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

TL;DR

This study analyzes 317 galaxies at redshift 2-3 to understand their dust, metallicity, and star formation properties using spectroscopic and photometric data, revealing dependencies on models and attenuation curves.

Contribution

It provides a comprehensive comparison of stellar and nebular properties in high-redshift galaxies, highlighting the impact of model assumptions and attenuation curves on derived parameters.

Findings

Nebular reddening is generally larger than stellar reddening with large scatter.

High-redshift galaxies have lower metallicities and higher gas fractions compared to local galaxies.

SFR estimates from Hα and SED methods show significant scatter and depend on model choices.

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.