically selected 0.8 < z < 1.2 field and cluster early-type galaxies with typical masses M _ { dyn } = 2 \times 10 ^ { 11 } ~ { } M _ { \odot } .
Sizes ( R _ { eff } ) are determined with Advanced Camera for Surveys imaging .
We compare the distant sample with a large sample of nearby ( 0.04 < z < 0.08 ) early-type galaxies extracted from the Sloan Digital Sky Survey for which we determine sizes , masses , and densities in a consistent manner , using simulations to quantify systematic differences between the size measurements of nearby and distant galaxies .
We find a highly significant difference between the \sigma - R _ { eff } distributions of the nearby and distant samples , regardless of sample selection effects .
The implied evolution in R _ { eff } at fixed mass between z = 1 and the present is a factor of 1.97 \pm 0.15 .
This is in qualitative agreement with semianalytic models ; however , the observed evolution is much faster than the predicted evolution .
Our results reinforce and are quantitatively consistent with previous , photometric studies that found size evolution of up to a factor of 5 since z \sim 2 .
A combination of structural evolution of individual galaxies through the accretion of companions and the continuous formation of early-type galaxies through increasingly gas-poor mergers is one plausible explanation of the observations .