The Size Evolution of Passive Galaxies: Observations from the Wide Field Camera 3 Early Release Science Program

We present the size evolution of passively evolving galaxies at z similar to 2 identified in Wide-Field Camera 3 imaging from the Early Release Science program. Our sample was constructed using an analog to the passive BzK galaxy selection criterion, which isolates galaxies with little or no ongoing star formation at z greater than or similar to 1.5. We identify 30 galaxies in similar to 40 arcmin(2) to H < 25 mag. By fitting the 10-band Hubble Space Telescope photometry from 0.22 mu m less than or similar to lambda(obs) less than or similar to 1.6 mu m with stellar population synthesis models, we simultaneously determine photometric redshift, stellar mass, and a bevy of other population parameters. Based on the six galaxies with published spectroscopic redshifts, we estimate a typical redshift uncertainty of similar to 0.033(1+z). We determine effective radii from Sersic profile fits to the H-band image using an empirical point-spread function. By supplementing our data with published samples, we propose a mass-dependent size evolution model for passively evolving galaxies, where the most massive galaxies (M-* similar to 10(11) M-circle dot) undergo the strongest evolution from z similar to 2 to the present. Parameterizing the size evolution as (1+z)(-alpha), we find a tentative scaling of alpha approximate to (-0.6 +/- 0.7) + (0.9 +/- 0.4) log(M-*/10(9) M-circle dot), where the relatively large uncertainties reflect the poor sampling in stellar mass due to the low numbers of high-redshift systems. We discuss the implications of this result for the redshift evolution of the M-*-R-e relation for red galaxies.