Extrapolating the Evolution of Galaxy Sizes to the Epoch of Reionization

We use data on the high-redshift evolution of the size distribution and luminosity function of galaxies to constrain the relationship between their star formation efficiency and starburst lifetime. Based on the derived scaling relations, we predict the angular sizes and average surface brightnesses of faint galaxies that will be discovered with JWST. We find that JWST will be able to resolve galaxies at the magnitude limit m<31 out to a redshift of z~14. The next generation of large ground-based telescopes will resolve all galaxies discovered with JWST, provided they are sufficiently clumpy to enable detection above the bright thermal sky. We combine our constraints with simple models for self regulation of star formation, and show that feedback from supernovae at redshifts z>3 is likely mediated through momentum transfer, with the starburst timescale set by the lifetime of the massive stars rather than the dynamical time in the host galactic disk.