Kiloparsec-scale dust disks in high-redshift luminous submillimeter
  galaxies
  We present high-resolution (0.16$"$) 870um Atacama Large
Millimeter/submillimeter Array (ALMA) imaging of 16 luminous (L_IR ~ 4 x 10^12
L_sun) submillimeter galaxies (SMGs) from the ALESS survey of the Extended
Chandra Deep Field South. This dust imaging traces the dust-obscured star
formation in these z~2.5 galaxies on ~1.3 kpc scales. The emission has a median
effective radius of $R_e=0.24" \pm 0.02"$, corresponding to a typical physical
size of $R_{e}=1.8\pm$0.2 kpc. We derive a median S\'ersic index of
$n=0.9\pm0.2$, implying that the dust emission is remarkably disk-like at the
current resolution and sensitivity. We use different weighting schemes with the
visibilities to search for clumps on 0.12$"$ (~1.0 kpc) scales, but we find no
significant evidence for clumping in the majority of cases. Indeed, we
demonstrate using simulations that the observed morphologies are generally
consistent with smooth exponential disks, suggesting that caution should be
exercised when identifying candidate clumps in even moderate S/N
interferometric data. We compare our maps to comparable-resolution HST
H$_{160}$-band images, finding that the stellar morphologies appear
significantly more extended and disturbed, and suggesting that major mergers
may be responsible for driving the formation of the compact dust disks we
observe. The stark contrast between the obscured and unobscured morphologies
may also have implications for SED fitting routines that assume the dust is
co-located with the optical/near-IR continuum emission. Finally, we discuss the
potential of the current bursts of star formation to transform the observed
galaxy sizes and light profiles, showing that the $z\sim0$ descendants of these
SMGs are expected to have stellar masses, effective radii, and gas surface
densities consistent with the most compact massive (M_* ~ 1-2 x 10^11 M_sun)
early-type galaxies observed locally.
