HFF cluster observations of z~4-8 galaxies

These uncertainties range from ~10pc for the smallest sources to 100pc for the largest. Using a forward-modeling procedure to model the impact of incompleteness and magnification uncertainties, we characterize the size-luminosity relation at both z~4 and z~6-8. We find that the source sizes of star-forming galaxies at z~4 and z~6-8 scale with luminosity L as L^0.54+/-0.08^ and L_0.40+/-0.04^, respectively, such that lower-luminosity (>~-18mag) galaxies are smaller than expected from extrapolating the size-luminosity relation at high luminosities (<~-18mag).

The new evidence for a steeper size-luminosity relation (3{sigma}) adds to earlier evidence for small sizes based on the prevalence of highly magnified galaxies in high-shear regions, theoretical arguments against upturns in the LFs, and other independent determinations of the size-luminosity relation from the HFF clusters.