Stellar Kinematics of z~2 Galaxies and the Inside-Out Growth of
  Quiescent Galaxies
  Using stellar kinematics measurements, we investigate the growth of massive,
quiescent galaxies from z~2 to today. We present X-Shooter spectra from the UV
to NIR and dynamical mass measurements of 5 quiescent massive (>10^11 Msun)
galaxies at z~2. This triples the sample of z>1.5 galaxies with well
constrained (dsigma <100 km/s) velocity dispersion measurements. From spectral
population synthesis modeling we find that these galaxies have stellar ages
that range from 0.5-2 Gyr, with no signs of ongoing star formation. We measure
velocity dispersions (290-450 km/s) from absorption lines and find that they
are 1.6-2.1 times higher than those of galaxies in the SDSS at the same mass.
Sizes are measured using GALFIT from HST-WFC3 H160 and UDS K-band images. The
dynamical masses correspond well to the SED based stellar masses, with
dynamical masses that are ~15% higher. We find that M_*/M_dyn may decrease
slightly with time, which could reflect the increase of the dark matter
fraction within an increasing effective radius. We combine different stellar
kinematic studies from the literature, and examine the structural evolution
from z~2 to z~0: we confirm that at fixed dynamical mass, the effective radius
increases by a factor of ~2.8, and the velocity dispersion decreases by a
factor of ~1.7. The mass density within one effective radius decreases by a
factor of ~20, while within a fixed physical radius (1 kpc) it decreases only
mildly (~2). When we allow for an evolving mass limit by selecting a population
of galaxies at fixed number density, a stronger size growth with time is found
(~4), velocity dispersion decreases by a factor of ~1.4, and interestingly, the
mass density within 1 kpc is consistent with no evolution. This finding
suggests that massive quiescent galaxies at ~2 grow inside-out, consistent with
the expectations from minor mergers.
