The Majority of Compact Massive Galaxies at z~2 are Disk Dominated
  We investigate the stellar structure of massive, quiescent galaxies at z~2,
based on Hubble Space Telescope/WFC3 imaging from the Early Release Science
program. Our sample of 14 galaxies has stellar masses of M* > 10^{10.8} Msol
and photometric redshifts of 1.5 < z < 2.5. In agreement with previous work,
their half-light radii are <2 kpc, much smaller than equally massive galaxies
in the present-day universe. A significant subset of the sample appears highly
flattened in projection, which implies, considering viewing angle statistics,
that a significant fraction of the galaxies in our sample have pronounced
disks. This is corroborated by two-dimensional surface brightness profile fits.
We estimate that 65% +/- 15% of the population of massive, quiescent z~2
galaxies are disk-dominated. The median disk scale length is 1.5 kpc,
substantially smaller than the disks of equally massive galaxies in the
present-day universe. Our results provide strong observational evidence that
the much-discussed ultra-dense high-redshift galaxies should generally be
thought of as disk-like stellar systems with the majority of stars formed from
gas that had time to settle into a disk.
