ALMA 26 Arcmin² Survey of GOODS-S at One Millimeter (ASAGAO): Average Morphology of High-z Dusty Star-forming Galaxies in an Exponential Disk (n ≃ 1)

We present morphological properties of dusty star-forming galaxies at z = 1-3 determined with the high-resolution (FWHM ∼ 0.″19) Atacama Large Milllimeter/submillimeter Array (ALMA) 1 mm map of our ASAGAO survey covering a 26 arcmin² area in GOODS-S. In conjunction with the ALMA archival data, our sample consists of 45 ALMA sources with infrared luminosity (L _IR) range of ∼10¹¹-10¹³ L _o. To obtain an average rest-frame far-infrared (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 our sample has an average FIR-wavelength Sérsic 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 component at the center, indicative of the existence of active galactic nuclei. The average FIR profile agrees with a morphology of an exponential disk clearly distinguished from a de Vaucouleurs spheroidal profile (Sérsic index of 4). We also examine the rest-frame optical Sérsic index n _opt and effective radius R _e,opt with 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 dusty disk-like structure is embedded within a larger stellar disk. The rest-frame UV and FIR data of HST and ALMA provide us with a radial profile of the total star formation rate (SFR), where the infrared SFR dominates over the UV SFR at the center. Under the assumption of a constant SFR, a compact stellar distribution in z ∼ 1-2 compact quiescent galaxies (cQGs) is well reproduced, while a spheroidal stellar morphology of cQGs (n _opt = 4) is not, suggestive of other important mechanism(s) such as dynamical dissipation.