THE SIZE-STAR FORMATION RELATION OF MASSIVE GALAXIES AT 1.5 < z < 2.5

We study the relation between size and star formation activity in a complete sample of 225 massive (M* > 5 x 10(10) M-circle dot) galaxies at 1.5 < z < 2.5, selected from the FIREWORKS UV-IR catalog of the CDFS. Based on stellar population synthesis model fits to the observed rest-frame UV-NIR spectral energy distributions, and independent MIPS 24 mu m observations, 65% of the galaxies are actively forming stars, while 35% are quiescent. Using sizes derived from two-dimensional surface brightness profile fits to high-resolution (FWHMPSF similar to 0.45) ground-based ISAAC data, we confirm and improve the significance of the relation between star formation activity and compactness found in previous studies, using a large, complete mass-limited sample. At z similar to 2, massive quiescent galaxies are significantly smaller than massive star-forming galaxies, and a median factor of 0.34 similar to +/- 0.02 smaller than galaxies of similar mass in the local universe. Thirteen percent of the quiescent galaxies are unresolved in the ISAAC data, corresponding to sizes <1 kpc, more than five times smaller than galaxies of similar mass locally. The quiescent galaxies span a Kormendy relation which, compared to the relation for local early types, is shifted to smaller sizes and brighter surface brightnesses and is incompatible with passive evolution. The progenitors of the quiescent galaxies were likely dominated by highly concentrated, intense nuclear starbursts at z similar to 3-4, in contrast to star-forming galaxies at z similar to 2 which are extended and dominated by distributed star formation.