The MOSDEF survey: the mass-metallicity relationship and the existence of the FMR at z ∼ 1.5

We analyse the rest-optical emission-line ratios of z similar to 1.5 galaxies drawn from the Multi-Object Spectrometer for Infra-Red Exploration Deep Evolution Field (MOSDEF) survey. Using composite spectra, we investigate the mass-metallicity relation (MZR) at z similar to 1.5 and measure its evolution to z = 0. When using gas-phase metallicities based on the N2 line ratio, we find that the MZR evolution from z similar to 1.5 to z = 0 depends on stellar mass, evolving by Delta log(O/H) similar to 0.25 dex at M-* < 10(9.75) M-circle dot down to Delta log(O/H) similar to 0.05 at M-* greater than or similar to 10(10.5) M-circle dot. In contrast, the O3N2-based MZR shows a constant offset of Delta log(O/H) similar to 0.30 across all masses, consistent with previous MOSDEF results based on independent metallicity indicators, and suggesting that O3N2 provides a more robust metallicity calibration for our z similar to 1.5 sample. We investigated the secondary dependence of the MZR on star formation rate (SFR) by measuring correlated scatter about the mean M-*-specific SFR and M-*-log(O3N2) relations. We find an anticorrelation between log(O/H) and sSFR offsets, indicating the presence of a M-*-SFR-Z relation, though with limited significance. Additionally, we find that our z similar to 1.5 stacks lie along the z = 0 metallicity sequence at fixed mu = log(M-*/M-circle dot) - 0.6 x log(SFR/M-circle dot yr(-1)) suggesting that the z similar to 1.5 stacks can be described by the z = 0 fundamental metallicity relation (FMR). However, using different calibrations can shift the calculated metallicities off of the local FMR, indicating that appropriate calibrations are essential for understanding metallicity evolution with redshift. Finally, understanding how [NII]/H alpha scales with galaxy properties is crucial to accurately describe the effects of blended [NII] and H alpha on redshift and H alpha fiux measurements in future large surveys utilizing low-resolution spectra such as with Euclid and the Roman Space Telescope.