2022ApJ...928..179L

With Σ_SFR ∼ 4200 M_☉ yr^–1 kpc^–2, SPT 0346-52 (z = 5.7) is the most intensely star-forming galaxy discovered by the South Pole Telescope. In this paper, we expand on previous spatially resolved studies, using ALMA observations of dust continuum, [N II] 205 µm, [C II] 158 µm, [O I] 146 µm, and undetected [N II] 122 µm and [O I] 63 µm emission to study the multiphase interstellar medium (ISM) in SPT 0346-52. We use pixelated, visibility-based lens modeling to reconstruct the source-plane emission. We also model the source-plane emission using the photoionization code CLOUDY and find a supersolar metallicity system. We calculate T_dust = 48.3 K and λ_peak = 80 µm and see line deficits in all five lines. The ionized gas is less dense than comparable galaxies, with n_e < 32 cm^–3, while ∼20% of the [C II] 158 µm emission originates from the ionized phase of the ISM. We also calculate the masses of several phases of the ISM. We find that molecular gas dominates the mass of the ISM in SPT 0346-52, with the molecular gas mass ∼4x higher than the neutral atomic gas mass and ∼100x higher than the ionized gas mass.