  We present early results from a Hubble Space Telescope (HST) WFC3/IR imaging
survey of star-forming galaxies in the redshift range 1.5 < z < 3.0. When
complete, this survey will consist of 42 orbits of F160W imaging distributed
amongst 10 survey fields on the line of sight to bright background QSOs,
covering 65 arcmin^2 to a depth of 27.9 AB with a PSF FWHM of 0.18". In this
contribution, we use a subset of these fields to explore the evolution of the
galactic stellar mass-radius relation for a magnitude-limited sample of 102
spectroscopically-confirmed star forming galaxies (<SFR> ~ 30 Msun/yr) with
stellar mass M* ~ 10^{10} Msun. Although the light profile of these galaxies
often has an irregular, multi-component morphology, it is typically possible to
describe the brightest component with a Sersic profile of index n ~ 1. The
circularized half-light radius r_e of the brightest component is on average
<r_e> = 1.66 \pm 0.79 kpc (i.e., ~ 50-70% the size of local late-type galaxies
with similar stellar mass), consistent with recent theoretical models that
incorporate strong feedback from star forming regions. The mean half-light
radius increases with stellar mass and, at fixed stellar mass, evolves with
cosmic time as ~ (1+z)^{-1.42}, suggesting that high redshift star forming
galaxies may evolve onto the local stellar mass-radius relation by redshift z ~
1.
