We present results on the size evolution of passively evolving galaxies at 1 \lesssim z \lesssim 2 drawn from the Wide Field Camera 3 Early Release Science program .
Our sample was constructed using an analog to the passive BzK selection criterion , which isolates galaxies with little or no on-going star formation at z \gtrsim 1.5 .
We identify 30 galaxies in \sim 40 arcmin ^ { 2 } to H < 25 mag .
We supplement spectroscopic redshifts from the literature with photometric redshifts determined from the 15-band photometry from 0.22 - 8 ~ { } \mu m. We determine effective radii from Sérsic profile fits to the H -band image using an empirical PSF .
We find that size evolution is a strong function of stellar mass , with the most massive ( M _ { * } \sim 10 ^ { 11 } ~ { } M _ { \odot } ) galaxies undergoing the most rapid evolution from z \sim 2 to the present .
Parameterizing the size evolution as ( 1 + z ) ^ { - \alpha } , we find a tentative scaling between \alpha and stellar mass of \alpha \approx -1.8 + 1.4 \log ( M / 10 ^ { 9 } ~ { } M _ { \odot } ) .
We briefly discuss the implications of this result for our understanding of the dynamical evolution of the red galaxies .