We examine the evolution of the relation between stellar mass surface density , velocity dispersion and half-light radius - the stellar mass fundamental plane - for quiescent galaxies at z < 0.6 .
We measure the local relation from galaxies in the Sloan Digital Sky Survey and the intermediate redshift relation from \sim 500 quiescent galaxies with stellar masses 10 \lesssim \mathrm { log } ( M _ { \ast } / M _ { \odot } ) \lesssim 11.5 .
Nearly half of the quiescent galaxies in our intermediate redshift sample are compact .
After accounting for important selection and systematic effects , the velocity dispersion distribution of galaxies at intermediate redshifts is similar to galaxies in the local universe .
Galaxies at z < 0.6 appear to be smaller ( \lesssim 0.1 dex ) than galaxies in the local sample .
The orientation of the stellar mass fundamental plane is independent of redshift for massive quiescent galaxies at z < 0.6 and the zero-point evolves by \sim 0.04 dex .
Compact quiescent galaxies fall on the same relation as the extended objects .
We confirm that compact quiescent galaxies are the tail of the size and mass distribution of the normal quiescent galaxy population .