VLT/X-Shooter Near-Infrared Spectroscopy and HST Imaging of
  Gravitationally-Lensed z~2 Compact Quiescent Galaxies
  Quiescent massive galaxies at z~2 are thought to be the progenitors of
present-day massive ellipticals. Observations revealed them to be
extraordinarily compact. The determination of stellar ages, star formation
rates and dust properties via spectroscopic measurements has up to now only
been feasible for the most luminous and massive specimens (~3x M*). Here we
present a spectroscopic study of two near-infrared selected galaxies which are
close to the characteristic stellar mass M* (~0.9x M* and ~1.3x M*) and whose
observed brightness has been boosted by the gravitational lensing effect. We
measure the redshifts of the two galaxies to be z=1.71\pm0.02 and
z=2.15\pm0.01. By fitting stellar population synthesis models to their
spectro-photometric SEDs we determine their ages to be 2.4^{+0.8}_{-0.6} Gyr
and 1.7\pm0.3 Gyr, respectively, which implies that the two galaxies have
higher mass-to-light ratios than most quiescent z~2 galaxies in other studies.
We find no direct evidence for active star-formation or AGN activity in either
of the two galaxies, based on the non-detection of emission lines. Based on the
derived redshifts and stellar ages we estimate the formation redshifts to be
z=4.3^{+3.4}_{-1.2} and z=4.3^{+1.0}_{-0.6}, respectively. We use the increased
spatial resolution due to the gravitational lensing to derive constraints on
the morphology. Fitting Sersic profiles to the de-lensed images of the two
galaxies confirms their compactness, with one of them being spheroid-like, and
the other providing the first confirmation of a passive lenticular galaxy at a
spectroscopically derived redshift z~2.
