Balmer Decrements and Nebular-Stellar Reddening in JADES Galaxies at $2.7<z<7$

TL;DR

This study uses JWST data to analyze nebular and stellar reddening in galaxies between redshifts 2.7 and 7, revealing how dust properties relate to galaxy mass, SFR, and metallicity over cosmic time.

Contribution

It provides a new prescription to convert stellar to nebular reddening and characterizes how dust reddening depends on galaxy properties at high redshift.

Findings

Balmer decrements are consistent across redshifts at fixed stellar mass.

Differential reddening scales with mass and SFR at lower redshifts but not above z~4.

Nebular reddening correlates strongly with metallicity up to z~5.

Abstract

We aim to characterize nebular and stellar reddening in star-forming galaxies as a function of global galaxy properties (stellar mass, SFR, metallicity) at $2.7 < z< 7.0$. We also provide a prescription to convert SED-based $E(B-V)_{\mathrm{star}}$ to $E(B-V)_{\mathrm{gas}}$ when direct measurements of nebular reddening are unavailable. Our results are based on JWST/NIRSpec measurements of both individual spectra, with a sample of 283 galaxies, and composite spectra, including a larger sample of 327 galaxies. We estimate nebular reddening using the Balmer decrement (H$\alpha$/H$\beta$) above $10^{8.5}$ $M_{\odot}$, where the sample is representative. Stellar reddening and SFRs are derived through Prospector SED fitting, while gas-phase metallicities are estimated from strong emission-line ratios. At fixed stellar mass, Balmer decrements remain consistent within uncertainties across our redshift range, indicating that stellar mass primarily determines the overall dust column even by $z \sim 7$. We find that differential reddening ($\Delta E(B-V) \equiv E(B-V)_{\mathrm{gas}} - E(B-V)_{\mathrm{star}}$) scales linearly with mass and SFR at $z \sim 2.7 - 4.0$, but shows no mass or SFR dependence above $z \sim 4.0$. We find evidence for smaller $\Delta E(B-V)$ above $z \sim 5.0$, suggesting that nebular emission and stellar continuum probe increasingly similar dust columns towards higher redshift. Finally, we find that nebular reddening correlates strongly with metallicity out to $z \sim 5$, whereas the correlation between stellar reddening and metallicity is weaker or absent. Together, these results suggest that both dust mass and geometry play a significant role in shaping the observed reddening of high-redshift galaxies.