We examine the relation between surface brightness, velocity dispersion, and size—the fundamental plane (FP)—for quiescent galaxies at intermediate redshifts in the COSMOS field. The COSMOS sample consists of ~150 massive quiescent galaxies with an average velocity dispersion of s ~ 250 km s-1 and redshifts between 0.2 and redshifts between 0.2 and redshifts between 0.2 n4000 index; bluer galaxies and those with smaller Dn4000 indices have larger offsets. Stellar population synthesis models indicate that the massive COSMOS galaxies are younger and therefore brighter than similarly massive quiescent galaxies in the local universe. Passive evolution alone brings the massive compact quiescent (MCQ) COSMOS galaxies onto the local FP at z = 0. Therefore, evolution in size or velocity dispersion for MCQ galaxies since z ~ 1 is constrained by the small scatter observed in the FP. We conclude that MCQ galaxies at z ? 1 are not a special class of objects but rather the tail of the mass and size distribution of the normal quiescent galaxy population.
