James Webb Space Telescope Feed Post

Harvard ADS: JWST MIRI detections of H\alpha and [O III] and direct metallicity measurement of the z=10.17 lensed galaxy MACS0647-JD

Paper abstract: JWST spectroscopy has revolutionized our understanding of galaxies in the early universe. Covering wavelengths up to 5.3\,{\rm \mu m}, NIRSpec can detect 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 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\alpha at 9\sigma, [O III]\,\lambda5008 at 11\sigma, and [O III]\,\lambda4960 at 3\sigma. Combined with previously reported NIRSpec spectroscopy that yields seven emission lines including the auroral line [O III]\,\lambda4363, we present the first direct metallicity measurement of a z > 10 galaxy: 12+{\rm log(O/H)}= 7.79\pm0.09, or 0.13^{+0.02}_{-0.03}\,Z_{\odot}. This is similar to galaxies at z ~ 4 - 9 with direct metallicity measurements, though higher 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 {\rm log}(\xi_{\rm ion}) = 25.3\pm0.1, and star formation rate 5.0\pm0.6\,M_{\odot}/{\rm yr} within the past 10\,{\rm Myr}. These observations demonstrate the combined power of JWST NIRSpec and MIRI for studying galaxies in the first 500 million years.