James Webb Space Telescope Feed Post

JADES: Detecting [OIII]λ4363 Emitters and Testing Strong Line Calibrations in the High-z Universe with Ultra-deep JWST/NIRSpec Spectroscopy up to z \sim 9.5 Published: 6/5/2023 9:00:00 PM Updated: 6/5/2023 9:00:00 PM

Paper abstract: We present 10 novel [OIII]\lambda 4363 auroral line detections up to z~9.5 measured from ultra-deep JWST/NIRSpec MSA spectroscopy from the JWSTAdvanced Deep Extragalactic Survey (JADES). We leverage the deepestspectroscopic observations yet taken with NIRSpec to determine electrontemperatures and oxygen abundances using the direct T_e method. We directlycompare against a suite of locally calibrated strong-line diagnostics andrecent high-z calibrations. We find the calibrations fail to simultaneouslymatch our JADES sample, thus warranting a self-consistent revision of thesecalibrations for the high-z Universe. We find weak dependence between R2 andO3O2 with metallicity, thus suggesting these line-ratios are ineffective in thehigh-z Universe as metallicity diagnostics and degeneracy breakers. We findR3 and R23 still correlate with metallicity, but we find tentative flatteningof these diagnostics, thus suggesting future difficulties when applying thesestrong-line ratios as metallicity indicators in the high-z Universe. We alsopropose and test an alternative diagnostic based on a different combination ofR3 and R2 with a higher dynamic range. We find a reasonably good agreement(median offset of 0.002 dex, median absolute offset of 0.13 dex) with the JWSTsample at low metallicity. Our sample demonstrates higher ionization/excitationratios than local galaxies with rest-frame EWs(H\beta) ~ 200 -300Angstroms. However, we find the median rest-frame EWs(H\beta) of our sampleto be ~ 2\text{x} less than the galaxies used for the local calibrations.This EW discrepancy combined with the high ionization of our galaxies does notpresent a clear description of [OIII]\lambda 4363 production in the high-zUniverse, thus warranting a much deeper examination into the factors affectingproduction.