YOUNG, STAR-FORMING GALAXIES AND THEIR LOCAL COUNTERPARTS: THE EVOLVING RELATIONSHIP OF MASS-SFR-METALLICITY SINCE z ∼ 2.1

We explore the evolution of the Stellar Mass-Star Formation Rate (SFR)-Metallicity relation using a set of 256 COSMOS and GOODS galaxies in the redshift range 1.90 < z < 2.35. We present the galaxies' rest-frame optical emission-line fluxes derived from IR-grism spectroscopy with the Hubble Space Telescope. and combine these data with SFRs and stellar masses obtained from deep, multi-wavelength (rest-frame UV to IR) photometry. We then compare these measurements to those for a local sample of galaxies carefully matched in stellar mass (7.5 less than or similar to log(M-*/M-circle dot) less than or similar to 10.5) and SFR (-0.5 less than or similar to log(SFR) less than or similar to 2.5 in M-circle dot yr(-1)). We find that the distribution of z similar to 2.1 galaxies in stellar mass-SFR-metallicity space is clearly different from that derived for our sample of similarly bright (L-H beta >3 x 10(40) erg s(-1)) local galaxies, and this offset cannot be explained by simple systematic offsets in the derived quantities. At stellar masses above similar to 10(9) M-circle dot and SFRs above similar to 10 M-circle dot yr(-1), the z similar to 2.1 galaxies have higher oxygen abundances than their local counterparts, while the opposite is true for lower-mass, lower-SFR systems.