*Herschel*. The largest sample of \[\] observations in nearby starburst galaxies was presented by @Diaz2013, who obtained PACS spectroscopic observations of the 241 galaxies from the Great Observatories All-sky LIRG Survey (GOALS, @Armus2009). Further systematic studies of the \[\] emission in local galaxies have confirmed strong correlation of the \[\]/FIR deficit with $\Sigma_\mathrm{SFR}$ down to 200-pc scales, in a wide range of environments from normal galaxies [@Smith2017; @Herrera2018] to starbursts [@Diaz2017] and AGN hosts [@Herrera2018].

At the highest redshifts ($z>4$), the importance of the \[\] line increases dramatically, as the raised CMB temperature renders the low-$J$ CO emission undetectable, while the \[\] line remains relatively unaffected [@daCunha2013; @Vallini2015; @Lagache2018]. Indeed, with the advent of Atacama Large Millimeter/submillimeter Array (ALMA), \[\] observations are now increasingly used to determine redshifts and dynamical masses of high-redshift galaxies, including some of the most distant systems [@Walter2009; @Brisbin2015; @Gullberg2015; @Oteo2016; @Carniani2017; @Decarli2018; @Smit2018]. Most recently, @Gullberg2018 presented deep, 30-mas resolution (200 pc physical scale) ALMA observations of the \[\] line in four (unlensed) $z$=4.4–4.8 galaxies. Although their observation suffered from a very sparse $uv$-plane coverage, they found the resolved \[\]-FIR deficit at $z\sim$4.5 to follow the trend seen in local galaxies. Similarly, high-resolution ALMA observations 