  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.
