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Arxiv: Comparing emission- and absorption-based gas-phase metallicities in GRB host galaxies at z=2-4 using JWST Published: 10/24/2023 7:07:14 PM Updated: 4/15/2024 9:13:21 PM

Paper abstract: Much of what is known of the chemical composition of the universe is based onemission line spectra from star forming galaxies. Emission-based inferencesare, nevertheless, model-dependent and they are dominated by light fromluminous star forming regions. An alternative and sensitive probe of themetallicity of galaxies is through absorption lines imprinted on the luminousafterglow spectra of long gamma ray bursts (GRBs) from neutral material withintheir host galaxy. We present results from a JWST/NIRSpec programme toinvestigate for the first time the relation between the metallicity of neutralgas probed in absorption by GRB afterglows and the metallicity of the starforming regions for the same host galaxy sample. Using an initial sample ofeight GRB host galaxies at z=2.1-4.7, we find a tight relation betweenabsorption and emission line metallicities when using the recently proposed\hat{R} metallicity diagnostic (+/-0.2dex). This agreement implies arelatively chemically-homogeneous multi-phase interstellar medium, andindicates that absorption and emission line probes can be directly compared.However, the relation is less clear when using other diagnostics, such as R23and R3. We also find possible evidence of an elevated N/O ratio in the hostgalaxy of GRB090323 at z=3.58, consistent with what has been seen in otherz>4 galaxies. Ultimate confirmation of an enhanced N/O ratio and of therelation between absorption and emission line metallicities will require a moredirect determination of the emission line metallicity via the detection oftemperature-sensitive auroral lines in our GRB host galaxy sample.