JADES: The Star Formation and Dust Attenuation Properties of Galaxies at 3<z<7

TL;DR

This paper leverages JWST/NIRSpec spectroscopy from the JADES program to measure the Balmer decrement ($H\alpha/H\beta$) in 602 galaxies across $3<z<7$, enabling dust-corrected H$\alpha$ star formation rates that account for subsolar metallicities. By combining medium-resolution emission-line measurements with Prospector-based SED fitting, the authors map the star formation main sequence in two redshift bins and quantify dust attenuation through the Balmer decrement, nebular reddening, and their relation to stellar reddening and the UV slope. They find that the Balmer decrement–stellar mass relation is already in place to $z\sim7$ with little evolution, that dust attenuation patterns (nebular vs stellar) depend on specific star formation rate, and that UV slope is a poor dust proxy for high-sSFR galaxies, implying more complex dust geometry or composition at high redshift. These results provide robust constraints on SFR indicators and dust properties in early galaxies, informing models of galaxy evolution during the peak epoch of star formation and the reionization era.

Abstract

We present the star formation and dust attenuation properties for a sample of 602 galaxies at redshifts $\rm{3<z<7}$, as part of the JADES survey. Our analysis is based on measurements of the $\rm{H}α/\rm{H}β$ Balmer Decrement using medium resolution (R$\sim$1000) spectroscopic observations with the JWST/NIRSpec Micro-Shutter Assembly. Stellar masses and star formation rates (SFRs) are inferred with \texttt{Prospector} using deep multi-band imaging. We utilize the Balmer decrement to measure dust-corrected H$α$-based SFRs, taking into account the subsolar metallicities observed in galaxies at high redshift. We confirm, with our large sample size, that the correlation between the Balmer decrement and stellar mass is already established out to $z\sim7$. We find that the relation between the Balmer decrement and stellar mass does not significantly evolve from the local universe to $z\sim7$. We investigate the UV slope as a function of the Balmer optical depth and find that the best-fit correlation for our high redshift sample is sSFR dependent and significantly different at high redshift when compared to galaxies at $z\approx 0$ and $z \approx 2$. For the highest sSFR galaxies in our sample, there is no significant correlation between the UV slope and Balmer optical depth. This is evidence that the UV slope should be used with great caution to correct for dust in high redshift galaxies.

Figures (5)

• Figure 1: The left panel shows the dust-corrected $\mathrm{SFR}_{\rm H\alpha}$ vs. the stellar mass for our sample of galaxies. The solid lines show the best-fit relation from Simmonds2025 for the median redshifts in the two different bins, at $z=4$ and $z=6$. Galaxies with low Balmer decrement measurements, $H\alpha/H\beta<2.75$ within their $3\sigma$ uncertainties, are shown with black marker outlines. Typical uncertainties are shown in the lower right corner. The right panel shows the SFR averaged over the last 10 Myr measured from the SED fitting vs. the stellar mass. The points are color-coded by their burstiness, defined as the fraction of the SFR average over 10 Myr and the the SFR sustained over 100 Myr. 92% of galaxies with burstiness values $>5$ have low stellar masses $M_*< 10^{8.5} \rm{M}_{\odot}$.
• Figure 2: Balmer Decrement, H$\alpha/\rm{H}\beta$, vs. the spectroscopic redshift for our sample of 602 galaxies. The points are color-coded based on their H$\alpha/\rm{H}\beta$ S/N. Individual emission lines have an S/N of H$\alpha>5$ and H$\beta>3$. The horizontal dashed line indicates a value of 2.86 for the Balmer Decrement, which is the Case B limit. A total of twenty-six galaxies fall below 2.75 within their 3$\sigma$ uncertainties and are indicated with black marker outlines.
• Figure 3: The left panel shows the Balmer Decrement, H$\alpha/\rm{H}\beta$, as a function of M$_*$, while the right panel shows the nebular reddening, E(B - V)$_{\rm{neb}}$, as a function of M$_*$. Galaxies in the redshift range $3\leq z<5$ are shown in green, and those in the redshift range $5\leq z<7$ are shown in blue, with their corresponding typical uncertainties in the upper right corner. The green and blue lines represent the medians in four stellar mass bins, with the error on the median shown as errorbars. The black contours show the 16th, 50th, and 84th percentiles for local SDSS galaxies. In the left panel, the purple diamonds and lines show the running median for $z\sim2.3$ star-forming galaxies in the MOSDEF survey from Shapley2022. In the right panel, the purple line shows the linear regression fit at z=$1.4-2.6$ from Shivaei2020. The dashed line is shown to indicate that the sample from Shivaei2020 is not complete below a stellar mass of $\sim 10^{9.5}\ M_{\odot}$.
• Figure 4: UV slope vs. Balmer optical depth. The relation from Battisti2016 at z=0 is shown as a dashed line while the relations from Reddy2015 at $z\sim 2$ are shown as dotted lines. Reddy2015 divided their sample based on sSFR values and found differing relations. The top dotted line shows the relation for galaxies with $-9.60< \log(\mathrm{sSFR/yr^{-1}})< -8.84$ and the bottom line for galaxies with $-8.84< \log(\mathrm{sSFR/yr^{-1}})< -8.00$. We separate our sample in to three bins based on sSFR. The yellow line shows the relation found for galaxies with $-11.8< \log(\mathrm{sSFR/yr^{-1}})< -9$, the orange line shows the relation for galaxies with $-9.00< \log(\mathrm{sSFR/yr^{-1}})< -8.00$, and the purple line shows the relation for galaxies with $-8.00< \log(\mathrm{sSFR/yr^{-1}})< -6.9$.
• Figure 5: The nebular reddening, $\mathrm{E(B-V)_{nebular}}$ as measured by the Balmer decrement, vs. the stellar reddening, $\mathrm{E(B-V)_{stellar}}$ as measured by the UV slope. In the left panels, points are color-coded based on their sSFR. The solid line indicates the one-to-one relation and the dashed line corresponds to the local relation from Calzetti2000. Areas where $\mathrm{E(B-V)<0}$ are shaded in gray. The right panels show the reddening ratio, $\mathrm{E(B-V)_{nebular}/E(B-V)_{stellar}}$, as a function of the sSFR. Typical uncertainties are shown in the bottom left corners. The medians are shown as diamonds for three differing sSFR bins. The bootstrapped uncertainties on the median are smaller than the marker size.