The Size Evolution of Passive Galaxies: Observations from the Wide Field
  Camera 3 Early Release Science Program
  We present results on the size evolution of passively evolving galaxies at
1<z<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>1.5. We
identify 30 galaxies in ~40 square arcmin to H<25 mag. We supplement
spectroscopic redshifts from the literature with photometric redshifts
determined from the 15-band photometry from 0.22-8 micron. We determine
effective radii from Sersic 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* ~ 10^11 Msol) galaxies undergoing the most rapid evolution
from z~2 to the present. Parameterizing the size evolution as (1+z)^{-alpha},
we find a tentative scaling between alpha and stellar mass of alpha ~ -1.8+1.4
log(M*/10^9 Msol). We briefly discuss the implications of this result for our
understanding of the dynamical evolution of the red galaxies.
