2019ApJ...870...80L

SPT0346-52 is one of the most most luminous and intensely star-forming galaxies in the universe, with L_FIR> 10¹³ L_☉ and Σ_SFR~4200 M_☉yr^–1kpc^–2. In this paper, we present ∼0′′ / . 15 ALMA observations of the [CII] 158 µm emission line in this z = 5.7 dusty star-forming galaxy. We use a pixellated lensing reconstruction code to spatially and kinematically resolve the source-plane [CII] and rest-frame 158 µm dust continuum structure at ∼700 pc (∼0.''12) resolution. We discuss the [CII] deficit with a pixellated study of the L_[C II]_/LFIR_ ratio in the source plane. We find that individual pixels within the galaxy follow the same trend found using unresolved observations of other galaxies, indicating that the deficit arises on scales <=700 pc. The lensing reconstruction reveals two spatially and kinematically separated components (∼1 kpc and ∼500 km s^–1 apart) connected by a bridge of gas. Both components are found to be globally unstable, with Toomre Q instability parameters ≪1 everywhere. We argue that SPT0346-52 is undergoing a major merger, which is likely driving the intense and compact star formation.