A high stellar velocity dispersion for a compact massive galaxy at z=2.2
  Recent studies have found that the oldest and most luminous galaxies in the
early Universe are surprisingly compact, having stellar masses similar to
present-day elliptical galaxies but much smaller sizes. This finding has
attracted considerable attention as it suggests that massive galaxies have
grown by a factor of ~five in size over the past ten billion years. A key test
of these results is a determination of the stellar kinematics of one of the
compact galaxies: if the sizes of these objects are as extreme as has been
claimed, their stars are expected to have much higher velocities than those in
present-day galaxies of the same mass. Here we report a measurement of the
stellar velocity dispersion of a massive compact galaxy at redshift z=2.186,
corresponding to a look-back time of 10.7 billion years. The velocity
dispersion is very high at 510 (+165, -95) km/s, consistent with the mass and
compactness of the galaxy inferred from photometric data and indicating
significant recent structural and dynamical evolution of massive galaxies. The
uncertainty in the dispersion was determined from simulations which include the
effects of noise and template mismatch. However, we caution that some subtle
systematic effect may influence the analysis given the low signal-to-noise
ratio of our spectrum.
