open access publication

Article, 2023

JWST/NIRSpec Measurements of the Relationships between Nebular Emission-line Ratios and Stellar Mass at z ∼ 3–6

In: The Astrophysical Journal Letters, ISSN 2041-8205, 2041-8213, Volume 950, 1, Page l1, 10.3847/2041-8213/acd939

Contributors (5)

Shapley, Alice E (Corresponding author) [1] Reddy, Naveen Admala [1] Sanders, Ryan L [1] [2] Topping, Michael W (0000-0001-8426-1141) [3] Brammer, Gabriel B (0000-0003-2680-005X) [4]


  1. [1] University of California System
  2. [NORA names: United States; America, North; OECD]
  3. [2] NHFP Hubble Fellow.
  4. [3] University of Arizona
  5. [NORA names: United States; America, North; OECD]
  6. [4] University of Copenhagen
  7. [NORA names: KU University of Copenhagen; University; Denmark; Europe, EU; Nordic; OECD]


We analyze the rest-optical emission-line ratios of star-forming galaxies at 2.7 ≤ z < 6.5 drawn from the Cosmic Evolution Early Release Science (CEERS) Survey and their relationships with stellar mass (M *). Our analysis includes both line ratios based on the [N ii] λ6583 feature ([N ii] λ6583/Hα, ([O iii] λ5007/Hβ)/([N ii] λ6583/Hα) (O3N2), and [N ii] λ6583/[O ii] λ3727) and those featuring α-elements ([O iii] λ5007/Hβ, [O iii] λ5007/[O ii] λ3727 (O32), ([O iii] λλ4959, 5007 + [O ii] λ3727)/Hβ (R23), and [Ne iii] λ3869/[O ii] λ3727). Given the typical flux levels of [N ii] λ6583 and [Ne iii] λ3869, which are undetected in the majority of individual CEERS galaxies at 2.7 ≤ z < 6.5, we construct composite spectra in bins of M * and redshift. Using these composite spectra, we compare the relationships between emission-line ratios and M * at 2.7 ≤ z < 6.5 with those observed at lower redshift. While there is significant evolution toward higher excitation (e.g., higher [O iii] λ5007/Hβ, O32, O3N2) and weaker nitrogen emission (e.g., lower [N ii] λ6583/Hα and [N ii] λ6583/[O ii] λ3727) between z ∼ 0 and z ∼ 3, we find in most cases that there is no significant evolution in the relationship between line ratio and M * beyond z ∼ 3. The [Ne iii] λ3869/[O ii] λ3727 ratio is anomalous in showing evidence for significant elevation at 4.0 ≤ z < 6.5 at fixed mass, relative to z ∼ 3.3. Collectively, however, our empirical results suggest no significant evolution in the mass–metallicity relationship at 2.7 ≤ z < 6.5. Representative galaxy samples and metallicity calibrations based on existing and upcoming JWST/NIRSpec observations will be required to translate these empirical scaling relations into ones tracing chemical enrichment and gas cycling and to distinguish among descriptions of feedback in galaxy formation simulations at z > 3.


Science Survey, analysis, bins, calibration, cases, chemical enrichment, composite spectra, cosmic evolution, cycling, description, elevation, emission, emission line ratios, empirical results, empirical scaling relations, enrichment, evidence, evolution, excitation, features, feedback, flux levels, formation simulations, galaxies, galaxy formation simulations, galaxy sample, gas cycling, high excitation, levels, line ratios, low redshift, majority, mass, mass-metallicity relationship, measurements, metallicity calibrations, most cases, nitrogen emissions, observations, one, ratio, redshift, relation, relationship, results, samples, scaling relations, significant elevation, significant evolution, simulations, spectra, star-forming galaxies, stellar mass, survey, α-elements, λ3869, λ6583


  • National Aeronautics and Space Administration