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Arxiv: JWST MIRI detections of Hα and [O III] and direct metallicity measurement of the z=10.17 lensed galaxy MACS0647-JD Published: 4/24/2024 11:53:16 PM Updated: 4/24/2024 11:53:16 PM

Paper abstract: JWST spectroscopy has revolutionized our understanding of galaxies in theearly universe. Covering wavelengths up to 5.3\,{\rm \mu m}, NIRSpec candetect rest-frame optical emission lines H\alpha out to z = 7 and [O III]to z = 9.5. Observing these lines in more distant galaxies requires longerwavelength spectroscopy with MIRI. Here we present MIRI MRS IFU observations ofthe lensed galaxy merger MACS0647-JD at z = 10.165. With exposure times of4.2 hours in each of two bands, we detect H\alpha at 9\sigma, [OIII]\,\lambda5008 at 11\sigma, and [O III]\,\lambda4960 at 3\sigma.Combined with previously reported NIRSpec spectroscopy that yields sevenemission lines including the auroral line [O III]\,\lambda4363, we presentthe first direct metallicity measurement of a z > 10 galaxy: 12+{\rmlog(O/H)}= 7.79\pm0.09, or 0.13^{+0.02}_{-0.03}\,Z_{\odot}. This is similarto galaxies at z ~ 4 - 9 with direct metallicity measurements, thoughhigher than expected given the high specific star formation rate {\rm log(sSFR/ yr^{-1})} = -7.4 \pm 0.3. We further constrain the ionization parameter{\rm log}(U) = -1.9 \pm 0.1, ionizing photon production efficiency {\rmlog}(\xi_{\rm ion}) = 25.3\pm0.1, and star formation rate5.0\pm0.6\,M_{\odot}/{\rm yr} within the past 10\,{\rm Myr}. Theseobservations demonstrate the combined power of JWST NIRSpec and MIRI forstudying galaxies in the first 500 million years.