A Comparison of the Most Massive Quiescent Galaxies from z ∼ 3 to the Present: Slow Evolution in Size, and spheroid-dominated*

We use Hubble Space Telescope imaging to study the structural properties of ten of the most massive ($M \geq 10^{11.25}$ Msun) quiescent galaxies (QGs) in the UKIDSS UDS at $2.5redshifts, we find that the median size evolves as $R_e \propto H(z)^{-0.85 \pm 0.12}$ (or alternatively, $R_e \propto (1+z)^{-0.90 \pm 0.12}$). This rate of evolution is slower than that for lower mass QGs. When compared to low redshift QGs, the axis ratio distribution for our high redshift massive QG sample is most consistent with those in which spheroids are dominant. These observations point to earlier size growth among massive QGs that also resulted in spheroidal systems. Finally, we measured residual-corrected surface brightness profiles for our sample. These show that the Sersic parameterization is generally representative out to several effective radii and does not miss excess low surface brightness light. The sizes inferred from the light profiles therefore confirm the compactness of these most massive high redshift QGs.