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Using the MOSFIRE near-infrared multi-slit spectrograph on the Keck 1Telescope, we have secured high signal-to-noise ratio absorption line spectrafor six massive galaxies with redshift 2 < z < 2.5. Five of these galaxies lieon the red sequence and show signatures of passive stellar populations in theirrest-frame optical spectra. By fitting broadened spectral templates we havedetermined stellar velocity dispersions and, with broad-band HST and Spitzerphotometry and imaging, stellar masses and effective radii. Using this enlargedsample of galaxies we confirm earlier suggestions that quiescent galaxies at z> 2 have small sizes and large velocity dispersions compared to local galaxiesof similar stellar mass. The dynamical masses are in very good agreement withstellar masses (log Mstar/Mdyn = -0.02 +/- 0.03), although the averagestellar-to-dynamical mass ratio is larger than that found at lower redshift(-0.23 +/- 0.05). By assuming evolution at fixed velocity dispersion, not onlydo we confirm a surprisingly rapid rate of size growth but we also consider thenecessary evolutionary track on the mass-size plane and find a slope alpha =dlogR / dlogM > ~2 inconsistent with most numerical simulations of minormergers. Both results suggest an additional mechanism may be required toexplain the size growth of early galaxies.

MOSFIRE Absorption Line Spectroscopy of z > 2 Quiescent Galaxies: Probing a Period of Rapid Size Growth