these luminosity selections, galaxies can be selected via their absorption cross-section in neutral gas when there is a chance alignment of the target with a background quasar along the line of sight. Such configurations imprint strong characteristic absorption lines in the quasar spectrum, caused by the high column density gas in either disks, circum-galactic material (CGM) or galaxy haloes. The strongest classes of absorbers are the damped Lyman-$\alpha$ systems (DLAs) with neutral hydrogen column densities [@Wolfe1986], and the sub-DLAs with column densities of [@Peroux2003; @Zafar2013b]. Both classes have characteristic Lorentzian damping wings associated with their Lyman-$\alpha$ profiles. Unless otherwise specified, we will refer to sub-DLAs and DLAs uniformly as *damped absorbers*.

With a detectability that is independent of the host galaxy’s brightness, damped absorbers are believed to sample the general galaxy population in a more representative manner, probing a larger dynamic range in stellar mass, gas-phase metallicity, star formation rate and morphology at any redshift. Indeed, this assertion was confirmed by comparing how absorption- and luminosity-selections sample the underlying luminosity function [@Berry2016; @Krogager2017].

This implies that a pure selection based on damped absorbers, on average, will sample lower-mass systems often below the detection-limit in emission [@Fynbo1999; @Moller2002; @Fynbo2008; @Pontzen2008; @Fynbo2010; 