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-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 star formation rates 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 < log(M*/Msol) < 10.5) and star formation rate (-0.5 <
log(SFR) < 2.5 in Msol yr^-1). We find that the distribution of z ~ 2.1
galaxies in stellar mass-SFR-metallicity space is clearly different from that
derived for our sample of similarly bright (L_H\b{eta} > 3 . 10^40 ergs s^-1)
local galaxies, and this offset cannot be explained by simple systematic
offsets in the derived quantities. At stellar masses above ~10^9 Msol and star
formation rates above ~10 Msol yr^-1, the z ~ 2.1 galaxies have higher oxygen
abundances than their local counterparts, while the opposite is true for
lower-mass, lower-SFR systems.
