Spectral EW of Br γ, Na I, and Ca I as a function of the EW of CO 2–0. The density maps show measurements on our extracted spectra after a quality cut on the required S/N. The green x-symbols are ∼100 stars in the Wallace & Hinkle (1996, 1997) and Winge et al. (2009) spectral libraries, and the blue plus-symbols are >400 Milky Way stars from Gonneau et al. (2020). Magenta solid lines, green dashed (for Wallace & Hinkle 1996, 1997; Winge et al. 2009), and orange dot-dashed lines (Gonneau et al. 2020) show the robust mean as function of EW_CO. Stars with a Br γ measurement below the dot-dashed horizontal blue line in the left panel are affected by Br γ gas emission at the centre of the NSC.