Multi-Phase ISM in the z = 5.7 Hyperluminous Starburst SPT0346-52
  SPT0346-52 (z=5.7) is the most intensely star-forming galaxy discovered by
the South Pole Telescope, with Sigma_SFR ~ 4200 Msol yr^-1 kpc^-2. In this
paper, we expand on previous spatially-resolved studies, using ALMA
observations of dust continuum, [NII]205 micron, [CII]158 micron, [OI]146
micron, and undetected [NII]122 micron and [OI]63 micron emission to study the
multi-phase interstellar medium (ISM) in SPT0346-52. 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
lambda_peak = 80 micron, 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 [CII]158 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 SPT0346-52, with the molecular gas mass ~4x
higher than the neutral atomic gas mass and ~100x higher than the ionized gas
mass.
