Program: GS-2007B-Q-204

The UKIDDS Ultra Deep Survey (UDS) is by far the largest, deep near-infrared (JHK) survey in existence, and the first capable of sampling truly representative cosmological volumes (100x100 Mpc at z=3). We are currently using the unique UDS data-set to study the size evolution of the most massive galaxies (M>10^11 solar) in the redshift interval 0.0<z<2.5, based on a complete, statistical sample of ~4000 galaxies. This work has demonstrated that by z=1.5 massive galaxies are significantly more compact than their local counterparts, and that the two populations cannot be linked without recourse to some form of dynamical evolution. However, the robustness of this result is currently limited by the inherent systematic uncertainties in stellar mass estimates at z>1 based on photometric redshifts alone. This proposal aims to rectify this limitation by obtaining spectroscopic redshifts for ~150 massive (M>10^11 solar) galaxies in the redshift interval 0.8<z<1.5.