JWST/NIRSpec Balmer-line Measurements of Star Formation and Dust Attenuation at z~3-6

TL;DR

This study uses JWST/NIRSpec spectroscopy to measure Balmer decrements in galaxies at redshifts 2.7 to 6.5, enabling direct assessment of star formation rates and dust attenuation, and revealing a stable dust attenuation-mass relationship over cosmic time.

Contribution

It provides the first spectroscopic measurement of the star-forming main sequence at z>3 using Balmer lines and investigates dust attenuation evolution up to z~6.5.

Findings

Star formation main sequence traced at z>3 with direct Balmer line measurements.

Dust attenuation at fixed stellar mass shows little evolution up to z~6.5.

Stable dust attenuation-mass relationship challenges models of galaxy evolution.

Abstract

We present an analysis of the star-formation rates (SFRs) and dust attenuation properties of star-forming galaxies at $2.7\leq z<6.5$ drawn from the Cosmic Evolution Early Release Science (CEERS) Survey. Our analysis is based on {\it JWST}/NIRSpec Micro-Shutter Assembly (MSA) $R\sim1000$ spectroscopic observations covering approximately $1-5$$\mu$m. Our primary rest-frame optical spectroscopic measurements are H$\alpha$/H$\beta$ Balmer decrements, which we use as an indicator of nebular dust attenuation. In turn, we use Balmer decrements to obtain dust-corrected H$\alpha$-based SFRs (i.e., SFR(H$\alpha$)). We construct the relationship between SFR(H$\alpha$) and stellar mass ($M_*$) in three bins of redshift ($2.7\leq z< 4.0$, $4.0\leq z< 5.0$, and $5.0\leq z<6.5$), which represents the first time the star-forming main sequence has been traced at these redshifts using direct spectroscopic measurements of Balmer emission as a proxy for SFR. In tracing the relationship between SFR(H$\alpha$) and $M_*$ back to such early times ($z>3$), it is essential to use a conversion factor between H$\alpha$ and SFR that accounts for the subsolar metallicity prevalent among distant galaxies. We also use measured Balmer decrements to investigate the relationship between dust attenuation and stellar mass out to $z\sim6$. The lack of significant redshift evolution in attenuation at fixed stellar mass, previously confirmed using Balmer decrements out to $z\sim2.3$, appears to hold out to $z\sim 6.5$. Given the rapidly evolving gas, dust, and metal content of star-forming galaxies at fixed mass, this lack of significant evolution in attenuation provides an ongoing challenge to explain.