We present deep Keck spectroscopy for 17 morphologically-selected field spheroidals in the redshift range 1.05 < z < 1.60 in order to investigate the continuity in physical properties between the claimed massive compact red galaxies ( “ nuggets ” ) at z \simeq 2 and well-established data for massive spheroidal galaxies below z \simeq 1 .
By combining Keck-based stellar velocity dispersions with HST -based sizes , we find that the most massive systems ( M _ { dyn } > 10 ^ { 11 } M _ { \odot } ) grew in size over 0 < z < 1.6 as ( 1+z ) ^ { -0.75 \pm 0.10 } ( i.e. , \times 2 since z = 1.5 ) whereas intermediate mass systems ( 10 ^ { 11 } { M } _ { \odot } > { M } _ { dyn } > 10 ^ { 10 } { M } _ { \odot } ) did not grow significantly .
These trends are consistent with a picture in which more massive spheroidals formed at higher redshift via “ wetter ” mergers involving greater dissipation .
To examine growth under the favored “ dry ” merger hypothesis , we also examine size growth at a fixed velocity dispersion .
This test , uniquely possible with our dynamical data , allows us to consider the effects of “ progenitor bias. ” Above our completeness limit ( \sigma > 200 km s ^ { -1 } ) , we find size growth consistent with that inferred for the mass-selected sample , thus ruling out strong progenitor bias .
To maintain continuity in the growth of massive galaxies over the past 10 Gyr , our new results imply that size evolution over 1.3 < z < 2.3 , a period of 1.9 Gyr , must have been even more dramatic than hitherto claimed if the red sources at z > 2 are truly massive and compact .