A z=1.82 Analog of Local Ultra-massive Elliptical Galaxies
  We present observations of a very massive galaxy at z=1.82 which show that
its morphology, size, velocity dispersion and stellar population properties
that are fully consistent with those expected for passively evolving
progenitors of today's giant ellipticals. These findings are based on a deep
optical rest-frame spectrum obtained with the Multi-Object InfraRed Camera and
Spectrograph (MOIRCS) on the Subaru telescope of a high-z passive galaxy
candidate (pBzK) from the COSMOS field, for which we accurately measure its
redshift of z=1.8230 and obtain an upper limit on its velocity dispersion
sigma_star<326 km/s. By detailed stellar population modeling of both the galaxy
broad-band SED and the rest-frame optical spectrum we derive a
star-formation-weighted age and formation redshift of t_sf~1-2 Gyr and
z_form~2.5-4, and a stellar mass of M_star~(3-4)x10^{11} M_sun. This is in
agreement with a virial mass limit of M_vir<7x10^{11}M_sun, derived from the
measured sigma_star value and stellar half-light radius, as well as with the
dynamical mass limit based on the Jeans equations. In contrast with previously
reported super-dense passive galaxies at z~2, the present galaxy at z=1.82
appears to have both size and velocity dispersion similar to early-type
galaxies in the local Universe with similar stellar mass. This suggests that
z~2 massive and passive galaxies may exhibit a wide range of properties, then
possibly following quite different evolutionary histories from z~2 to z=0.
