the ALESS survey. The ALESS survey was an ALMA Cycle 0 870 $\mu$m imaging campaign targeting all 126 sources discovered in the LABOCA Extended *Chandra* Deep Field South Submillimeter Survey (LESS, @Weiss2009). With ALMA Cycle 0 observations providing a significant improvement over the LABOCA map in both resolution (beam area reduced by a factor of $\sim$200) and sensitivity (increased by a factor of $\sim$3), the ALESS survey identified 99 distinct sub-mm bright galaxies in its primary sample [@Hodge2013]. Out of these, at the time of the proposal (2015 April) only four – ALESS 49.1, 57.1, 67.1 and 122.1 – had robust redshifts that allowed for ALMA observations of both the low-$J$ CO and \[\] lines. The spectroscopic redshifts were acquired using VLT-FORS2/VIMOS and Keck-DEIMOS, and are based on multiple line detections [@Danielson2017].

In this paper, we present the ALMA Band 8 observations targeting the \[\] line and rest-frame 160-$\mu$m continuum. The corresponding Band 3 observations, targeting the CO (3-2) ($\nu_\mathrm{rest}$=345.795 GHz) emission, were recently presented by @CR18.

ALMA Band 8 observations {#subsec:obs_band8}
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The observations were carried out as part of the ALMA Cycle 3 Project \#2015.1.00019.S (PI: J. Hodge) on 2016 August 12. Only ALESS 49.1 and ALESS 57.1 