2013ApJ...772..141B

We present rest-frame optical spectra for a sample of nine low-mass star-forming galaxies in the redshift range 1.5 < z < 3 which are gravitationally lensed by foreground clusters. We used Triplespec, an echelle spectrograph at the Palomar 200 inch telescope that is very effective for this purpose as it samples the entire near-infrared spectrum simultaneously. By measuring the flux of nebular emission lines, we derive gas-phase metallicities and star formation rates, and by fitting the optical to infrared spectral energy distributions we obtain stellar masses. Taking advantage of the high magnification due to strong lensing, we are able to probe the physical properties of galaxies with stellar masses in the range 7.8 < log M/M_☉< 9.4 whose star formation rates are similar to those of typical star-forming galaxies in the local universe. We compare our results with the locally determined relation between stellar mass, gas metallicity, and star formation rate. Our data are in excellent agreement with this relation, with an average offset < Δlog (O/H) > = 0.01±0.08, suggesting a universal relationship. Remarkably, the scatter around the fundamental metallicity relation is only 0.24 dex, smaller than that observed locally at the same stellar masses, which may provide an important additional constraint for galaxy evolution models.