ALMA reveals evidence for spiral arms, bars, and rings in high-redshift submillimeter galaxies

We present sub-kpc-scale mapping of the 870 $mu$m ALMA continuum emission in six luminous ($L_{rm IR}~sim~5~times10^{12}$ L$_{odot}$) submillimeter galaxies (SMGs) from the ALESS survey of the Extended Chandra Deep Field South. Our high-fidelity 0.07$u0027u0027$-resolution imaging ($sim$500 pc) reveals robust evidence for exponential dust disks which exhibit sub-kpc structure. The large-scale morphologies of the structures are suggestive of bars, star-forming rings, and spiral arms. The individual structures have deconvolved sizes of $lesssim$0.5-1 kpc, and they collectively make up $sim$2-20% of the total 870 $mu$m continuum emission we recover from a given galaxy. The ratio of the `ringu0027 and `baru0027 radii (1.7$pm$0.3) agrees with that measured for such features in local galaxies. These structures are consistent with the idea of tidal disturbances, with their detailed properties implying flat inner rotation curves and Toomre-unstable disks ($Qu003c1$). The inferred one-dimensional velocity dispersions ($sigma_{rm r}lesssim$ 70-160 km s$^{-1}$) are consistent with the limits implied if the sizes of the largest structures are comparable to the Jeans length. We create maps of the star formation rate density on $sim$500 pc scales and show that the SMGs appear to be able to sustain high rates of star formation over much larger physical scales than local (ultra-)luminous infrared galaxies. However, on 500 pc scales, they do not exceed the Eddington limit set by radiation pressure on dust. If confirmed by kinematics, the potential presence of non-axisymmetric structures would provide a means for net angular momentum loss and efficient star formation, helping to explain the very high star formation rates measured in SMGs.