The Fundamental Metallicity Relation at z~2-3: Complications from the Keck Baryonic Structure Survey

The cycle of gas into and out of a galaxy determines how the galaxy evolves in terms of stellar mass, gas mass, and chemical enrichment. The Fundamental Metallicity Relation (FMR) links the three parameters and quantifies the relative contribution of star formation, pristine gas infall, and enriched gas outflow to the galaxy's metallicity. Prior work has suggested that galaxies up to z~3 lie on the FMR plane, implying that the baryon cycle is generic across large portions of cosmic time. Using 275 galaxies from the Keck Baryonic Structure Survey, we look for evidence of the FMR at z~2.24 using two different methods. The first is a parametric approach, where we search for the projection of the FMR that minimises intrinsic scatter relative to the standard mass-metallicity relation (MZR). The second is a non-parametric approach, which quantifies the correlation between residuals from the MZR and a third parameter, such as SFR. We use multiple strong-line calibrations to estimate oxygen abundance and calculate SFR from H⍺ luminosity using both a constant conversion factor and a Fe-dependent conversion. Although we do see a three-parameter correlation between stellar mass, gas-phase metallicity, and SFR, we do not find evidence for a significant reduction in scatter suggesting that the FMR may not extend to higher redshifts. Therefore, while these parameters are likely coupled, the nature of the coupling is significantly different in high-z galaxies as compared to local galaxies.