The Detection of [O III] λ4363 in a Lensed, Dwarf Galaxy at z = 2.59: Testing Metallicity Indicators and Scaling Relations at High Redshift and Low Mass

We present Keck/MOSFIRE (Multi-Object Spectrometer for InfraRed Exploration) and Keck/LRIS (Low Resolution Imaging Spectrometer) spectroscopy of A1689-217, a lensed (magnification ~7.9), star-forming (SFR ~ 16 M_☉ yr⁻¹), dwarf (log(M_★/M_☉) = 8.07–8.59) Lyα emitter (EW₀ ~ 138 Å) at z = 2.5918. Dwarf galaxies similar to A1689-217 are common at high redshift and likely responsible for reionization, yet few have been studied with detailed spectroscopy. We report a 4.2σ detection of the electron-temperature-sensitive [O iii] λ4363 emission line and use this line to directly measure an oxygen abundance of 12 + log(O/H) = 8.06 ± 0.12 (~1/4 Z_☉). A1689-217 is the lowest-mass galaxy at z > 2 with an [O iii] λ4363 detection. Using the rest-optical emission lines, we measure A1689-217's other nebular conditions, including electron temperature (T e ([O iii]) ~ 14,000 K), electron density (n e ~ 220 cm⁻³), and reddening (E(B-V) ~ 0.39). We study relations between strong-line ratios and direct metallicities with A1689-217 and other galaxies with [O iii] λ4363 detections at z ~ 0–3.1, showing that the locally calibrated, oxygen-based, strong-line relations are consistent from z ~ 0 to 3.1. We also show additional evidence that the O₃₂ versus R₂₃ excitation diagram can be utilized as a redshift-invariant, direct-metallicity-based, oxygen abundance diagnostic out to z ~ 3.1. From this excitation diagram and the strong-line ratio–metallicity plots, we observe that the ionization parameter at fixed O/H is consistent with no redshift evolution. Although A1689-217 is metal-rich for its M_★ and star formation rate, we find it to be consistent within the large scatter of the low-mass end of the fundamental metallicity relation

Vie Économique : Dimensions politiques

Revue Vie Économique Sujet : La Revue Vie Économique est une initiative des Éditions vie économique (EVE), coopérative de solidarité. Lieu de débat et de réflexion sur les enjeux économiques, la revue veut aller au-delà de la pensée économique traditionnelle, trop souvent réduite aux seules transactions marchandes, en abordant les dimensions politique et sociétale des activités économiques contemporaines. Ceci inclut, évidemment, les enjeux écologiques qui imposent de changer nos manières..