ALMA 26 Arcmin$^{2}$ Survey of GOODS-S at One-millimeter (ASAGAO):
  Average Morphology of High-$z$ Dusty Star-Forming Galaxies is an
  Exponential-Disk ($n \simeq 1$)
  We present morphological properties of dusty star-forming galaxies at z=1-3
determined with high-resolution (FWHM~0"19) Atacama Large
Milllimeter/submilimeter Array (ALMA) 1-mm band maps of our ASAGAO survey
covering a 26-arcmin^2 area in GOODS-S. In conjunction with the ALMA archival
data, the present sample consists of 42 ALMA sources with a wide rest-frame
far-infrared (FIR) luminosity L_FIR range of ~10^11-10^13 Lo. To obtain an
average rest-frame FIR profile, we perform individual measurements and careful
stacking of the ALMA sources using the uv-visibility method that includes
positional-uncertainty and smoothing-effect evaluations through Monte-Carlo
simulations. We find that the dusty star-forming galaxies have the average
FIR-wavelength Sersic index and effective radius of n_FIR=1.2+/-0.2 and
R_e,FIR=1.0-1.3 kpc, respectively, additionally with a point source at the
center, indicative of the existence of AGN. The average FIR profile agrees with
a morphology of an exponential-disk clearly distinguished from a spheroidal
profile (Sersic index of 4). We also examine the rest-frame optical Sersic
index n_opt and effective radius R_e,opt with the deep Hubble Space Telescope
(HST) images. Interestingly, we obtain n_opt=0.9+/-0.3 (~n_FIR) and
R_e,opt=3.2+/-0.6 kpc (>R_e,FIR), suggesting that the FIR-emitting disk is
embedded within a larger stellar disk. The rest-frame UV and FIR data of HST
and ALMA provide us a radial surface density profile of the total
star-formation rate (SFR), where the FIR SFR dominates over the UV SFR at the
center. Under the simple assumption of a constant SFR, a compact stellar
distribution found in z~1-2 compact quiescent galaxies (cQGs) is well
reproduced, while a spheroidal stellar morphology of cQGs (n_opt=4) cannot,
suggestive of other important mechanisms such as dynamical dissipation.
