The Fundamental Plane of massive quiescent galaxies out to z~2
  The Fundamental Plane (FP) of early-type galaxies, relating the effective
radius, velocity dispersion, and surface brightness, has long been recognized
as a unique tool for analyzing galaxy structure and evolution. With the
discovery of distant quiescent galaxies and the introduction of high
sensitivity near-infrared spectrographs, it is now possible to explore the FP
out to z~2. In this Letter we study the evolution of the FP out to z~2 using
kinematic measurements of massive quiescent galaxies ($M_{*}>10^{11}
M_{\odot}$). We find preliminary evidence for the existence of an FP out to
z~2. The scatter of the FP, however, increases from z~0 to z~2, even when
taking into account the larger measurement uncertainties at higher redshifts.
We find a strong evolution of the zero point from z~2 to z~0:
$\Delta\log_{10}M/L_g\propto(-0.49\pm0.03)~z$. In order to assess whether our
spectroscopic sample is representative of the early-type galaxy population at
all redshifts, we compare their rest-frame g-z colors with those from a larger
mass complete sample of quiescent galaxies. At z>1 we find that the
spectroscopic sample is bluer. We use the color offsets to estimate a
mass-to-light ratio (M/L) correction. The implied FP zero point evolution after
correction is significantly smaller: $\Delta\log_{10}M/L_g\propto(-0.39\pm
0.02)~z$. This is consistent with an apparent formation redshift of
$z_{\rm{form}}=6.62^{+3.19}_{-1.44}$ for the underlying population, ignoring
the effects of progenitor bias. A more complete spectroscopic sample is
required at z~2 to properly measure the M/L evolution from the FP evolution.
