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

Abstract

We present an analysis of the star formation rates (SFRs) and dust attenuation properties of star-forming galaxies at 2.7 ≤ z < 6.5 drawn from the Cosmic Evolution Early Release Science Survey. Our analysis is based on JWST/NIRSpec Micro-Shutter Assembly R ∼ 1000 spectroscopic observations covering approximately 1–5 μm. Our primary rest-frame optical spectroscopic measurements are Hα/Hβ Balmer decrements, which we use as an indicator of nebular dust attenuation. In turn, we use Balmer decrements to obtain dust-corrected Hα-based SFRs (i.e., SFR(Hα)). We construct the relationship between SFR(Hα) and stellar mass (M *) in three bins of redshift (2.7 ≤ z < 4.0, 4.0 ≤ z < 5.0, and 5.0 ≤ 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(Hα) and M * back to such early times (z > 3), it is essential to use a conversion factor between Hα 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 ∼ 6. The lack of significant redshift evolution in attenuation at fixed stellar mass, previously confirmed using Balmer decrements out to z ∼ 2.3, appears to hold out to z ∼ 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.

Direct T e-based Metallicities of z = 2–9 Galaxies with JWST/NIRSpec: Empirical Metallicity Calibrations Applicable from Reionization to Cosmic Noon

“…The data were reduced to produce two-dimensional (2D) spectra from which one-dimensional (1D) flux-calibrated spectra were extracted, as described in Shapley et al (2023b) and Sanders et al (2023b). A wavelength-dependent slit-loss correction was then applied to the 1D spectra (see Reddy et al 2023 for details).…”

“…Stellar population properties were inferred with the spectral energy distribution (SED) fitting code Fast (Kriek et al 2009) by fitting the flexible stellar population synthesis models of Conroy et al (2009) to public multiwavelength photometry. We assumed a delayed-τ star formation history and either solar stellar metallicity and the Calzetti et al (2000) attenuation curve or subsolar metallicity and the SMC attenuation curve (Gordon et al 2003) based on the redshift and stellar mass of the source, as detailed in Shapley et al (2023b). For roughly one third of the sample for which reduced JWST NIRCam imaging was available, models were fit to combined HST and JWST/NIRCam photometry.…”

“…SFRs were calculated using dust-corrected Hα luminosity when Hα was covered; otherwise, dust-corrected Hβ luminosity was employed. We adopt the conversion factor from Balmer line luminosity to SFR based on Z * = 0.001 BPASS binary stellar population synthesis models (Eldridge et al 2017) appropriate for moderate-and low-metallicity high-redshift systems (Reddy et al 2022;Shapley et al 2023b). SFR as a function of M * is shown in Figure 4 for the CEERS, JWST literature, and ground-based auroral-line samples, color-coded by redshift.…”

The MUSE Ultra Deep Field (MUDF). V. Characterizing the Mass–Metallicity Relation for Low-mass Galaxies at z ∼ 1–2

“…Progress is already being made in this area with revised calibrations proposed by Sanders et al (2024), Hirschmann et al (2023, and additional studies (Nakajima et al 2022;Garg et al 2023;Yang et al 2023). This rapid release of results related to the metallicities of galaxies across cosmic time should provide a consensus on these issues that was not possible before JWST (e.g., Langeroodi et al 2022;Atek et al 2023;Curti et al 2023;Heintz et al 2023;Langeroodi & Hjorth 2023;Maseda et al 2023;Matthee et al 2023;Shapley et al 2023;Sun et al 2023;Trump et al 2023;Bagley et al 2024). These investigations are crucial, as our results approach the low-metallicity limit of the current strongline calibrations.…”

“…These grids were generated for a hydrogen column density of N H = 10 21.5 cm −2 without dust. A lack of dust in the models is suitable for low-mass galaxies (Shapley et al 2022(Shapley et al , 2023, but generally has a negligible effect on the relative ratios of the same ionic species. The ratios of emission lines with fixed relative intensities, as well as those constrained to specific ranges, are provided in Table 2.…”