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 \text { km } \text { s } ^ { -1 } .
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 _ { \text { sf } } \simeq 1 – 2 Gyr and z _ { \text { form } } \simeq 2.5 – 4 , and a stellar mass of M _ { \star } \simeq 3 – 4 \times 10 ^ { 11 } M _ { \sun } .
This is in agreement with a virial mass limit of M _ { \text { vir } } < 7 \times 10 ^ { 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 \sim 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 \sim 2 massive and passive galaxies may exhibit a wide range of properties , then possibly following quite different evolutionary histories from z \sim 2 to z = 0 .