A Comparison of the Stellar, CO and Dust-Continuum Emission from Three,
  Star-Forming HUDF Galaxies at $z\sim 2$
  We compare the extent of the dust, molecular gas and stars in three
star-forming galaxies, at $z= 1.4, 1.6$ and $2.7$, selected from the Hubble
Ultra Deep Field based on their bright CO and dust-continuum emission as well
as their large rest-frame optical sizes. The galaxies have high stellar masses,
$\mathrm{M}_*>10^{11}\mathrm{M}_\odot$, and reside on, or slightly below, the
main sequence of star-forming galaxies at their respective redshifts. We probe
the dust and molecular gas using subarcsecond Atacama Large
Millimeter/submillimeter Array observations of the 1.3 mm continuum and CO line
emission, respectively, and probe the stellar distribution using \emph{Hubble
Space Telescope} observations at 1.6 \textmu m. We find that for all three
galaxies the CO emission appears $\gtrsim 30\%$ more compact than the stellar
emission. For the $z= 1.4$ and $2.7$ galaxies, the dust emission is also more
compact, by $\gtrsim 50\%$, than the stellar emission, whereas for the $z=1.6$
galaxy, the dust and stellar emission have similar spatial extents. This
similar spatial extent is consistent with observations of local disk galaxies.
However, most high redshift observations show more compact dust emission,
likely due to the ubiquity of central starbursts at high redshift and the
limited sensitivity of many of these observations. Using the CO emission line,
we also investigate the kinematics of the cold interstellar medium in the
galaxies, and find that all three have kinematics consistent with a
rotation-dominated disk.
