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We present new accurate measurements of the physical properties of astatistically significant sample of 103 galaxies at z~2 using near-infraredspectroscopy taken as part of the 3D-HST survey. We derive redshifts,metallicities and star formation rates (SFRs) from the [OII], [OIII] and Hbetanebular emission lines and exploit the multi-wavelength photometry available inCANDELS to measure stellar masses. We find the mass-metallicity relation (MZR)derived from our data to have the same trend as previous determinations in therange 0<z<3, with lower mass galaxies having lower metallicities. However wefind an offset in the relation compared to the previous determination of thez~2 MZR by Erb et al. 2006b, who measure metallicities using the [NII]/Halpharatio, with metallicities lower at a given mass. Incorporating our SFRinformation we find that our galaxies are offset from the FundamentalMetallicity Relation (FMR) by ~0.3 dex. We investigate the photoionizationconditions and find that our galaxies are consistent with the elevatedionization parameter previously reported in high-redshift galaxies. Using theBPT diagram we argue that, if this is the case, metallicity indicators based on[NII] and Halpha may not be consistent with the ones obtained via oxygen linesand Hbeta. Using a recent determination of the theoretical evolution of thestar forming sequence in the BPT diagram we convert our measured [OIII]/Hbetaline ratios to [NII]/Halpha ratios. From the [NII]/Halpha ratio we infersystematically higher metallicities in better agreement with the FMR. Ourresults thus suggest the evolution of the FMR previously reported at z~2-3 maybe an artifact of the differential evolution in metallicity indicators, andcaution against using locally calibrated metallicity relations at high redshiftwhich do not account for evolution in the physical conditions of star-formingregions.

The Mass-Metallicity-SFR Relation at z >~ 2 with 3D-HST