Dust Attenuation, Star Formation, and Metallicity in z ~ 2-3 Galaxies from KBSS-MOSFIRE

Abstract: We present a detailed analysis of 317 $2.0 \leq z \leq 2.7$ star-forming galaxies from the Keck Baryonic Structure Survey (KBSS). Using complementary spectroscopic observations with Keck/LRIS and Keck/MOSFIRE, as well as spectral energy distribution (SED) fits to broadband photometry, we examine the joint rest-UV and rest-optical properties of the same galaxies, including stellar and nebular dust attenuation, metallicity, and star formation rate (SFR). The inferred parameters of the stellar population (reddening, age, SFR, and stellar mass) are strongly dependent on the details of the assumed stellar population model and the shape of the attenuation curve. Nebular reddening is generally larger than continuum reddening, but with large scatter. Compared to local galaxies, high-redshift galaxies have lower gas-phase metallicities (and/or higher nebular excitation) at fixed nebular reddening, and higher nebular reddening at fixed stellar mass, consistent with gas fractions that increase with redshift. We find that continuum reddening is correlated with $12+\log(\mathrm{O}/\mathrm{H}){\mathrm{O3N2}}$ at $3.0\sigma$ significance, whereas nebular reddening is correlated with only $1.1\sigma$ significance. This may reflect the dependence of both continuum reddening and O3N2 on the shape of the ionizing radiation field produced by the massive stars. Finally, we show that H$\alpha$-based and SED-based estimates of SFR exhibit significant scatter relative to one another, and agree on average only for particular combinations of spectral synthesis models and attenuation curves. We find that the SMC extinction curve predicts consistent SFRs if we assume the sub-solar ($0.14Z{\odot}$) binary star models that are favored for high-redshift galaxies.