2005ApJ...635.1006S

We present the results of near-infrared spectroscopic observations for a sample of 12 star-forming galaxies at 1.0<z<1.5, drawn from the DEEP2 Galaxy Redshift Survey. Hβ, [O III], Hα, and [N II] emission line fluxes are measured for these galaxies. Application of the O3N2 and N2 strong-line abundance indicators implies average gas-phase oxygen abundances of 50%-80% solar. We find preliminary evidence of luminosity-metallicity (L-Z) and mass-metallicity (M-Z) relationships within our sample, which spans from M_B=-20.3 to -23.1 in rest-frame optical luminosity and from 4x10⁹ to 2x10¹¹ M_☉in stellar mass. At fixed oxygen abundance, these relationships are displaced from the local ones by several magnitudes toward brighter absolute B-band luminosity and more than an order of magnitude toward larger stellar mass. If individual DEEP2 galaxies in our sample follow the observed global evolution in the B-band luminosity function of blue galaxies between z∼1 and z∼0 (Willmer et al. (ref???)2005), they will fade on average by ∼1.3 mag in M_B. To fall on local L-Z and M-Z relationships, these galaxies must increase by a factor of 6-7 in M/L_Bbetween z∼1 and z∼0 and by factor of 2 in both stellar mass and metallicity. Such concurrent increases in stellar mass and metallicity are consistent with the expectations of a ``closed-box'' chemical evolution model, in which the effects of feedback and large-scale outflows are not important. While K_s<20.0 z∼2 star-forming galaxies have similar [N II]/Ha ratios and rest-frame optical luminosities to those of the DEEP2 galaxies presented here, their higher M/L_Bratios and clustering strengths indicate that they will experience different evolutionary paths to z∼0. Finally, emission-line diagnostic ratios indicate that the z>1 DEEP2 galaxies in our sample are significantly offset from the excitation sequence observed in nearby H II regions and SDSS emission-line galaxies. This offset implies that physical conditions are different in the H II regions of distant galaxies hosting intense star formation, and may affect the chemical abundances derived from strong-line ratios for such objects.