The SINS/zC-SINF Survey of z~2 Galaxy Kinematics: The Nature of
  Dispersion Dominated Galaxies
  We analyze the spectra, spatial distributions and kinematics of Ha, [NII] and
[SII] emission in a sample of 42, z~2.2 UV/optically selected star forming
galaxies (SFGs) from the SINS & zC-SINF surveys, 35 of which were observed in
the adaptive optics mode of SINFONI. This is supplemented by kinematic data
from 48 z~1-2.5 galaxies from the literature. We find that the kinematic
classification of the high-z SFGs as `dispersion dominated' or `rotation
dominated' correlates most strongly with their intrinsic sizes. Smaller
galaxies are more likely `dispersion-dominated' for two main reasons: 1) The
rotation velocity scales linearly with galaxy size but intrinsic velocity
dispersion does not depend on size, and as such, their ratio is systematically
lower for smaller galaxies, and 2) Beam smearing strongly decreases large-scale
velocity gradients and increases observed dispersion much more for galaxies
with sizes at or below the resolution. Dispersion dominated SFGs may thus have
intrinsic properties similar to `rotation dominated' SFGs, but are primarily
more compact, lower mass, less metal enriched and may have higher gas
fractions, plausibly because they represent an earlier evolutionary state.
