stars from @Massey90 observed on the same night using the same instrument configuration.

MOSFIRE
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MOSFIRE was used in its default configuration. For instrumental details we refer the reader to @Steidel14. We observed four masks in $Y$ band and two in $K$ band, using integration times of 180s with ABAB dithering to improve sky subtraction. Reductions were performed with the MOSFIRE Data Reduction Pipeline (DRP) made available by the instrument team[^3].

Redshift Determination
======================

Each observed source was assessed independently by two co-authors to determine the redshift and associated quality flag. These results were then compared for conflicts in either redshift or quality flag. Conflicts were reconciled through a joint review of the spectra, usually with the help of a third, independent reviewer. As a final step in the process, we investigated all Q=4 (highest quality, see §4.1) sources for which the spectroscopic redshift ($z_s$) was highly discrepant from the expected photometric redshift ($z_p$, defined as the median photometric redshift of sources in the relevant SOM cell). Specifically, we investigated all sources with $\lvert z_{p} - z_{s} \rvert / (1 + z_{s}) \geq 0.15$. For most of these outliers, the spectroscopic redshift was deemed solid and we discuss the nature 