STAR FORMATION RATES AND METALLICITIES OF K-SELECTED STAR-FORMING GALAXIES AT z ∼ 2

We present spectroscopy of 15 star-forming BzK galaxies (sBzKs) with K(AB) less than or similar to 23 in the Subaru Deep Field, for which H alpha and some other emission lines are detected in 0.9-2.3 mu m spectra with a resolution of R = 500. Using H alpha luminosities, we obtain star formation rates (SFRs), and then specific SFRs (SSFRs) dividing SFRs by stellar masses, which are derived from SED fitting to BVRi'z'K photometry. It is found that sBzKs with higher stellar masses have larger SFRs. A negative correlation is seen between stellar mass and SSFR, which is consistent with the previous results for z similar to 2 galaxies. This implies that a larger growth of stellar mass occurs in less massive galaxies. In addition, gas-phase oxygen abundances, 12+log(O/H), are derived from the ratio of [N II](lambda 6584) to H alpha using the N2 index method. We have found a correlation between stellar mass and oxygen abundance in the sense that more massive sBzKs tend to be more metal rich, which is qualitatively consistent with the relation for UV-selected z similar to 2 galaxies. However, the metallicity of the sBzKs is similar to 0.2 dex higher than that of UV-selected galaxies with similar stellar masses, which is significant considering the small uncertainties. The sBzKs in our sample have redder R - K colors than the UV-selected galaxies. This galaxy color dependence in the oxygen abundance may be caused by older or dustier galaxies having higher metallicities at z similar to 2.