JWST MIRI detections of H and O III and direct metallicity measurement of the z=10. 17 lensed galaxy MACS0647-JD

JWST spectroscopy has revolutionized our understanding of galaxies in the early universe. Covering wavelengths up to 5. 3\, m, NIRSpec can detect rest-frame optical emission lines H out to z = 7 and O III to z = 9. 5. Observing these lines in more distant galaxies requires longer wavelength spectroscopy with MIRI. Here we present MIRI MRS IFU observations of the lensed galaxy merger MACS0647-JD at z = 10. 165. With exposure times of 4. 2 hours in each of two bands, we detect H at 9, O III\, 5008 at 11, and O III\, 4960 at 3. Combined with previously reported NIRSpec spectroscopy that yields seven emission lines including the auroral line O III\, 4363, we present the first direct metallicity measurement of a z > 10 galaxy: 12+ log (O/H) = 7. 790. 09, or 0. 13^+0. 02-₀. ₀₃\, Z_. This is similar to galaxies at z 4 - 9 with direct metallicity measurements, though higher than expected given the high specific star formation rate log (sSFR / yr^{-1) } = -7. 4 0. 3. We further constrain the ionization parameter log (U) = -1. 9 0. 1, ionizing photon production efficiency log (₈₎₍) = 25. 30. 1, and star formation rate 5. 00. 6\, M_/ yr within the past 10\, Myr. These observations demonstrate the combined power of JWST NIRSpec and MIRI for studying galaxies in the first 500 million years.